Health and Safety Laboratory Harpur Hill Buxton SK17 9JN Tel: 01298 218000

Health and Safety Laboratory
Harpur Hill
Buxton SK17 9JN
Tel: 01298 218000
Fax: 01298 218590
EXAMINATION OF PRESSURE DRUMS
HSL/2005/56
Project Leader: J Joel BSc
Author(s): J Joel BSc
Science Group: Engineering Control group
© Crown copyright 2005
ACKNOWLEDGEMENTS
I wish to thank Ineosfluor and Rhodia for supplying the two drums that were used in this work.
ii
CONTENTS
1
2
3
4
5
6
7
8
Introduction ........................................................................................................................... 1
Drum 1 .................................................................................................................................. 2
2.1
Visual examination........................................................................................................ 2
2.2
Markings on drum ......................................................................................................... 2
2.3
Internal examination...................................................................................................... 3
2.4
Thickness measurements............................................................................................... 3
2.5
External examination..................................................................................................... 6
2.6
Magnetic particle inspection ......................................................................................... 7
2.7
Metallography ............................................................................................................... 7
2.8
Vickers hardness tests ................................................................................................... 8
2.9
Tensile tests ................................................................................................................... 9
2.10 Charpy tests ................................................................................................................... 9
2.11 Chemical analysis.......................................................................................................... 9
2.12 Radiography and ultrasonics of drum ends ................................................................. 10
Drum 2 ................................................................................................................................ 11
3.1
Visual examination...................................................................................................... 11
3.2
Markings on the drum ................................................................................................. 11
3.3
Internal examination.................................................................................................... 12
3.4
Thickness measurements............................................................................................. 13
3.5
External examination................................................................................................... 15
3.6
Magnetic particle inspection ....................................................................................... 15
3.7
Metallography ............................................................................................................. 16
3.8
Vickers hardness tests ................................................................................................. 17
3.9
Tensile tests ................................................................................................................. 17
3.10 Charpy tests ................................................................................................................. 17
3.11 Chemical analysis........................................................................................................ 17
3.12 Radiography and ultrasonics of drum ends ................................................................. 18
3.13 Boundary element map................................................................................................ 19
Assessment.......................................................................................................................... 20
Criteria and recommendations ............................................................................................ 24
Conclusions ......................................................................................................................... 26
References ........................................................................................................................... 27
Appendices.......................................................................................................................... 53
8.1
Appendix1 - Tensile tests drum 1................................................................................ 54
8.2
Appendix 2 – Charpy tests drum 1.............................................................................. 57
8.3
Appendix 3 – Chemical analysis drum 1..................................................................... 61
8.4
Appendix 4 – NDT reports drum 1 ............................................................................. 62
8.5
Appendix 5 - Tensile tests drum 2............................................................................... 66
8.6
Appendix 6 – Charpy drum 2 ...................................................................................... 69
8.7
Appendix 7 – Chemical analysis drum 2..................................................................... 71
8.8
Appendix 8 – NDT reports drum 2 ............................................................................. 74
8.9
Appendix 9 – Boundary element map of join between shell and end plate ................ 77
iii
EXECUTIVE SUMMARY
Objectives
There is an ageing population of pressure drums in the UK. Many drums had been made in the
1960s and early 1970s. The drums had been made to static pressure vessel codes, and it was not
clear how cyclic duty, road loading and low temperature had been dealt with. Design life criteria
had not been considered and end life was determined by periodic inspection by a competent
person using criteria for gas cylinders.
The objective of this work was to try to determine the criteria for the onset of ageing
degradation so that this can be applied to the drum population allowing any suspect drums to be
removed from service before any problems occur.
Main findings
Drum 1 had been manufactured from steel not specified on the drum specification document
GC107. The steel that should have been used had a silicon addition that leads to an
improvement in the low temperature properties of the steel.
The Charpy values obtained on testing samples from both drums were below the values
required, in current standards, at –200C, in the weld metal on Drum 1and in the parent plate on
Drum 2. The Charpy result at 00C in the weld on drum 1 was also below the required level.
The analysis of the steels showed high phosphorus and sulphur levels. The lower phosphorus
and sulphur levels in modern steels gives improved ductility whereas the higher levels of
phosphorus and sulphur lower fatigue life, therefore the fatigue life of these old drums must be
considered suspect.
The circumferential weld at each end of the drums was used as a ‘rolling band’. Poor weld
profiles could affect the stresses that the circumferential weld undergoes when moved using
these bands. One half of the weld circumference on drum 2 showed a large weld bead that
showed an incompletely filled groove at the weld toe.
Internal examination of the drums was difficult due to the restricted viewing holes at one end
where the valve would be fitted. Only approximately ⅔ to ¾ of the length of the longitudinal
weld could be observed and no assessment could be made of gap between the shell and the end
plate through which the interior was being viewed. Therefore no effective internal examination
was possible, without the aid of mirrors and an endoscope.
This design of drum, with the circumferentially welded dished ends, where the sides of the shell
and end plates touch each other for approximately 15 to 25mm adjacent to the root of the weld,
make it impossible to examine the gap between the two plates for corrosion or other problems.
The calculated minimum wall thickness of drum 1 was 6.6mm; thickness measurements carried
out on drum 1 revealed that it had a thickness of less than 6.6mm at 17 out of 40 readings. This
indicates that the drum should be withdrawn from service.
Radiography and ultrasonic testing of the circumferential weld on each drum revealed numerous
weld defects around the circumferential weld at each end of each drum. Typical defects noted
were lack of fusion, gas pores, blowholes and poor weld bead and root profiles. Comparison
iv
with BSENISO 5817 indicates that the drums should be withdrawn from service due to the
presence of the lack of fusion indicated by the radiography.
The inclusion content in the plates that made up each drum was far higher and in a generally
more deleterious form than the inclusion content in modern steels.
Recommendations
The criteria for the examination of ageing pressure drums to determine if they are suitable to
remain in service are given below. Whether all of the criteria are applied to each individual
drum or to a significant number within an identified batch of drums needs to be discussed.
The criteria that have been determined through this work fall into two categories, destructive
and non-destructive. Comparison of the results of the non-destructive examinations (in
particular) with the relevant standards and guidance documents will give an easy ‘remain in
service or destroy’ indication.
Obviously, a drum would be unusable after being subjected to the destructive criterion. To
satisfactorily calculate the continued life of a pressure drum the standards and guidance require
the impact properties of the material. The only way of determining this retrospectively is to take
samples from the plates and test them, thus destroying the integrity of that drum, but providing
useful data for assessing other drums.
Non-destructive criteria can indicate whether a particular drum needs to be removed from
service:1. A thickness survey of the drum shell, using a significant number of thickness readings should
be compared with the calculated minimum thickness allowed from the specification to which
the drum was manufactured.
2. Radiography and ultrasonic testing can be used to determine the integrity of the welds, in
particular the circumferential welds. Care should be taken to make sure that defects in any
deleterious direction are picked up by the method.
3. Any dents in the drum shell need to be assessed against the relevant standards.
4. The weld profile and other visible features of the welds should be examined and compared to
the requirements in the relevant standards.
5. Internal inspection needs to carried out but the major limitation with these designs of drums is
the difficulty of examining the welds near to the observation point and it is impossible to tell if
there is any corrosion or problems with the root of the weld where the end plate and shell plates
run parallel to each other at each end of the drum.
v
1
INTRODUCTION
Two drums were supplied to HSL for examination to determine criteria for the onset of ageing
degradation.
There is an ageing population of pressure drums in the UK. Many of the drums currently in use
had been manufactured in the 1960’s and early 1970’s. The drums had been manufactured using
static pressure vessel codes and it was not clear how cyclic duty, road loading and low
temperature properties had been dealt with. Design life criteria for the drums had not been
considered and end of life was determined by a periodic inspection by a competent person using
criteria used for gas cylinders. Other concerns were poor weld profiles, the standard of NDT
available at the time of manufacture and, compared with steels produced these days, the steel
used to manufacture the drums was very dirty, ie it contained many inclusions, many in
deleterious forms.
The drums that were supplied for examination at HSL both had a body formed into a tube from
plate and welded longitudinally and both had concave dished ends welded circumferentially into
the drum body. The circumferential weld bead also appeared to act as a rolling band to keep the
body of the cylinder clear of the surface/floor etc.
Drum 1 had been manufactured for low-pressure use and drum 2 had been manufactured for use
at higher pressure. Both drums had been used to convey refrigerant gases.
The photographs have been taken by staff from the Visual Presentation Services Section of HSL
working under my instructions. The black and white photographs and the digital photographs
were taken by myself.
The accuracy of the measured dimensions in this report is ±0.01mm for readings to two decimal
places and all other measurements are for indication only.
1
2
2.1
DRUM 1
VISUAL EXAMINATION
Figure 1 shows drum 1 as received. The drum was approximately 2085mm long and
approximately 750 mm in diameter. The drum had been constructed from plate material made
into a tube of diameter approximately 750mm and the sides of the plate joined with a
longitudinal weld. Two concave domed ends welded into position around the circumference
closed the ends of the tube. The circumferential weld bead around each end was raised and
formed the rolling bands for the drum. One end of the drum had a rectangular plate 105mm by
208mm welded to it centrally with two 42.7mm holes in it that were the positions for the valves,
shown in Figure 2, this end of the drum will be referred to as the ‘open’ end. The other end of
the drum with no openings, shown in Figure 3, will be referred to as the ‘closed’ end in this
report. In each corner of the plate there was one 15.6mm diameter threaded stud that protruded
from the surface of the plate for between 66 and 67mm, there were also two shorter studs
arranged longitudinally in the middle of the plate between the two holes, they were 15.6mm in
diameter and protruded 41mm and 42.5 mm from the plate.
2.2
MARKINGS ON DRUM
There was a large brass plate on the closed end of the drum and a small brass plate on the open
end of the drum; there were also several markings that had been stencilled onto each of the
domed ends and two adhesive labels. The markings were as follows:
Large round plate on the closed end of the drum.
ICI
SPEC:-
GC 107 230
No. R 3747
Tested:- 24.9.64
2 G 93T
9 69
6 7?
9 84
TP 345 PSIG
WCY 1682lbs
Tare 760lbs
Green adhesive label on closed end
Non-flammable compressed gas
‘ARCTON’ 22
CHLORODIFLUORMETHANE
To charge with liquid, cylinder must be positioned vertically upright. ‘DIP PIPE FITTED’
2
Stencilled onto closed end
A22
810 KGS
Small plate on open end
SPEC GC 107 230
No 3747
Stencilled onto open end
810 KGS
TARE 348
A22
3747
Green diamond-shaped adhesive label on the open end
A black silhouette of a cylinder with NON-FLAMMABLE COMPRESSED GAS (in black)
across the centre of the diamond underneath the cylinder and with ‘2’ in the bottom corner
2.3
INTERNAL EXAMINATION
The internal surface of the drum was visually examined through the two 42.7mm holes in the
dished open end of the drum. A torch was used as illumination; this was shone through one of
the two holes while looking at the internal surface of the drum through the other hole. Viewing
the interior in this way provided only a minimal view of the inside and was further complicated
by the presence of the four large and two smaller threaded studs around the two holes that
prevented the observers face from being put close to the hole. The inside of the drum appeared
to have a light coating of corrosion product but nothing severe. No problems could be observed
with the gap between the shell of the drum and the closed end plate, however it must be noted
that this gap was approximately 2m from the viewing position and relied upon the illumination
from the torch. No indication of any problems could be detected visually in the 25mm length
where the two plates touched each other adjacent to the weld root.
The internal surface of approximately two thirds to three quarters of the length of the
longitudinal weld could be observed through the holes, and this appeared to be satisfactory.
However NO assessment could be made of the remaining length of the longitudinal weld or the
gap between the shell of the drum and the end plate through which the interior was being
viewed, as there was no suitable way of looking backwards to see these areas.
After the ends of the drum had been cut off internal examination of the ends could be made. The
corrosion product was a light coating and did not appear to be any worse in the tight gap
between the drum shell and the end plate.
2.4
THICKNESS MEASUREMENTS
A grid was marked onto the drum body that gave the positions at which thickness measurements
were made. Six bands were marked on the cylindrical body of the drum and these were divided
into seven bands circumferentially, giving forty-two positions at which thickness readings were
taken. The circumferential bands were arranged evenly either side of the longitudinal weld. The
3
thickness measurements were taken using an uncalibrated Krautkramer DM2 digital wall
thickness meter.
Table 1 Wall thickness measurements Drum1 in mm
Position
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Measurement
6.6
6.4
6.8
6.5
6.1
6.6
6.9
6.7
6.4
6.8
7.0
6.4
6.4
6.7
6.6
6.6
7.0
7.0
6.7
6.9
6.6
Position
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
Measurement
6.5
6.9
6.8
7.0
6.6
6.4
6.5
6.9
6.9
6.8
7.0
6.4
6.7
7.0
6.6
6.9
6.7
6.8
6.8
The open end of the drum was marked with three positions at which thickness measurements
were made and the closed end was marked with five positions using the Krautkramer DM2
digital thickness meter. The results of the measurements are shown in tables 2 and 3.
Table 2 Wall thickness measurements of the open end in mm
Position
43
44
45
Measurement
7.7
7.7
7.7
Table 3 Wall thickness measurements of the closed end in mm
Position
46
47
48
49
50
Measurement
7.4
7.5
7.6
7.6
7
Specification documents for the drum had been received from Ineos Fluor, they had the
specification number GC107 and were dated 1959. These documents stated that “The vessels
shall be designed in accordance with BS1500: 1949 with the exceptions noted below”.
4
Design formulae:- Cylindrical shell section.
The thickness shall not be less than the greater value of each of the following formulae:
t=pDi
2fJ-P
or
t=0.027√Di
Where t =min. shell thickness in inches
p =design working pressure in lb/in2
Di =internal diameter of shell in inches
f = max. allowable design stress lb/in2
J =weld factor =0.9 for class 1 longitudinal butt weld
Max. allowable design stress =
Shell – ¼ of specification minimum UTS of parent metal
Ends – ¾ of that allowed for cylindrical shell section
Specified minimum UTS of shell material = 26tsi =58240psi
f = ¼ x 58240 = 14560psi
test pressure = 345 psig on plate on drum
test pressure = 1.5x design working pressure
design working pressure = test pressure
1.5
= 345
1.5
=230psi
The internal diameter of the drum was measured, Di =29.5 inches
Based on this I calculated the minimum wall thickness of the drum from the two formulae.
t = 0.027 √Di
=0.027 x √29.5
=0.027 x 5.43139
t =0.1466 inches = 3.724mm
t = pDi
2fJ-p
= 230 x29.5
(2x14560 x0.9) –230
= 6785
25978
t= 0.26 inches = 6.6mm
Using the two formulae to calculate the wall thickness of the shell and comparing the results
with the measurements of the wall thickness recorded earlier in the section it can be seen that
the remaining shell wall thickness is as low as 6.1mm at one position with 10 readings out of 40
at less than 6.6mm, and 17 readings out of 40 at 6.6mm or less. Therefore using this calculated
criteria the drum should be withdrawn from service following the statement in bold type at the
top of the page from GC107, as its wall thickness is now less than 6.6mm in a number of areas
on the shell.
5
On the test sheets, for the material from which the drum had been manufactured, supplied with
the specification document GC107 and dated 1959, the plate thickness was to be in the range
0.280/ 0.320ins. (7.11/8.13mm).
2.5
EXTERNAL EXAMINATION
The bolt studs around the valve holes in the open end plate were in good condition there was no
corrosion product present and the threads were clean and undamaged.
Examination of the external surface of the longitudinal weld revealed no detrimental features on
the weld itself. However in one position there was a crack in the paint at the weld toe, shown in
Figure 4. This may indicate a problem at the toe of the weld or may simply be the paint cracking
with age.
The grid used for the wall thickness measurements has been used to locate the position of the
defects. Examination of the outside of the drum indicated a number of dents in the surface of the
body and in particular there were numerous dents around both ends of the drum adjacent to the
weld bead that appears to act as the rolling band at each end. Many of the dents were small and
barely visible, there were, however, several larger dents that had a measurable depression. The
dents were measured by laying a ruler across the indentation and measuring the depth between
the drum body and the ruler with a calibrated calliper.
BS EN 14208:2004 “Transportable gas cylinders. – Specification for welded pressure drums up
to 1000 litre capacity for the transport of gases. – Design and construction”, which, although it
is intended for newly constructed drums gives criteria against which dents in a drum can be
assessed to determine if they are acceptable or not. The relevant information is contained in
Table A1 – ‘manufacturing defects in welded steel drums and rejection criteria’, of Appendix A
– ‘Description, evaluation of manufacturing defects and conditions for rejection of welded steel
pressure drums at time of visual inspection’ of the above standard.
The entry in this standard for dents is as follows:Dent
Description – A depression in the drum that has neither penetrated or removed metal and is
greater in depth than 1% of the outside diameter of the drum.
Conditions and/or actions – When the depth of the dent exceeds 3% of the external diameter of
the drum, and/or, when the diameter of the dent is less than 15 times its depth; then the action
required for both of these criteria is ‘Repair if possible followed by heat treatment of the drum,
or, scrap’.
The drum is 750mm in diameter externally, therefore any depression that is deeper the 7.5mm
(1% of the outside diameter) can be assessed against the above criteria. The dents measured on
this drum are reported on in the following part of this section and have been assessed against
this part of the standard.
The indentation at position 32, shown in Figure 5 was oval and approximately 210mm in the
longitudinal direction by 130mm circumferentially and was approximately 11.1mm deep.
Figure 6 shows the dent at position 32 as seen on the inside of the drum. This dent was 1.47% of
the drum diameter. Action needs to be taken when the dent exceeds 3% of the external diameter
and when the diameter of the dent is less than 15 times its depth. 15 times the depth of this dent
is 166.5mm; therefore it does not meet the repair or scrap criteria in the circumferential
direction, as the measurement was 130mm.
6
The indentation at position 12 and shown in Figure 7 consisted of two rings; one side of one of
the rings gave a deeper indentation. The total area affected was 55mm in the longitudinal
direction and 80mm circumferentially and the maximum depth of the indentation was 6.8mm,
shown in Figure 8. Figure 9 shows the appearance of the dent on the inside of the drum. At
0.9% of the external diameter it is not classified as a dent but 15 times the depth of the dent
gives 102mm and this makes the dimensions of the indentation less than 15 times its depth,
which indicates that consideration should be given to the repair of this indentation or scrapping
of the drum.
The indentation at position 13 and shown in Figure 10 was oval and measured approximately
140mm in the longitudinal direction and 110mm circumferentially, the maximum depth of the
indentation was 7.5mm. This indentation was 1% of the drum diameter. 15 times the depth of
the dent is 112.5mm; therefore, it doesn’t meet the criteria in the circumferential direction.
There was another indentation at position 11 shown in Figure 11, the maximum depth was
3.84mm and the total area affected was 110mm in the longitudinal direction and 50mm
circumferentially. 15 times the depth of the indentation is 57.6mm; therefore it doesn’t meet the
criteria in the circumferential direction. The dents at positions 11, 12 and 13 were all in a line
and could be seen readily on the internal surface.
2.6
MAGNETIC PARTICLE INSPECTION
After removing the paint either side of the longitudinal weld Magnetic Particle Inspection was
carried out along the weld, no cracks were observed. Magnetic Particle Inspection of the internal
weld also showed that no surface –breaking cracks were present.
Magnetic particle inspection was carried out over the indentations visible on the inside of the
drum; indentations 11, 12, 13 and 32 were inspected. No internal cracks were detected at the
indentation positions
2.7
METALLOGRAPHY
From the visual examination of the circumferential welds it was difficult to determine how the
end pieces of the drum were fitted into the shell, therefore, microsections were taken at a
random position around the circumference and across the circumferential welds at each end of
the drum to show the construction of the ends and the microstructure of the plates from which
the drum shell and the end pieces had been manufactured. A third microsection was prepared
that bisected the longitudinal weld.
Figure 12 shows the section through the circumferential weld at the open end of the drum. The
microsection shows that the end plate was bent over at the end and a weld had been made
between the end of the shell and the bent over end plate. Figures 13 and 14 show the inclusion
content of the steels used to manufacture the shell and the end plate respectively. The inclusions
present in the shell were numerous elongated manganese sulphide inclusions and a few
elongated silicate inclusions throughout the section. The end plate contained many more
elongated stringers than the shell.
Figure 15 shows the section through the circumferential weld at the closed end of the drum. The
construction of the joint was the same as that at the other end. Figure 16 shows the many
elongated manganese sulphide inclusions and stringers of broken silicate inclusions present in
the closed end plate.
7
Figure 17 shows the section across the longitudinal weld. There were no indications of any
defects present at the weld toes.
Figures 18, 19 and 20 show the microstructures in the shell, open end plate and closed end plate
of the drum respectively. The grain size in the shell steel is smaller than that in the two end
plates. The microstructures are all ferrite and pearlite with some spherodised pearlite present,
typical of a low carbon steel.
Microsections were taken in both the longitudinal (with respect to the axis of the drum) and
transverse directions to determine the rolling direction of the shell plate. Figure 21 shows
elongated inclusions in the longitudinal microsection and Figure 22 also shows elongated
inclusions but in the transverse microsection, the microstructure in both sections was banded
ferrite and pearlite. As there are elongated inclusions in both the transverse and longitudinal
direction it would appear that the plates had been cross-rolled, ie. the plates had been turned
through 900 between passes in the rolling mill that would give elongated inclusions in both
directions.
Examination of the crevice between the shell and the end plates showed some shallow pitting,
approximately 0.05mm deep, close to the weld joining the two plates together.
Following the NDT, carried out by the NDT contractor employed, certain areas were identified
as being of interest, see Section 2.12 of this report; microsections were taken from several of
these areas.
A random section was taken from the circumferential weld at the closed end of the cylinder to
break open and to observe the root of the weld. One side of the section was polished to find the
end of the gap between the shell and end plate. A small extension was observed at the end of the
gap that appeared to be linked to a pore in the weld metal, as shown in Figure 23. After
preparation part of the extension had disappeared but the rest remained as shown in Figure 24.
The extension was from the weld root and into the weld bead at 450 to the gap between the
plates. The distance between the pore and the plates was 1mm.
A second section was cut and after sectioning through most of the weld the section was broken
open using the gap between the two plates. Figure 25 shows the result. There were twenty-five
small features along the 11mm cross-section of the weld root shown in the Figure. Each of the
features looks like a small corrosion pit that has extended from the gap between the plates into
the weld metal.
A section was taken through the planar defect detected by the NDT contractor and the resultant
section is shown in Figure 26. The extension extends for 0.2mm into the weld metal.
2.8
VICKERS HARDNESS TESTS
Vickers hardness tests were carried out on the microsections in accordance with BS EN ISO
6507 – 1: 1998 ‘Metallic materials – Vickers hardness test. Part 1 – Test method’, using a 10kg
load. The results, with an accuracy of ±3% are as follows:Position
Open end of drum
Shell
End plate
Weld
Range
Average
Equivalent tensile strength
138 to 146
159
165 to189
142
159
180
492MPa (31.9tsi)
552MPa (35.9tsi)
8
Longitudinal weld
149 to 170
Closed end of drum
Shell
129
End plate
183 to 189
Weld
169 to181
162
129
185
177
445MPa (28.9tsi)
633MPa (41tsi)
The hardness values were consistent with the observed microstructures and the equivalent
tensile strengths were derived from conversion tables.
2.9
TENSILE TESTS
Sections for tensile tests were taken from the shell of the drum, in accordance with Section
14.4.1 – Transverse tensile test and Figure 6 of BS EN 14208:2004. The results obtained are
shown in Appendix 1.
Tensile tests carried out on the original plates and reported in the test certificates provide with
the specification for the drum were as follows:Original Tensile test results on parent metal
Yield stress
18.85 to 20.4 tsi
UTS
27.3 to 29.2 tsi
% elongation 24 to 29%
Recent tests
18.85 to 19.2tsi
28.8 to 29.2 tsi
26 to 36%
Therefore on comparing the two sets of results there does not appear to have been any alteration
in the tensile properties of the steel during use.
2.10
CHARPY TESTS
There were no requirements for Charpy tests on the specification document GC107, dated 1959.
However there was a requirement to carry out Izod tests, but only at ambient temperature as
quoted from GC107:“Notched bar impact tests shall be made using the Izod form of test to BS131. Three test
specimens shall be cut lengthwise and three cut crosswise to the direction of rolling and shall be
to the dimensions shown in Figure 5a (of GC107). Alternatively, if the plate thickness is
insufficient for the provision of 10x10mm specimens the dimensions may be 10x5mm in
accordance with Figure 5b (of GC107). All specimens shall have the notch cut at the surface of
the rolled plate. The tests shall all show a minimum Izod value when tested at a temperature in
the range 150C to 250C of 25ft.lbs. for 10x10mm or 8ft.lbs for 10x5mm test pieces”
Sections for Charpy tests were taken from the shell and across the longitudinal weld, in
accordance with Sections 14.4.3.2; 14.4.3.3; 14.4.3.4, 14.4.3.5, Table 3 and Figure 7 in BS EN
14208:2004. The tests were carried out at 200C, 00C and -200C. The results are shown in
Appendix 2.
2.11
CHEMICAL ANALYSIS
A piece from each of the shell plate and two end plates were sent to Sheffield Testing
Laboratories for chemical analysis. The results are shown in Appendix 3.
9
The steel specifications were taken from BS1501 – 1506:1958 “Steels for use in the chemical,
petroleum and allied industries”. The material that the shell had been manufactured from was
consistent with steel to BS 1501- 151 B. The steel specification given in GC 107 for the shell
and the end plates was BS 1501 –161 grades B or C. Table 4 gives the analyses obtained for the
shell, and two end plates on the drum and shows how these compare with the specified
compositions for the steels from BS 1501.
Table 4 Comparison of chemical analysis of the drum plates with BS1501-151,
BS1501-161 steels
Element
Carbon
Silicon
Manganese
Phosphorus
Sulphur
Chromium
Molybdenum
Nickel
Copper
Shell
0.14
<0.002
0.76
0.035
0.039
0.07
<0.02
0.15
0.19
Open end
0.13
<0.02
0.77
0.021
0.035
0.06
<0.02
0.11
0.18
Closed end
0.15
<0.02
0.72
0.031
0.040
0.03
<0.02
0.13
0.17
BS1501-151
0.25 max
0.050
0.050
0.25max
0.15max
0.40max
0.40max
BS1501-161
0.25max
0.10-0.35
0.50min
0.050max
0.050max
0.25max
0.15max
0.40max
0.40max
Document GC107 dated July 1959, for drum 1, states that the material for the plate for the shell
and ends should be BS1501-161 Grade B or C, or, BS14 flanging and welding quality. The test
sheets for the plates used for the drum quote BS1501-151 Grade B.
The specifications for BS1501-151 and BS1501-161 are almost identical except that BS1501161 steels are silicon killed and have a minimum manganese content, otherwise all the elements
are to a maximum only. For BS1501-161 the silicon levels should be between 0.10% min. and
0.35% max, and the manganese has a minimum value of 0.50%. From this it can be seen that
analyses of the plates from Drum 1 do not meet the requirements of the specification for
BS1510-161 steel as the silicon levels are below the 0.10% minimum specified. They do,
however, meet the requirements for BS1501-151 steel. This indicates that the drum had been
manufactured from the wrong grade of steel.
2.12
RADIOGRAPHY AND ULTRASONICS OF DRUM ENDS
The two drum ends were sent to an outside NDT contactor for radiographic and ultrasonic
examination of the circumferential welds to determine if the extension features observed on the
microsections of the circumferential welds occurred only at those random positions or were part
of a defect that extended for some distance around the circumference, possibly with a much
larger extension.
The radiographic examination revealed a large number of small welding anomalies such as lack
of fusion, gas pores, slag inclusions and inclusions present in the circumferential end welds. The
results of this examination are given in Appendix 4. Most of the defects would probably be
inconsequential as a single feature over the circumference but the lack of fusion in particular
occurred in 4 out of 8 radiographs around the circumference of the open-end weld and 5 out of 8
radiographs around the circumference of the closed end weld.
The results of this radiography and ultrasonic testing were used to compare the welds and any
defects to current inspection standards, and will be discussed in more detail in the assessment.
10
3
3.1
DRUM 2
VISUAL EXAMINATION
Figure 27 shows the drum as received. The drum was approximately 2072mm long and
approximately 780 mm in diameter. The drum had been constructed from plate material made
into a tube of diameter approximately 780mm and the sides of the plate joined with a
longitudinal weld. Two domed ends welded into position around the circumference closed the
ends of the tube. Figure 28 shows the raised weld bead at one end of the drum on the left of the
photograph, part of the longitudinal weld is shown across the centre of the photograph. One end
of the drum had a circular plate 240mm in diameter welded to it centrally with two valves in
position. Each valve was held in place with three studs, shown in Figure 29. This end of the
drum will be referred to as the ‘open’ end; the other end of the drum with no openings will be
referred to as the ‘closed’ end in this report, and is shown in Figure 30.
3.2
MARKINGS ON THE DRUM
Rectangular brass plate on closed end:
SERIAL No 80
DES. CODE B.S.1500 (1978) IMDG
D.TEMP 65OC max
-20OC min
MANUF. NEI JOHN THOMPSON
MAX. Wt. RID/ADR APPROVED
R22.
785Kg
R403B.
665Kg
R134A.
790Kg
R404.
Kg
R403A.
680Kg
R502
800Kg
TW 592KG (this stamped on marking was in a different type face)
Circular brass plate on closed end:
ISC
SPEC. GC 107/380
No E.L.D. 80
TESTED 20-170
9.84
12 C 98T
MF20 4 6
F1 F2 T.P. 570 PSIG
WCY
TARE
1779
1312
LBS
LBS
Rectangular sticky label on closed end:
Left hand side of the label:
EMPTY
-hand written
……………………………erty of Rhodia Organique Fine limited. It should not be
11
refilled with………………………..We reserved the right to charge a deposit/rental
and to invoice……………value if not returned in good condition
(Grey paint present where ……… placed in the three lines of text above).
??5:
S41:
S59:
AVOID CONTACT WITH SKIN AND EYES
?? ??SE OF FIRE AND/OR EXPLOSION
DO NOT ?REATHE FUMES
REFER TO MANUFACTURER/SUPPLIER
FOR INFORMATION ON
RECOVERY RECYCLING
1205721/0799HIB
(Grey paint present where “?” placed)
Rhodia
Rhodia Organique Fine Limited
PO Box 46 St Andrews Road
Avonmouth Bristol BS11 9YF UK
Tel: (0117) 948-4242
Fax: (0117) 948-4252
On the right hand side of the label there was a green diamond with a black ‘gas cylinder’
symbol in the upper part of the diamond and underneath it in black letters:NON-FLAMMABLE
COMPRESSED GAS
And “2” in the bottom corner of the diamond
In the top left quadrant there was:LIQUEFIED GAS N.O.S. MIXTURE OF 1,1,1,2,2PENTAFLUOROETHANE
1,1,1,2-TETRAFLUOROETHANE
DIFLUOROMETHANE
In the top right hand quadrant there was:-
UN3163
In the bottom right quadrant there was:EMERGENCY No.
(0117) 938 1289
Small brass plate on open end:
SPEC. GC.
107/380
ISC
No ELD 80
3.3
INTERNAL EXAMINATION
After the valves had been removed the internal surface of the drum was examined by viewing
through one of the holes and illuminating the inside with a torch through the other hole. The
inside surface had a very light corrosion product present generally over the whole surface. There
was a longitudinal ‘run’ of heavier corrosion product that would be consistent with a fluid run in
12
the drum. No problems could be observed with the gap between the shell of the drum and the
end plate, however this was approximately 2m from the viewing position and relied upon the
illumination from the torch. No indication of any problems could be detected visually in the
15mm length where the two plates touched each other adjacent to the weld root. Only
approximately two thirds to three quarters of the longitudinal weld could be observed through
the holes and this appeared to be satisfactory. No assessment could be made of the remaining
length of the weld or the gap between the shell and the end plate through which the interior was
being viewed, as there was no suitable way of looking backwards to see these areas.
After the ends of the drum had been cut off internal examination of the ends could be made. The
corrosion product was a light coating and did not appear to be any worse in the tight gap
between the drum shell and the end plate.
3.4
THICKNESS MEASUREMENTS
A grid was marked onto the drum shell that gave the positions at which thickness measurements
were made. Six bands were marked on the cylindrical body of the drum and these were divided
into seven bands circumferentially, giving forty-two positions at which thickness readings were
taken. The circumferential bands were arranged evenly either side of the longitudinal weld. The
thickness measurements were taken using an uncalibrated Krautkramer DM2 digital wall
thickness meter and the results are contained in Table 5.
Table 5 Wall thickness measurements Drum 2 in mm
Position
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Measurement
11.6
11.5
11.5
11.5
11.5
11.7
11.3
11.3
11.5
11.7
11.3
11.8
11.7
11.5
11.9
11.7
11.7
11.8
Position
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
Measurement
11.8
11.4
11.7
11.6
11.6
11.9
11.2
11.6
11.6
11.6
11.7
11.6
11.5
11.5
11.9
11.5
11.5
11.5
The open end of the drum was marked with three positions at which thickness measurements
were made and the closed end was marked with five positions where measurements were made.
The results of the measurements are shown in Tables 6 and 7.
13
Table 6 Wall thickness measurements of the open end in mm
Position
43
44
45
Measurement
13.0
13.0
13.1
Table 7 Wall thickness measurements of the closed end in mm
Position
46
47
48
49
50
Measurement
12.9
12.9
12.8
12.9
12.9
The formulae for the shell thickness used for drum 1 have been used to calculate the wall
thickness for drum 2 but using the values for internal diameter and test pressure from drum 2.
The results of the calculations are shown below.
Design formulae:- Cylindrical shell section.
The thickness shall not be less than the greater value of each of the following formulae:
t=pDi
2fJ-p
or
t=0.027√Di
Where t =min. shell thickness in inches
p =design working pressure in lb/in2
Di =internal diameter of shell in inches
f = max. allowable design stress lb/in2
J =weld factor =0.9 for class 1 longitudinal butt weld
Max. allowable design stress =
Shell – ¼ of specification minimum UTS of parent metal
Ends – ¾ of that allowed for cylindrical shell section
Specified minimum UTS of shell material = 26tsi =58240psi
f = ¼ x 58240 = 14560psi
test pressure = 570 psig on plate on drum
test pressure = 1.5x design working pressure
design working pressure = test pressure
1.5
= 570
1.5
=380psi
Di =29.75 inches
14
t = pDi
2fJ-p
= 380 x29.75
(2x14560 x0.9) –380
= 11305
25828
t = 0.4377 inches = 11.1mm
t = 0.027 √Di
=0.027 x √29.75
=0.027 x 5.45
t =0.147 inches = 3.733mm
Comparing these results with the measurements of the wall thickness recorded earlier in the
section it can be seen that all of the results are larger than the greater value obtained from the
two formulae, ie they were greater than 11.1mm. The measured wall thicknesses were, however,
only just above the 11.1mm calculated value and therefore, in my opinion, would need to be
checked at subsequent fills to ensure that the wall thickness did not fall below 11.1mm.
3.5
EXTERNAL EXAMINATION
External examination revealed numerous small dents and some score marks, shown in Figures
31 and 32. Some of the score marks were relatively deep and measurements have been made of
these where possible.
As the valves were removed from the drum four of the six studs holding them in position were
removed with the nuts leaving two studs in position. Figure 33 shows the two studs in position
in the end plate. The studs were 16.3mm in diameter and the ones that remained in the drum
extended for 41mm from the surface of the drum. All of the studs had a heavy corrosion product
on them, the central unthreaded part of the stud had a heavy corrosion product on it and the
corrosion product completely filled the threads where the spring washer had been positioned.
The corrosion product can be seen on the studs in Figure 33. Figure 34 shows a stud with the
nut still attached, note the clean threads where the stud came out of the end plate. Where the
studs remained attached to the nut there was no indication that the nut had loosened from the
stud at all.
One length of the circumferential weld at the open end of the drum was larger than the
remainder of the weld bead. The weld in this length had a different profile on the side of the
bead nearest the edge of the drum. There appeared to be some undercut at the weld toe in this
area. Diametrically opposite, the weld bead profile was much smoother and similar to that
observed on Drum 1 and to that on the weld bead at the closed end of this drum. Figure 35
shows the weld bead with the larger profile and Figure 36 shows the weld bead around the
remainder of this circumferential weld.
3.6
MAGNETIC PARTICLE INSPECTION
Magnetic Particle Inspection (MPI) of the external surface of the longitudinal weld was carried
out after the drum had been shot blasted. On visual examination there appeared to be some
possible problems at the weld toe, however, no indications were present on carrying out MPI.
15
Magnetic Particle Inspection of the internal weld showed that there were no cracks or other
defects present.
3.7
METALLOGRAPHY
One length of the circumferential weld at the open end of the drum was larger than in other
areas, had a different profile on the side of the bead nearest the edge of the drum and also
appeared to show some undercut at the weld toe in this area. A microsection was taken that
bisected the weld in this area, and a second microsection was taken that bisected the
circumferential weld bead diametrically opposite this area and where the weld bead had a
smoother profile. A third microsection was taken to bisect the circumferential weld bead at the
closed end of the drum. A microsection was also taken that bisected the longitudinal weld.
Figure 37 shows the section through the circumferential weld with the poor weld profile at the
open end of the drum. The microsection shows an incomplete fill of the weld bead or a large
undercut at the toe of the weld onto the end plate. There was a narrow gap between the shell and
the end plate where the end plate lies over the top of the shell plate. At the end of the gap
between the shell and end plates where the weld had been placed there was a small extension
into the weld metal, shown in Figure 38.
Figure 39 shows the microsection taken diametrically opposite the above microsection. The
profile of the weld bead on this section was much smoother, similar to the weld profile observed
on Drum 1. There was no indication of the incomplete fill/undercut shown in the other section.
This microsection also showed a small extension into the weld metal from the gap between the
shell and end plates, this is shown arrowed in Figure 40. The extension measured 0.1mm.
Figure 41 shows the microsection through the circumferential weld at the closed end of the
drum. The weld bead on this section showed a smooth profile but was slightly larger than that at
the open end of the drum. There was also a small extension into the weld metal from the gap
between the shell and the end plates. This is shown in Figure 42 and was 0.2mm in length.
Figure 43 shows the section across the longitudinal weld. The section shows that the two edges
of the plate were aligned when the weld was made. There were no indications of any defects at
the toes of the weld.
Figures 44, 45 and 46 show the microstructures in the shell, open end plate and closed end plate
respectively. The microstructure in all the plates was ferrite and pearlite, typical of low carbon
steel.
Microsections were taken in both the longitudinal (with respect to the axis of the drum) and
transverse directions to determine the rolling direction of the shell plate. Figure 47 shows
elongated inclusions in the longitudinal microsection and Figure 48 also shows elongated
inclusions but in the transverse microsection, both sections had a microstructure of banded
ferrite and pearlite. As with Drum 1 it would appear that the plate had been cross-rolled.
Examination of the crevice between the shell and the end plates revealed that the gap appeared
to be filled with scale probably from the original post weld heat treatment. It did not appear to
show any corrosion pits.
A section from the closed end circumferential weld was broken open along the gap between the
shell and end plates. The features observed are shown in Figure 49.
16
A section had been marked on the open-end circumferential weld after ultrasonic examination
that showed the position of a crack indication part way along the gap between the two plates.
This section was removed from the weld and prepared. The microsection revealed two large pits
on the surface of the plate in the area where the indication was observed. The pits were
approximately 0.18mm deep and the widest was 0.4mm. The oxide filled pits are shown in
Figure 50.
3.8
VICKERS HARDNESS TESTS
Vickers hardness tests were carried out on the microsections in accordance with BS EN ISO
6507 – 1: 1998 ‘Metallic materials – Vickers hardness test. Part 1 – Test method’, using a 10kg
load. The results, with an accuracy of ±3% are as follows:Position
Open end of drum
Shell
End plate
Weld
Range
Average
Equivalent tensile strength
121-124
126 -130
169 - 187
123
127
128
432MPa (28tsi)
442MPa (28.6tsi)
Longitudinal weld
126 - 131
Closed end of drum
Shell
End plate
Weld
116-117
121-126
159 - 195
116
123
182
412MPa (26.7)
432MPa (28tsi)
The hardness values were consistent with the observed microstructures and the equivalent
tensile strengths were derived from conversion tables.
3.9
TENSILE TESTS
Sections for tensile tests were taken from the shell of the drum, in accordance with Section
14.4.1 – Transverse tensile test and Figure 6 of BS EN 14208:2004. The results obtained are
shown in Appendix 5.
3.10
CHARPY TESTS
Sections for Charpy tests were taken from the shell and across the longitudinal weld, in
accordance with Sections 14.4.3.2; 14.4.3.3; 14.4.3.4, 14.4.3.5, Table 3 and Figure 7 in BS EN
14208:2004. The tests were carried out at 200C, 00C and -200C. The results are shown in
Appendix 6.
3.11
CHEMICAL ANALYSIS
A piece from each of the shell plate and two end plates were sent to Sheffield Testing
Laboratories for chemical analysis. The results are shown in Appendix 7.
17
Table 8 Comparison of chemical analysis of the drum plates with BS1501-151,
BS1501-161 steels
Element
Carbon
Silicon
Manganese
Phosphorus
Sulphur
Chromium
Molybdenum
Nickel
Copper
Shell
0.18
<0.02
0.63
0.032
0.039
0.02
<0.02
0.04
0.02
Open end
0.22
<0.02
0.64
0.056
0.023
0.03
<0.02
0.07
0.02
Closed end
0.20
<0.02
0.64
0.039
0.022
0.03
<0.02
0.04
0.02
BS 1501-151
0.25max
0.050
0.050
0.25max
0.15max
0.40max
0.40max
BS1501-161
0.25max
0.10-0.35
0.50min
0.050max
0.050max
0.25max
0.15max
0.40max
0.40max
The steel specifications were taken from BS1501 – 1506:1958 “Steels for use in the chemical,
petroleum and allied industries. Table 8 gives the results of the analyses on the shell and two
end plates from drum 2 and shows the specified compositions for two steels from BS1501.
The material that the shell had been manufactured from was consistent with steel to BS 1501151 B. If the steel specification was the same as that given in GC 107 for the shell and the end
plates ie BS 1501 –161 grades B or C, then this drum had also been manufactured from the
wrong grade of steel.
The paperwork for Drum 1 ie. document GC107 dated July 1959 states that the material for the
plate for the shell and ends should be BS1501-161 Grade B or C, or, BS14 flanging and welding
quality. The test sheets for the plates used for the drum quote BS1501-151 Grade B.
The specifications for BS1501-151 and BS1501-161 are almost identical except that BS1501161 steels are silicon killed and have a minimum manganese content, otherwise all the elements
are to a maximum only. For BS1501-161 the silicon levels should be between 0.10% min. and
0.35% max, and the manganese has a minimum value of 0.50%. From this it can be seen that
analyses of the plates from Drum 1 do not meet the requirements of the specification for
BS1510-161 steel as the silicon levels are below the 0.10% minimum specified. They do,
however, meet the requirements for BS1501-151 steel.
The phosphorus level in the open end plate steel was 0.056% ie. it was above the level of
0.050% maximum specified in the standard.
3.12
RADIOGRAPHY AND ULTRASONICS OF DRUM ENDS
The two drum ends were sent to an outside NDT contractor for radiographic and ultrasonic
examination of the circumferential welds to determine if the extension features observed on the
microsections of the circumferential welds occurred only at those random positions or were part
of a defect that extended for some distance around the circumference possibly with a much
larger extension.
As with drum 1 radiographic examination revealed a large number of small welding anomalies
such as inclusions, gas pores, worm holes and weld root and profile problems. The results are
contained in Appendix 8.
Ultrasonic examination revealed a crack-like indication in the open-end circumferential weld,
some distance from the position at which the extensions were observed on the microsections. A
section containing this indication was marked on the drum circumference for further
examination.
18
3.13
BOUNDARY ELEMENT MAP
Boundary element stress analysis has been carried out by my colleague Dr J Hobbs to show the
stresses at the join between the shell and an end plate in a drum with the wall thickness of drum
2. The work will be reported in full by Dr Hobbs elsewhere. The boundary element map
obtained is included in Appendix 9 of this report to show that there are significant stresses at the
join, and, this along with the presence of small indications at the weld root at the join of these
two plates is cause for concern.
19
4
ASSESSMENT
The small weld root defects observed in the microsections were discovered by random sampling
of the circumferential welds at each end of the two drums. Some of the defects observed
appeared to have a small extension to the end of the defects that were in the weld metal. All of
the extensions were in a direction that indicated a possible fatigue element to the extension of
these defects. After breaking open a section from each drum numerous corrosion filled inroads
were visible on the section from drum 1, however, on the section from drum 2 the corroded
areas were more ‘thumbnail’ in shape indicating more fatigue like features.
The wall thickness of the shell on each drum was measured. The information supplied for drum
1, ie, the specification GC107 dated 1959 gave wall thickness calculations for the cylindrical
shell section. There were two formulae given and the wall thickness (of drum 1) should not be
less that the greater value of each of the formulae. One formula gave the thickness as 3.742mm
and the other formula gave the thickness as 6.6mm. Comparing these calculated values with the
wall thickness measurements made ultrasonically showed that some readings were as low as
6.1mm. 10 readings out of the 40 taken had values less than 6.6mm, and, 17 readings out of 40
had values of 6.6mm or less. Therefore using the calculated wall thickness, drum 1 should be
withdrawn from service, as its wall thickness is now less than 6.6mm in a number of areas. A
similar analysis carried out on drum 2 gave a calculated minimum wall thickness of 11.1mm.All
of the readings made were above this minimum wall thickness there were, however, four
readings at 11.2/11.3mm which indicate that the thickness of the drum would need to be
rechecked at the following “time of fill inspections”.
A number of dents were observed on Drum 1. The depth and dimensions of the drum were
measured and the criteria for new drums manufactured to BSEN 14208: 2004 ‘Transportable
gas cylinders – Specification for welded pressure drums up to 1000 litre capacity for the
transport of gases – Design and construction’, was used to determine if the indentations in the
old drum were such that it could remain in service with the dents repaired or if it needed to be
scrapped.
Two of the dents were deeper than the 1% of the outside diameter used to determine whether a
depression was a dent or not. Neither of the dents were greater in depth than 3% of the outside
diameter, but, when the diameter of the dent is less than 15 times its depth criteria was applied
then both dents had a dimension in the circumferential direction smaller than this figure. This
may give an indication that consideration should be given to removing the drum from service.
Three of the dents observed on the outside of the drum were in a line around the circumference;
these dents could be seen on the inside of the drum when it was examined.
The tensile test results for drum 1corresponded well with the results of the tensile tests carried
out on the as supplied parent metal. The results obtained show that there does not appear to have
been any alteration in the tensile properties of the steel during its forty years in service. The
tensile properties meet the requirements for BS1501-161 grade B steel.
No Charpy impact test requirements were indicated on the specification GC107 for drum 1,
however Izod impact figures were specified as follows: in the temperature range 150C to 250C
Izod valves were 25ft.lbs. for sample size 10x10mm or 8ft.lbs. for sample size 10x5mm. In
current texts Izod tests are not used and all impact data refers to Charpy tests, and, in one text
from 1970’s, states that Izod test values cannot be used for design purposes, which gives a
reason for the reduction in popularity of Izod testing in modern times.
20
The impact results obtained were satisfactory, when compared with BSEN 14208:2004, for the
parent metal of drum 1 at all three temperatures but the impact results taken of the weld metal
were lower at 15J (-200C), 18J (00C) and 26J (200C). On comparing these impact values with
BSEN14208:2004 Table 3 in Section 14.4.3.5 for an outside drum diameter greater than 140mm
(where the average of three specimens shall meet the impact values of 20J/cm2 in both the
parent and weld metal), it can be seen that the impact values at both -200C and 00C fail to meet
the requirements of the standard. The impact values at both -200C and 00C also both fail to meet
the requirements of PD5500: 2003 Table D2 in Annex D Section D.6.2 of 19J for10x5mm test
pieces.
However, the Charpy impact results for the parent metal of drum 2 were not satisfactory as the
impact value at -200C was 8J. On comparing these valves with BSEN 14208: 2004 Table 3 in
Section 14.4.3.5 for an outside drum diameter greater than 140mm then the average of three
specimens shall meet the impact values of 20J/cm2 in both the parent metal and weld material.
The -200C impact value, in the parent metal in drum 2, does not meet this requirement. The
impact value at -200C also fails to meet the requirements of PD5500: 2003 Table D2 in Annex
D, Section D.6.2.
Chemical analysis samples were taken from the shell and two end plates of each drum. The
paperwork for drum 1, specification GC 107 dated July 1959, stated that the material for the
shell and the end plates should be BS1501 – 161 Grade B or C, or, BS14 flanging and welding
quality. However the test sheets for the plates used for drum 1 quoted BS1501-151 grade B.
The analysis for drum 1 showed that it met the analysis requirements for BS1501-151 but it did
not meet the requirements for BS1501-161 steel. The analyses for these two steels are almost
identical except that BS1501-161 steels are silicon killed and have a silicon content between
0.1% minimum and 0.35% maximum, and minimum manganese content was also quoted. The
analysis carried out showed a silicon content in the drum plate material of <0.02%, ie below the
minimum of 0.1% specified for BS1501-161 steels. The analysis for drum 2 also showed the
low silicon content of the plates from which the drum had been manufactured, indicating that
this drum also appeared to have been made from BS1501-151 steel, however, the actual steel
from which it should have been made is unknown.
The silicon addition, to kill the steel, leads to an improvement of the low temperature toughness
and ductility; it also improves the creep strength of steels (more commonly used for boiler steels
for better creep strength).
The phosphorus and sulphur content of these steels is also much higher than the levels seen in
the modern alternatives of these steels. The lower phosphorus and sulphur contents lead to an
improved ductility. Phosphorus strengthens low carbon steel (maximum 0.2% carbon) without
inducing cold brittleness. High levels of phosphorus and sulphur reduce the fatigue life.
The microsections taken from the shell and end plates of both drums showed a large number of
inclusions, many in stringer form. The amount of inclusion material observed in these
microsections was much greater than that which would be seen in a modern equivalent of the
steels used for manufacture. It was also noted that the inclusions were elongated in both the
transverse and longitudinal sections taken from the shell plate of each drum indicating that the
plates used to manufacture these drums had probably been cross rolled.
The end plates on drum 1 were thicker than the plate used to manufacture the shell. After
performing hardness tests on the microsections from each end of the drum, both of which
contained sections of the shell and the relevant end plate, it was shown that both end plates were
harder than the shell plate by a maximum 55 Vickers points and a minimum of 30 Vickers
21
hardness points. One reason for the difference in hardness could be that the end plates were bent
to fit into the end of the shell and this may have caused some work hardening. However the
drum specification GC107 states that the drum should be stress relieved after construction,
therefore any effect of the work hardening should have been removed. Another reason for the
difference in hardness was that the end plates had been made of slightly thicker plate material
and it might be possible that insufficient time had been given for the end plates to reach the
required temperature and therefore the thermal stress relief had been less effective in the end
plate.
The internal examination of the drums is difficult to carry out especially if the studs remain in
position. No problems could be observed with the gap between the shell of the drum and the
closed end plate, however it must be noted that this gap was approximately 2m from the
viewing position and relied upon the illumination from the torch. No indication of any problems
could be detected visually in the 15mm to 25mm length (depending on the drum) where the two
plates touched each other adjacent to the circumferential weld root. Therefore reliance would
need to be placed on external NDT to determine if there were any defects in this area.
The internal surface of approximately two thirds to three quarters of the length of the
longitudinal weld could be observed through the holes, and this appeared to be satisfactory.
However NO assessment could be made of the remaining length of the longitudinal weld or the
gap between the shell of the drum and the end plate through which the interior was being
viewed, as there was no suitable way of looking backwards to see these areas. The use of an
endoscope would help considerably in viewing the interior of the drum, but there could still be
some difficulties with viewing the gap where the two plates touched each other adjacent to the
circumferential weld.
Using BS470: 1984 ‘Specification for inspection, access and entry openings for pressure
vessels’ Table 2, for vessels with an internal diameter >450mm and up to 800mm and over
2000mm length of cylindrical section, then the minimum number and type of opening should be
0 sightholes, OR 3 handholes, OR 1 headhole OR 1 manhole. From section 5.2 of the standard
all the parts that require inspection by means of sightholes and handholes should be within
1200mm and headholes within a distance of 1700mm unless suitable optical devices such as
fibre optic probes are used. From section 4.2 the minimum diameter for a sighthole for a vessel
above 300mm in diameter should be 50mm. From this information from the standard it can be
deduced that the two 42mm holes in the one end of the drums are insufficient to examine the
inside surface of the drum thoroughly unless suitable optical devices are used.
The studs around the valve holes on drum 1were in good condition with no corrosion product
present and the threads were clean and undamaged. The studs on Drum 2, however, showed a
heavy corrosion product on them. The central unthreaded part of the stud had a heavy corrosion
product on it and the corrosion product completely filled the adjacent threads where the spring
washer had been positioned. The nuts remained attached to four of the studs removed from this
drum, they appeared to be corroded in position.
Radiography and ultrasonic testing was carried out on the circumferential welds at the ends of
both drums by and NDT contractor. BSEN 14208:2004 states that the acceptance criteria for
radiographs taken of the welds shall be as specified to level C in BSENISO 5817:2003. If the
limits for imperfections in BSENISO 5817 :2003, Table 1, to quality level C (intermediate) are
applied, then the lack of fusion noted in the radiography/ultrasonic results on Drums 1 and 2 is
NOT permitted. This also applies if the lack of fusion noted is compared with PD 5500: 2003
Table 5.7-1 Radiographic acceptance levels.
22
If the limits for imperfections at quality level C from BSENISO 5817 are applied to the other
weld defects noted on the circumferential welds then the incompletely filled groove noted on the
open end circumferential weld of drum 2 would not be permitted when compared against
BSENISO 5817:2003 Table 1 –Limits for imperfections at imperfection no.1.14 and at level C.
The measured depth of the incompletely filled groove was 1.6mm but the standard allows 1mm
maximum. The circumferential weld on the open end of drum 2 also showed a larger weld
profile than diametrically opposite and on the other circumferential weld, on comparing this
with imperfection 1.9 in Table 1-Limits for imperfections from BSENISO 5817:2003, and
performing the calculation under quality level C, the weld bead is acceptable at this position.
Table 1 in BSENISO 5817:2003 gives the maximum height or width as 7mm and the calculated
value was 4.06mm.
23
5
CRITERIA AND RECOMMENDATIONS
This section suggests criteria for the examination of ageing pressure drums to determine if they
would be suitable to remain in service, based on the requirements of the relevant modern
standards.
Non-destructive tests
6.1 Thickness survey of the shell of the drum to show any thinned areas. On a drum of
approximately 750mm in diameter by 2100mm long a regular grid should be produced to give a
minimum of 40 thickness readings. If the original specification is available for the drum then
the wall thickness calculations can be carried out and the results of the calculated wall thickness
compared with the actual measured wall thickness to determine if the drum can remain in
service or needs to be withdrawn.
6.2 Analysis of any indentations in the shell needs to be carried out to the requirements of Table
A1, in Appendix A, of BSEN 14208: 2004 ‘Transportable gas cylinders – Specification for
welded pressure drums up to 1000 litre capacity for the transport of gases – Design and
construction’. This gives a method of determining if an indentation is a dent and criteria for the
repair or scrapping of new drums that can be applied to older drums also.
6.3 Examination of the circumferential weld profile to determine if the weld bead profile is a
cause for concern. Drum 2 showed a poor weld profile for half of the circumferential weld, the
weld bead was substantially larger in this area than for the remainder of the weld and showed an
incompletely filled groove at the weld toe, this can be assessed against BSEN 5817, Table 1,
quality level C.
6.4 Spark testing the drum shell to determine if the silicon killed steel specified in GC107 had
been used. This in itself causes problems as a ‘local hard-spot’ may be produced where the
analysis is carried out and the drum would need to be re-heat treated to remove the effects of the
spark test.
6.5 Radiography and ultrasonic testing can be used to determine the integrity of the
circumferential welds. This will probably need to be carried out by an experienced NDT
specialist as some design of the method needs to be made to make sure that defects are picked
up in any deleterious direction. An inspection should be carried out on the curved surface of the
dished end to find any defects that are present at the root of the weld/ end of the gap between the
two plates. The results should be assessed against BSEN 5817, Table 1, quality level C.
6.6 Internal visual examination is difficult and up to one third of the drum could not be
inspected without the aid of mirrors. Its value is also limited. The gap between the two plates
adjacent to the weld root is impossible to examine as the sides of the two plates are in close
contact for 15mm to 25 mm at this point. It is possible for there to be serious corrosion in this
region that would probably remain undetected on visual examination.
Destructive tests
6.7 If the drums can be related to their original batch on manufacture then it might be reasonable
to use a statistically significant number to check on the material specification, inclusion content,
heat treatment, hardness, tensile properties and cold temperature properties of all the plates used
to construct these drums and if ALL aspects of the testing on these drums is satisfactory then
this could be used as a basis to determine the existing life of the remaining drums in the batch.
24
However, whereas the tensile properties of the material can be deduced from the hardness test
results using conversion tables, there are no such correlations for Charpy test results. Charpy
tests have to be carried out on each individual material to determine their valve and this would
mean that to determine the cold temperature properties of the drum it would be necessary to
destroy the drum to take the material for the Charpy tests. In general Charpy test values appear
to be required for any extension of life calculations that may be made, in particular if BS7910
and PD5500 are used for the calculations.
6.8 Metallographic examination, by cutting sections from the drum, would provide information
on the inclusion content of the steel and whether this was in a deleterious form, whether the
microstructure was correct, it would allow the weld bead to be assessed, and, hardness tests
could be carried out. The microstructure and the hardness tests would both give an indication if
the correct heat treatment had been given to the various plates that made up the drum. It would
also allow for chemical analysis, tensile tests and Charpy test pieces to be removed from the
drum.
25
6
CONCLUSIONS
7.1 Drum 1 had been manufactured from steel not specified on the drum specification document
GC107. The steel that should have been used had a silicon addition that leads to an
improvement in the low temperature properties of the steel.
7.2 The Charpy values obtained on testing samples from both drums were below the values
required in current standards at –200C, in the weld metal on Drum 1and in the parent plate on
Drum 2. The Charpy result at 00C in the weld on drum 1 was also below the required level.
7.3 The analysis of the steels showed high phosphorus and sulphur levels. The lower
phosphorus and sulphur levels in modern steels gives improved ductility whereas the higher
levels of phosphorus and sulphur lower fatigue life, therefore the fatigue life of these old drums
must be considered suspect.
7.4 The circumferential weld at each end of the drums was used as a ‘rolling band’ poor weld
profiles could affect the stresses that the circumferential weld undergoes when moved using
these bands. One half of the weld circumference on drum 2 showed a large weld bead that
showed incomplete fill at the weld toe.
7.5 Internal examination of the drums was difficult due to the restricted viewing holes at one
end where the valve would be fitted. Only approximately ⅔ to ¾ of the length of the
longitudinal weld could be observed and no assessment could be made of gap between the shell
and the end plate through which the interior was being viewed. Therefore no effective internal
examination was possible, without the aid of mirrors and an endoscope.
7.6 This design of drum, with the circumferentially welded dishes ends where the sides of the
shell and end plates touch each other for approximately 15 to 25mm adjacent to the root of the
weld, make it impossible to examine the gap between the two plates for corrosion or other
problems.
7.7 The calculated minimum wall thickness of drum 1 was 6.6mm; thickness measurements
carried out on drum 1 revealed that it had a thickness of less than 6.6mm at 17 out of 40
readings. This indicates that the drum should be withdrawn from service.
7.8 Radiography and ultrasonic testing of the circumferential weld on each drum revealed
numerous weld defects around the circumferential weld at each end of each drum. Typical
defects noted were lack of fusion, gas pores, blowholes and poor weld bead and root profiles.
Comparison with BSENISO 5817 indicates that the drums should be withdrawn from service
due to the presence of the lack of fusion indicated by the radiography.
7.9 The inclusion content in the plates that made up each drum was far higher and in a generally
more deleterious form than the inclusion content in modern steels.
26
7
REFERENCES
GC 107 July 1959 Fusion welded mild steel drums for non-toxic or low toxicity low pressure
liquefied gases
BS EN 14208 :2004 “Transportable gas cylinders. – Specification for welded pressure drums up
to 1000 litre capacity for the transport of gases. – Design and construction”
BS 1501-1506:1958 “Steels for use in the chemical, petroleum and allied industries”
BS 7910:1999 “Guide on methods for assessing the acceptability of flaws in metallic structures”
PD5500: 2003 “Specification for unfired fusion welded pressure vessels”
HS(G)93 The assessment of pressure vessels operating at low temperature
BSENISO 5817: 2003 “Welding – Fusion-welded joints in steel, nickel, titanium and their
alloys (beam welding excluded) – Quality levels for imperfections”
27
Neg. No. 0401-107/13
Figure 1 Drum 1
Neg. No. 0401-107/15
Figure 2 Open end of drum 1
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
28
Neg. No. 0401-107/16
Figure 3 Closed end of drum 1
Neg. No. 0401-107/58
Figure 4 Drum 1 longitudinal weld
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
29
Neg. No. 0409-046/1
Figure 5 Drum 1 dent at position 32
Neg. No. 0409-046/14
Figure 6 Drum 1 internal view of dent at position 32
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
30
Neg. No. 0409-046/3
Figure 7 Drum1 dent at position 12
Neg. No. 0409-046/5
Figure 8 Drum 1 depth of dent at position 12
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
31
Neg. No. 0506-031/64
Figure 9 Drum1 internal view of dent at position 12
Neg. No. 0409-046/8
Figure 10 Drum 1 dent at position 13
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
32
Neg. No. 0409-046/2
Figure 11 Drum 1 dent at position 11
X3.7
Figure 12 Drum 1 section across open end weld
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
33
X 200
Figure 13 Drum inclusions present in the shell plate
X 200
Figure 14 Drum 1 inclusions present in end plate
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
34
X 3.4
Figure 15 Drum 1 section across weld at closed end
x200
Figure 16 Drum 1 inclusions in the closed end plate
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
35
X 3.7
Figure 17 Drum 1 section across longitudinal weld
X 200
Figure 18 Drum 1 shell microstructure
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
36
x 200
Figure 19 Drum 1 microstructure in open end plate
X 200
Figure 20 Drum 1 closed end plate
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
37
x200
Figure 21 Drum 1 inclusions in longitudinal microsection
X 200
Figure 22 Drum 1 inclusions in transverse microsection
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
38
X 2.8
Figure 23 Drum 1 defect as first observed
X 50
Figure 24 Drum 1 defect after preparation
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
39
Figure 25 Drum 1 indications after breaking open
X 10
X 100
Figure 26 Drum 1 planar defect
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
40
Neg. No. 0406-027/2
Figure 27 Drum 2
Neg. No. 0406-027/13
Figure 28 Drum 2 raised weld bead at one end of drum
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
41
Neg. No. 05406-027/4
Figure 29 Drum 2 open end
Neg. No. 0406-027/9
Figure 30 Drum 2 closed end
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
42
Neg. No. 0406-027/26
Figure 31 Drum 2 score marks on surface
Neg. No. 0406-027/24
Figure 32 Drum 2 score marks
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
43
Neg. No. 0209-060/3
Figure 33 Drum 2 studs
Neg. No. 0209-060/12
Figure 34 Drum 2 stud removed from drum
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
44
Neg. No. 0502-020/4
Figure 35 Drum 2 weld bead with large profile
Neg. No. 0502-020/23
Figure 36 Drum 2 weld bead on remainder of weld
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
45
Neg. No. 0410-073/4
Figure 37 Drum 2 section across poor weld profile at open end
X 100
Figure 38 Drum 2 small extension at weld root
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
46
Neg. No. 0410-073/6
Figure 39 Drum 2 better weld profile on open end
X 100
Figure 40 Drum 2 small extension at weld root
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
47
Neg. No. 0410-073/2
Figure 41 Drum 2 section across weld at closed end
X 100
Figure 42 Drum 2 small extension at root of weld
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
48
Neg. No. 0410-073/7
Figure 43 Drum 2 across longitudinal weld
x100
Figure 44 Drum 2 shell microstucture
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
49
X 100
Figure 45 Drum 2 microstructure in open end plate
X 100
Figure 46 Drum 2 microstructure in closed end plate
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
50
X 200
Figure 47 Drum 2 inclusions in longitudinal microsection
X 200
Figure 48 Drum 2 inclusions in transverse direction
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
51
X 6.7
Figure 49 Drum 2 indications after breaking open
X 50
Figure 50 Drum 2 pits detected on ultrasonic testing
© Crown Copyright
HEALTH AND SAFETY LABORATORY
An agency of the Health and Safety Executive
52
8
APPENDICES
53
8.1
APPENDIX1 - TENSILE TESTS DRUM 1
54
55
56
8.2
APPENDIX 2 – CHARPY TESTS DRUM 1
57
58
59
60
8.3
APPENDIX 3 – CHEMICAL ANALYSIS DRUM 1
61
8.4
APPENDIX 4 – NDT REPORTS DRUM 1
62
63
64
65
8.5
APPENDIX 5 - TENSILE TESTS DRUM 2
66
67
68
8.6
APPENDIX 6 – CHARPY DRUM 2
69
70
8.7
APPENDIX 7 – CHEMICAL ANALYSIS DRUM 2
71
72
73
8.8
APPENDIX 8 – NDT REPORTS DRUM 2
74
75
76
8.9
APPENDIX 9 – BOUNDARY ELEMENT MAP OF JOIN BETWEEN
SHELL AND END PLATE
77