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Synloop Superheater Issues
PT. Kaltim Pasifik Amoniak (KPA) operates a 2000 MTPD ammonia plant in Bontang, East
Kalimantan, Indonesia. At the time of its commissioning in early 2000 it was the world’s largest
capacity ammonia plant. Between May 2002 and August 2004 two significant problems were
experienced with the Synthesis Gas (SG) Steam Superheater in the ammonia synthesis loop. The first
problem was a through-wall leak at the weld of the dished bottom head of the vessel. A crack
approximately one third of the way around the circumference was discovered in May 2002. This was
the closing weld of the vessel. Repairs were made and the condition of the seam was monitored
closely for the next two years. Repeat indications of problems at the weld seam were found and other
repairs were necessary with eventual replacement of the entire exchanger
In September 2003, leakages at 60 tube-to-tube sheet welding joints were detected by pressure test.
These 60 welds were repaired.
Unfortunately, this leakage allowed water to enter the process side during start up and shutdown
situations, which were subsequently blown into a hot downstream S-50 converter eventually
destroying its internals and necessitating complete replacement of the internals and the catalyst,
charge. However, further leakage at tube-to-tubesheet welds was found six months later and again in
the next three and a half months after repairing. Finally, the SG Steam Superheater was completely
replaced with the new one in 2005.
This paper discusses the damage seen; the root causes, and suggested design changes, which were
incorporated into a replacement vessel to avoid the re-occurrence of similar problems. Also outlined
are the results of a recent inspection that showed the new exchanger to be free of problems after two
years of steady operation
Hotdo M. Pasaribu
PT. Kaltim Pasifik Amoniak,
Bontang, East Kalimantan, Indonesia
Introduction
T. Kaltim Pasifik Amoniak is a joint
venture company owned by Mitsui and
Co. Ltd and Toyota Tsusho. Its ammonia
plant is situated in Bontang, East Kalimantan,
Indonesia, with a nominal production capacity
of 2,000 MTPD. It is an export-oriented plant
located in a remote area with an objective to
fulfill ammonia market requirements in the
world. The plant was designed and
commissioned in early 2000 by Haldor Topsoe
A/S as the process licenser and Mitsubishi
Heavy Industries, Ltd as the main EPC
contractor. Ammonia production started at the
end of March 2000.
At the time of commissioning in early 2000 it
was the world’s largest single-train ammonia
plant.
The plant operated consistently at a level higher
than its design capacity for two years before the
initial failure occurred in the synloop
superheater, E-0500.
P
111 AMMONIA TECHNICAL MANUAL2008
Brief Description of SG Steam Superheater
(E-0500)
The synthesis section of the plant uses Topsoe’s
S-250 technology. This features their S-200 and
S-50 converters in series separated by a vertical
U tube high-pressure steam superheater, which
removes reaction heat from the S-200 converter
outlet stream and adjusts the temperature for
optimum conversion in the downstream S-50
converter.
It superheats the saturated steam leaving the
main Steam Drum (V-0201). This saturated
steam is superheated to 515 °C and is used in
high-pressure steam turbines.
The steam leaving the unit has the following
specifications:
Conductivity @ 25°C <0.2 mS/cm
SiO2 <0.02 ppm
Total Iron (Fe) <0.02 ppm
This design of the superheater and it’s location
between the two synthesis converters was, to the
best of our knowledge, the first of its kind and
KPA’s experience illustrates the caution
required in operating a synloop with such
equipment located between two synthesis
converters.
Figure-1. shows the process flow of the
ammonia synthesis section of the KPA plant.
An outline of the channel section of the E-0500
superheater is shown in Figure 2 below
Main operating conditions are set out in the
process datasheet as follows
No Description Tube Side:
Synthesis Gas
Shell Side:
Steam
1 Inlet Temperature, oC 439 324
2 Outlet Temperature, oC 376 380
3 Inlet Pressure, kgf/cm2G 138 120
4 Outlet Pressure, kgf/cm2G 138 115
(Mol %) a b
H2 55.18 52.52
N2 18.39 17.51
1st Converter
R-0501
115K/G 380 oC
120K/G 324oC
SG Steam
Superheater
E-0500
138K/G 439 oC
a
138K/G 376 oC
137K/G 418oC
2nd Converter R-0502
b
324 oC
120K/G 324oC
WHB
E-0501
136K/G 340oC
304 oC
270oC
BFW Preheater E-0502
136K/G 281oC
112AMMONIA TECHNICAL MANUAL 2008
Figure-1: Process flow of ammonia synthesis loop
,
Figure-2: Outline of E-0500 channel
Materials and dimension of main components are as follows:
No Description Material Specification Dimension
1 Tube 321H SS 400 U-tubes, 38mm OD, 4.5mm t
2 Tube sheet 2.25Cr-1Mo steel 515mm t
3 Weld Overlay Inconel 600 6mm t
4 Fillet Weld Inconel 600
5 Shell 2.25Cr-1Mo steel 2086mm OD, 106mm t
6 Head 2.25Cr-1Mo steel 60mm t
Tube material was selected as 321H SS to
prevent the nitriding because the inlet
temperature of the synthesis gas is higher than
nitriding temperature of low alloy steel.
Inconel 600 overlay on the 2.25Cr-1Mo
tubesheet is also provided to avoid nitriding on
low alloy steel. The pass partition plate is made
of Incoloy 800 and prevents the shell and head
from contacting the hot inlet gas. Therefore,
shell and head material was selected by taking
into consideration the risk of nitriding and
hydrogen embrittlement/hydrogen attack
according to latest edition of Nelson curves as
referred to in API 941 standard.
The Incident and Immediate Action Taken
On May 05, 2002, during routine plant
checking, the field operator heard an abnormal
noise & smelled ammonia in the area around E-
PG
Steam 324
� 380
�
376�
439�
11m
Manhole (2.25Cr-1Mo)
Tubresheet (2.25Cr-1Mo, 515mmt)
Head (2.25Cr-1Mo, 60mmt)
Shell (2.25Cr-1Mo, 106mmt)
(2) Shell to Head
Local PWHT
2m
Outlet Nozzle (2.25Cr-1Mo)
Inlet Nozzle (2.25Cr-1Mo)
Internal (Incoloy800)
Tube (SUS321H, 38mmOD×4.5mmt)
(1) Tube to Tubesheet
Pipe (SUS347)
113 AMMONIA TECHNICAL MANUAL2008
0500 SG Steam Superheater. A high explosive
level was found within a distance of about 10-15
cm from the unit. Finally, it was determined that
the abnormal noise came from a crack at the
outer surface of the bottom hemispherical head,
located just above the manhole. The plant was
immediately shutdown.
Figure-3: Crack location
Inspection revealed that a 110 mm through-wall
crack had formed in a circumferential seam
weld while the inside weld surface showed a
crack running around approximately 1/3rd
of the
circumference of the vessel as shown in Figure-
5
As recommended by the vessel manufacturer,
the weld (identified as weld seam No. 34) was
repaired by cutting off the bottom head and
completely re-welding it back in place using the
same procedures as applied during the original
manufacturing process including re-post weld
heat treating (see Fig. 4)
On completion, the May 2002 repair was judged
a success and this equipment was re-
commissioned.
Later on, during plant normal operation the
pressure drop across the second ammonia
converter slowly started to increase. The cause
at the time was unknown. Eventually, the plant
was unable to manufacture 2000 tones/day. In
September 2003 the pressure drop across the S-
50 second converter suddenly increased to the
extent that the plant could not be operated at all
and had to be shutdown. Internal inspection of
the downstream second converter showed that
the catalyst had flowed down into the inlet pipe
(see Fig. 13).
Fortunately it was possible to run a bypass
around the S-50 ammonia converter and the
plant could be operated at 90% capacity for
some 9 months until reconstruction of the
converter was completed in July 2004. As part
of the reconstruction, the catalyst and the
internals of the converter were completely
removed and renewed. At the suggestion of the
process licensor the gas inlet piping was also
reconfigured to minimize the possibilities of
pressure drop build up during operation
Regretfully, though thorough inspection found
no indications of defects following the repair of
weld seam 34 in 2002, new cracks were found
in September 2003 and at one point a crack
penetrated the vessel wall by up to 13
millimeters. Extensive repairs to the seam were
thus made for the second time and as a
consequence, post weld heat treatment was
repeated.
During this same September shut down, it was
also decided to pressure test the tube bundle of
E-0500 (HP steam side) and the pressure test
identified 60 tube-to-tube sheet leaks (see Fig.
10). These leaks were repaired; the exchanger
Steam Outlet Steam Inlet
Syngas Inlet Syngas Outlet
Weld seam no. 34
(circumferentially crack
location)
Manhole
114AMMONIA TECHNICAL MANUAL 2008
was re-tested to confirm the repairs prior to re-
streaming.
Again, in March 2004 as a result of another
inspection (see Fig. 7), defect indications at
seam# 34 were found on which the 3rd
repair
was then carried out. However, this time the
repair method differed significantly from
previous repairs as the welding and post weld
heat treatments conditions were improved.
Smaller weld passes were applied using a
temper bead process followed by post weld heat
treatment designed to comply as closely as
possible to BS5500 requirements with
additional restrictions to endeavor to minimize
residual stresses introduced by the treatment.
The vessel was inspected again in July 2004,
after three and a half months of operation and
no significant cracking was detected. However,
in view of the fact that several post weld heat
treatment to the vessel wall had been carried
out, there was a major concern that the
hardness/strength of the base material had
dropped. Consequently, the vessel designers and
manufactures have recommended that the vessel
should be down rated to operate at a lower
pressure than the original design.
Furthermore, several preventive measures were
carried out to detect gas leakage promptly and
prevent cracks on the tube-to-tubesheet welds as
long as possible prior to complete replacement
with the new vessel in 2005.
A summary of the history of the vessel is given
in table-1.
Failure Investigation and analysis
A failure investigation was carried out to verify
the status of metallographic structures & crack
related structures to service performance and to
interpret and determine the type, cause & mode
of failure on which corrective action could be
initiated to prevent the recurrence of future
similar failures.
Those activities were conducted by the KPA
team with cooperation and support from our
metallurgical consultants, the main EPC
contractor, the vessel manufacturer, as well as
Haldor Topsoe as the process licenser.
The following damage processes were identified
1. Cracking at the heat affected zone of closing
weld 34.
2. Cracking of tube-to-tube sheet welds leading
to leakage.
3. Delamination of the cladding on the tube
sheet.
4. Nitriding of the 321 stainless steel tubes.
Following are the possibilities for the root
causes of the above failure:
Cracking at Weld 34
Characteristics of the damage
� Cracking initiated in the HAZ of weld 34 on
the inside of the vessel in both the head and
the shell side of the weld.
� Cracks ran perpendicular to the surface of
the vessel and did not follow the
microstructure. These cracks initiated in the
HAZ and then ran into the weld.
� Cracks ran circumferentially.
� Cracks were purely intergranular.
� Cracks propagated all the way through the
vessel wall and caused leakage of synthesis
gas to atmosphere.
� The vessel has contained a very significant
through wall defect and yet leaked rather
than ruptured.
� Crack propagation rate had increased.
� Cracks grew from being undetectable to near
to the maximum allowable defect size in 5
months of operation.
� Weld 34 is a closing weld that had been
locally post weld heat-treated.
115 AMMONIA TECHNICAL MANUAL2008
Possible causes
As a result of investigation, the cause of
cracking was probably due to inadequate post
weld heat treatment of a closing weld which left
the vessel with low residual stresses and then
cracking occurred as a result of hydrogen and
nitriding attack. Residual stresses can be
introduced by post weld heat treatment if high
thermal gradients are present. One major cause
could be if the temperature on the inside of the
vessel is kept hotter than the outside of the
vessel at the PWHT temperature or on cooling.
Thick nozzles were present next to weld 34 and
the pattern of cracking seen had obviously been
influenced by these nozzles. These acted as
huge heat sinks and PWHT’s given prior to
2004 had not been conducted in such a way as
to apply heat evenly to these regions. As a result
it is considered impossible for weld 34 to have
been evenly heated and cooled during the earlier
PWHTs given.
Leaking Tube-to-Tube Sheet Welds
Characteristics of the damage
� Cracks initiated at the root of the weld and
secondary cracks were present in this area.
� Cracks ran in the nickel-based weld.
� There was typically a major crack, which
was open and relatively straight.
� Secondary cracking present was multi-
branched and typical of stress corrosion
cracking.
� Small secondary cracks were filled with
corrosion product (rich in Chromium, iron
and oxygen).
� Corrosion product /deposited on the surface
of large cracks. These deposits were iron
oxide and the chromium content was very
low.
� There were deposits present at the bottom of
the crevice between the tube and the tube
sheet next to the weld that was similar to the
deposit in the major crack.
� Significant numbers of tubes leaked in E-
0500. Leaks were present in both the inlet
and outlet side of the inverted U-tube
bundle.
Possible causes
The environment required to cause cracking in
Inconel 600 type alloys is not extremely severe
and does not necessarily require any specific
contamination. The problem is often referred to
as primary water stress corrosion cracking
(PWSCC). When condensed water is formed
which then evaporates during operation a
concentration of chemicals can occur in the
bottom of the crevices formed. Therefore, the
primary cause of cracking is considered to be
stress corrosion cracking due to a significant
stress, the presence of condensed water during
shut downs, and the choice of a material which
is prone to cracking.
However, one major influential factor is also the
presence of hydrogen in the water. In the case of
E-0500, it is probable that the tubes had not
been expanded to achieve a pressure seal within
the tubesheet area so that cracks allowed
passage of synthesis gas into the steam system
when the vessel was on line and boiler feed
water into the bottom channel when the vessel
was off-line.
The cracking seen probably occurred by the
formation of a single crack, which grows
through wall. Once this had leaked through the
wall, ammonia and steam leaked through the
crack at different times. The secondary
cracking and corrosion probably then occurred.
Delamination of cladding on the tube sheet
Characteristics of the damage
� The cracks propagated along the interface
between the two materials.
� The cracks initiated at the holes in the tube
sheet.
116AMMONIA TECHNICAL MANUAL 2008
� A layer of precipitates is formed at the
interface.
� The cracks had not propagated through the
cladding
Possible causes
Delamination is only a major problem when the
cracks run through the cladding material. Where
fillet welds are applied at tubes in a tube sheet
this can be a major problem. However, if the
cladding is not stressed by surface attachments
such as fillet welds there is less driving force to
cause delamination and there is little or no
reason for cracks to run through the cladding. In
this case the cladding continues to protect the
underlying material.
In the case of E-0500 it is possible that the
delamination had been beneficial as it reduced
the stresses in the adjacent fillet welds and
probably assisted in arresting the PWSCC
cracks in them.
Therefore, the cause of delamination on the
tubesheet overlay could have been cracking due
to nitriding by synthesis gas from the tube side.
That does not occur without through wall
cracking on fillet weld
Nitriding of the 321 stainless steel tubes
Characteristics of the damage
� Nitrided layer formed on inlet tubes to a
depth of 0.2 mm (1/25th
of the wall
thickness) in 3.7 years of operation.
� Nitrided layer cracking on the ends of the
tube
Possible causes
Damage expected from the choice of materials
and the operating environment
Final Action Taken
It was finally decided to replace the existing E-
0500, as it was not safe to continue to operate
with the damaged vessel in the long term. KPA
requested the vessel manufacturer and the main
EPC contractor to review the design of the
exchanger. It was also suggested to install a
drain on the bottom channel as a preventive
measure against cracks on the tube-to-tube sheet
welds which then resulted in water
accumulation in the bottom of the process side
of the vessel. Since it could not be drained, the
wreckage of the internals of the S 50 converter
was attributed to the flushing of the
accumulated water trapped in the bottom head
of the vessel into the hot converter on a short
outage.
Based on these suggestions the re-design of the
SG Steam Superheater was carried out and
submitted to KPA who gave final their approval.
Finally, the new superheater was installed in
July 2005. This was manufactured without a
closing weld, with a fully weld overlayed
channel, with 321stainless steel tubes and with
321 welded J preparation tube-to-tube sheet
welds. The operating procedure was also revised
to ensure that no water could build up on the
process side and be blown into the S 50
converter as discussed below.
Summary of Design Improvements for E-
0500
As a result of the known issues at KPA in the E-
0500 vessel a number of options for a redesign
of the vessel were assessed. Final design
improvements are as follow,
1. Stainless fillet weld (SS347) for tube-to-
tube sheet weld and stainless overlay
(SS309L+SS347) on tube sheet was
employed instead of Inconel 600. (see Fig.
12.1)
2. Two-step PWHT was carried out for tube
sheet overlay to reduce the hardness of the
bond area.
117 AMMONIA TECHNICAL MANUAL2008
3. J groove was made for the tube-to-tube
sheet weld and the welding procedure for
the same was confirmed with a mock-up
test.
4. The bottom channel was heat treated in the
furnace as one piece after finishing all
welding.
5. A flat cover was employed instead of
spherical head for the bottom channel (see
Fig. 12.2). A drain was installed on the
bottom head so that any tube-to-tube sheet
weld leakage could be detected and drained
before establishing loop circulation.
6. Inconel overlay was carried out for the
whole inside surface of the bottom channel
including nozzles.
7. The simplified radius was used for the
corner between tube sheet and the channel
shell to avoid the stress concentration on
the Inconel 600 overlay. (see Fig.12.3)
8. Cl contamination was strictly watched
during the fabrication. Wipe test after the
washing of the drilled holes was made (the
Cl content shall be less than 0.15g/m2)
9. A sensitization test was carried out on test
coupons to simulate the stainless steel
cladding (under layer of SS309L and a top
layer SS347) on the tube sheet.
Start-up/shut-down Operation of E-0500
As a result of the lessons learned from this
experience operating procedures during
synthesis section start up and shutdown were
modified to the following. In summary
synthesis loop pressure should be always kept
higher than steam side pressures, and it must be
avoided to introduce water/steam to the
synthesis loop, during plant start-up and shut-
down
In addition, from the viewpoint of water quality,
the following should also be carried out:
1) Start-Up Operation
- Heating up condition of steam piping
and shell side of E-0500 shall be
carefully confirmed.
- Shell side of E-0500 shall be brought
on-line after the outlet temperature of
Ammonia Converter; R-0501 becomes
more than 340°C (more than dew point
of HP steam).
2) Shut-Down Operation
- In case that the synthesis section is
stopped, the inlet and outlet manual
block valves at steam line shall be closed
as soon as possible.
- Pressure of E-0500 shell side shall be
reduced to atmospheric pressure (0.2
kg/cm2G) by opening drain valve at
steam side.
A N2 purge on E-0500 shell side is
introduced on shutdown to prevent
condensation of steam and thus
eliminate the possibility of SCC due to
impurities in water.
The performance
In July 2005, the new SG Steam Superheater
was installed. In order to ensure its service
performance after running for one year, an
observation/inspection of tube-to-tube sheet
welds and weld joint #15 & #34 was carried out
during the plant shutdown in
September/October 2006. The results showed
that the vessel was in a good condition.
An external and internal inspection was also
done during the 2007 turnaround; the inspection
results by UT indicated that the new vessel had
the maximum tube expansion within 1 mm of
the back of the tube sheet so that the risk due to
the ingress of oxygen, condensation and the
concentration of contaminants during startup
that could create corrosion in the crevice can be
reduced.
Therefore, it was concluded that such equipment
was still in a good condition after two years
operation and safe for operation.
118AMMONIA TECHNICAL MANUAL 2008
Conclusions
(1) The cause of shell to head welding joint
failure was cracking by nitrogen, hydrogen
and high stress or Alkaline SCC.
High residual stress from the local PWHT
was the main cause of damage. The less
than required PWHT was probably the
result of the design of the bottom of the
vessel where large inlet, outlet, and
manway nozzles were located too close to
the subject weld. Therefore, it would be our
recommendation that no closing weld shall
be located at the bottom of the vessel (i.e.
no localized PWHT in this area).
(2) The cause of cracks on the tube-to-
tubesheet weld joint was primary water
stress corrosion cracking (PWSCC).
PWSCC normally requires condensed
water to be present. This indicates that the
cracking occurs when water is present in
the bottom of crevices around the tubes,
and any traces of chlorides could have
penetrated the tube-to-tube sheet crevices
where they would concentrate to possibly
cause the problems. This can only occur
during a start-up or a shutdown. The
presence of open major cracks and the high
rate of crack growth during shutdowns
suggests that a significant stress was
present in the fillet welds
(3) It is mandatory to ensure that crevices are
not formed at the back of the tube sheet
during fabrication with a similar design or
at least the maximum tube expansion can
be produced within 1 mm of the back of the
tube sheet to reduce the risk due to ingress
of oxygen, condensation and the
concentration of contaminants during
startup that will create corrosion in the
crevice. This resulted in intergranular
corrosion and subsequently initiation and
propagation of cracks by fatigue.
(4) It must be ensured that the heat input is
sufficient to bring the thermal mass of the
tubesheet to above the dew point of the
startup steam before steam is allowed to
enter the shell side. Prior to this steam
entry the shell side nitrogen blanking
should be maintained.
321 stainless steel will slowly nitride and
the tubes will have a limited life if there is
any significant applied or residual stress
present Austenitic stainless steels are
highly susceptible to SCC with even small
amounts of chloride and thin films of
condensed liquid
References
1. Borsig, "Failure Analysis of the Crack in
Seam 34 of the SG Steam Superheater",
dated 31 May 2002. (Confidential, not
published)
2. Firth, D., Materials Performance
Technologies Report No. 33502.02,
"Determination of maximum allowable
defect sizes and crack growth rates for weld
34 in superheater E0500", issued October
2003. (Confidential, not published)
3. Firth, D., Materials Performance
Technologies Report No 33502.06 “MPT
Examination of E-0500 Crack Samples
Taken in March 2004”, issued April 2004.
(Confidential, not published)
4. Firth, D., Materials Performance
Technologies Report No 33052.07
“Summary of the damage seen to
superheater E-0500, the possible root
causes and recommended improvements for
a new vessel”, issued April 2004.
(Confidential, not published)
5. Mitsubishi Heavy Industries Ltd, “Analysis
of Cracking in Tube to Tubesheet Welding
joint and Shell to Head Welding Joint for
KPA E-0500 Steam Superheater”, issued
May 2004. (Confidential, not published)
6. Mitsubishi Heavy Industries Ltd,
“Summary of Preventive Measures against
cracks on E-0500 SG Steam Superheater”,
119 AMMONIA TECHNICAL MANUAL2008
issued July 2004. (Confidential, not
published)
7. API Practice 941 Steels for hydrogen
service at elevated temperatures & pressure
refineries and petrochemical plants 1998.
Table-1: History of KPA vessel E -0500
120AMMONIA TECHNICAL MANUAL 2008
Figure-4: Crack location and repair work in 2002
Figure-5: Distribution of cracks in the closing welds in May 2002
121 AMMONIA TECHNICAL MANUAL2008
122AMMONIA TECHNICAL MANUAL 2008
Figure-6: Distribution of cracks in the closing welds in September 2003
Figure-7: Inside cracks indication by MT in the closing welds in 2004
123 AMMONIA TECHNICAL MANUAL2008
Figure-8: Typical crack
��� ��� ��� ��� ��� ������� ���� ����� ���� � ��� �������� ��� ����� ��� � ����� ����
Inlet side (Manhole side)
����� ����� �����Outlet side (Manhole side)
TubNo.:Row-Column
(VIEW FROM BOTTOM SIDE)
Figure-9: Penetrant Test results of E0500 tube-to-tubesheet welding joint
90�
180�
270�
0�
���������
����� �� �� �� ��������
��������
Weld Seam Tube Tube inside
indication length
��L: Linear
D:
Rounded
���
124AMMONIA TECHNICAL MANUAL 2008
Leak at the Inlet tube No 3-1 (by soap test)
Leak at the outlet tube No 13-9 (by PT)
Figure-10: Example of E-0500 tube-to-tubesheet joint leak test and PT Indications
125 AMMONIA TECHNICAL MANUAL2008
Figure-11: Distribution of leaking tube-to-tubesheet at E-0500
Figure-12.1: Material configuration on tube to tubesheet welding joint
Figure-12.2: Outline of Flat cover structure with Inconel600 overlay
Figure-12.3: Configuration of corner R on tubesheet to shell welding joint with overlay
Local PWHT
Flat cover
Furnace PWHT
Weld Overlay
(Inconel600,
5mmt)
2.25Cr-1Mo steel
106mmt Inconel 600
309L SS / 347 SS
Simplified Radius
Overlay after welding tubesheet and shell
Weld Overlay 309L SS/ 347 SS
6mmt
Fillet weld 347SS
Leg 6.6mm
515mm
50mm 309LSS
347SS Fillet weld Inconel600 Leg 4mm
Weld Overlay Inconel600
6mmt
515mm
50mm
126AMMONIA TECHNICAL MANUAL 2008
Figure-13: A big pile of Second Ammonia Converter catalyst found at inlet pipe after cutting
127 AMMONIA TECHNICAL MANUAL2008
128AMMONIA TECHNICAL MANUAL 2008