Steel Image Inc., Failure Analysis and Metallography 7 Innovation Drive, Suite 155, Flamborough Ontario, Canada, L9H 7H9, (289) 895-8363 IN-SITU METALLOGRAPHY OF A HIGH TEMPERATURE SHIFT CONVERTER EXAMPLE REPORT - Electronic Copy - Shane Turcott, M.A.Sc. Principal Metallurgist OVERVIEW Inspection of an ammonia plant high temperature shift converter was performed during a shutdown. The evaluation found, of the six locations evaluated, one panel to exhibit service degradation. Neigbhouring material, as close as 2” had not experienced the same degradation suggesting an issue with the degraded panel material. Further PMI was recommended of the panel. A weld crack found during NDT inspection was found to have been a hot tear having been there since original welding.
Transcript
Steel Image Inc., Failure Analysis and Metallography 7 Innovation Drive, Suite 155, Flamborough Ontario, Canada, L9H 7H9, (289) 895-8363
IN-SITU METALLOGRAPHY OF A HIGH TEMPERATURE SHIFT CONVERTER
EXAMPLE REPORT
- Electronic Copy -
Shane Turcott, M.A.Sc. Principal Metallurgist
OVERVIEW Inspection of an ammonia plant high temperature shift converter was performed during a shutdown. The evaluation found, of the six locations evaluated, one panel to exhibit service degradation. Neigbhouring material, as close as 2” had not experienced the same degradation suggesting an issue with the degraded panel material. Further PMI was recommended of the panel. A weld crack found during NDT inspection was found to have been a hot tear having been there since original welding.
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 1 of 14
IN-SITU METALLOGRAPHY OF A HIGH TEMPERATURE SHIFT CONVERTER
1.0 INTRODUCTION In-situ metallography was conducted upon a High Temperature Shift Converter (HTS) at six weld locations to assess for service degradation. The converter was made of SA 204B (½ wt% Mo) low alloy steel. During magnetic particle inspection of the vessel, a crack was found along the lower circumferential seam weld. Evaluation of this weld crack was included. The following report summarizes the observations obtained. 2.0 EXAMINATION Through the use of microscopes, examination of the steel can provide information regarding the current material condition and assess if the material had thermally degraded during service. In-situ metallography is a non-destructive method used to perform this examination on-site. Figure 1 displays the six weld locations evaluated. For the ease of reference, these locations are referred to by their numerical sequence of examination. These locations were prepared by successive grinding and polishing to a 1µm finish. The surface was then etched using 3% nital and examined at 200x magnification. Replications were made and examined under an optical microscope in laboratory conditions. Figure 2 displays Locations #1 (lower circumferential weld) and #2 (lower pedal weld). Examination of Location #1 found microstructural features typical of the as-
SUMMARY One lower pedal exhibited potential service degradation. The degradation was the result of either high temperature hydrogen attack (HTHA) or thermal degradation. No cracks, creep voids or micro-fissures were observed. As the neighbouring pedal did not exhibit degradation, this may suggest an issue with the material of the affected pedal. It is recommended that during the next inspection opportunity (a) the lower pedals be PMI’d and (b) monitored by in-situ metallography. The remainder of the five locations evaluated did not exhibit any signs of service degradation (ie. no HTHA or thermal degradation). The transverse crack on the lower circumferential weld found by MPI was a hot tear crack formed during welding. The primary tear and numerous other micro-tears were located adjacent a weld start or stop.
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 2 of 14
manufactured SA 204B steel and weld. Illustrated in Figures 3 and 4, the plate material comprised of ferrite, bainite and some pearlite. No decarburization indicative of hydrogen attack, thermal degradation or cracks/micro-fissures were observed. Location #2 did show signs of service degradation. One of the pedals adjacent the evaluated weld exhibited a significant reduction of bainite/pearlite. This could have either been from (a) high temperature hydrogen attack or (b) thermal degradation. Note that the weld and opposing side did not exhibit the same microstructural change. Figure 5 compares the structures of the two plates on either side of the pedal weld. The interpretation of this is further discussed in Section 4.0. Figure 6 displays the transverse crack at Location #3 which had been detected during magnetic particle inspection. Upon grinding and etching, it could be seen that the crack was situated at the end of a weld start or stop. Upon etching, the primary crack was found to contain high temperature oxide and exhibited an intergranular fracture path, typical of a hot tear. Numerous other fine hot tears were located in the vicinity. Therefore, the crack had formed during welding. Figures 7 and 8 display the micro-features of the hot tear crack. Locations #4 (longitudinal weld), #5 (mid-height circumferential weld) and #6 (inlet tube weld) comprised of microstructual features typical of the as-manufactured condition. No service degradation in the form of high temperature hydrogen attack, cracking or thermal degradation were observed at these locations. Figures 9-11 display Locations #4-6. 3.0 DISCUSSION One lower pedal exhibited microstructural degradation associated with service. The degradation was either (a) decarburization indicating high temperature hydrogen attack or (b) severe spheroidization from thermal degradation. The microstructure appeared to be more the latter, thermal degradation, however, decarburization indicative of HTHA could not be ruled out. Both of these scenarios seem peculiar considering the neighbouring pedal had not degraded, even though it was less than two inches away from the affected zone. This could suggest some issue with the affected pedal material, potentially a difference in the pedal chemistry. It is advised that PMI be conducted on the bottom pedals during the next opportunity. The evaluated pedal weld was immediately below the top inlet entry and, due to the grinding, should be easy to find. No cracks, creep voids or micro-fissures were observed on the affected pedal. It is advised that the pedals be closely monitored and in-situ metallography be performed during future inspection opportunities. The transverse crack at Location #3, on the lower circumferential weld, was a large hot tear formed during welding. Optical examination found the majority of the primary crack to have existed after welding. With the oxide present within the tear, it would suggest this crack had been opened to the surface after welding. Therefore, it was unclear how
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 3 of 14
this tear had not been observed during previous inspections. Ultimately, the cause of the crack was associated with an issue during manufacture and not with service degradation. No service degradation or issues were observed at the remaining four locations evaluated. 4.0 CONCLUSIONS The evaluation found one lower pedal evaluated to exhibit service degradation. The degradation was either the result of high temperature hydrogen attack or thermal degradation. In either case, no cracks, creep voids or micro-fissures had formed. The neighbouring pedal, only two inches away, did not exhibit any notable deterioration. Assuming the neighbouring vicinities experienced relatively similar operating conditions, this may suggest an issue with the material of the affected pedal. It is recommended that during the next inspection opportunity (a) the lower pedals be PMI’d and (b) monitored by in-situ metallography. The remainder of the five locations evaluated did not exhibit any signs of service degradation (ie. no HTHA or thermal degradation). The transverse crack at Location #3 on the lower circumferential weld was a hot tear crack formed during welding. The primary tear and numerous other micro-tears were located adjacent a weld start or stop.
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 4 of 14
Figure 1: Schematic displaying the locations evaluated by in-situ metallography and
hardness testing on the HTS.
Location #1 (lower circumferential
weld)
Location #2 (Pedal Weld)
Location #3 (cracked lower
circumferential weld)
Location #4 (Longitudinal Weld)
Location #5 (mid height
circumferential weld)
Location #6 (Inlet Tube Weld)
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 5 of 14
Figure 2: Photographs displaying the locations of the (1) lower circumferential weld
and (2) a pedal weld.
a) Locations #1 and #2
b) Lower Circumferential Weld, Location #1
c) Lower Pedal Weld, Location #2
Top of Circumferential Weld
(Figure 3)
Bottom of Circumferential Weld
(Figure 4)
Location #1 (lower circumferential
weld)
Location #2 (Lower Pedal Weld)
Pedal Weld (Figure 5)
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 6 of 14
Figure 3: Micrographs from the replica taken at Location #1 (lower circumferential weld) of the top edge of the weld. The base
metal, heat affected zone and weld metal were typical of the as-manufactured condition. No evidence of HTHA, cracks or thermal degradation was observed.
Ferrite, bainite and some pearlite (typical for SA 204B)
b) Base Metal, 400x c) HAZ, 400x d) Weld Metal, 400x
a) Top Weld Edge, ~75x
Base Metal Heat Affect
Zone Weld Metal
Acicular ferrite and carbides (typical for weld)
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 7 of 14
Figure 4: Micrographs from the replica taken on the bottom portion of Location #1, of the lower circumferential weld on the pedal
side. No evidence of HTHA, cracks or thermal degradation was observed.
d) Base Metal, 400x c) HAZ, 400x b) Weld Metal, 400x
Ferrite, bainite and pearlite (typical for SA 204B)
Acicular ferrite and carbides (typical for weld)
Base Metal Heat Affected Zone
Weld Metal
a) Bottom Weld Edge, ~75x
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 8 of 14
Figure 5: Micrographs of the replica taken from Location #2 of a lower pedal weld. The base
microstructure on one of the two pedal welds was not consistent with SA 204B steel. This indicated service degradation during service from either HTHA or, more likely thermal degradation. No cracks or micro-fissures were present. It is recommended that this pedal be subjected to PMI and closely monitored during future shut-downs.
b) Left Side of Pedal Weld, ~75x
c) Right Side of Pedal Weld, ~75x
a) Location #2 (Pedal Weld)
Left (Figure 5b,d)
Right (Figure 5c,e)
Base Metal (right pedal)
Weld Metal Weld Fusion
Line
Base Metal (left pedal)
Weld Metal
d) Left Pedal Base Metal, 400x e) Right Pedal Base Metal,
Degraded Structure (either decarburization from HTHA or
spheroidization from thermal degradation)
Typical for SA 204B with no service degradation
Weld Fusion Line
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 9 of 14
Figure 6: Photographs displaying the crack at Location #3 which had been detected
by magnetic particle inspection. After grinding and etching, it was found that the crack had initiated at a weld start or stop.
b) Ground & Polished
c) After Etching
Weld Start/Stop
a) Location #3 (NDT detected Crack)
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 10 of 14
Figure 7: Micrographs from the replica of Location #3 displaying numerous hot tear
cracks at the edge of the weld start/top. The hot tears were filled with high temperature oxide. These tears, and the majority of the crack, had formed during welding.
a) Location #3, Crack
c) At Start/Stop Tip, 100x
Oxide along tears (formed while weld was hot)
Numerous hot tears at weld
start/stop
b) At Start/Stop Tip, 400x
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 11 of 14
Figure 8: Micrographs displaying one end of the crack at Location #3. The crack
comprised of oxides near the end, suggesting the majority of the crack at this plane had existed after welding. Numerous, sub-surface hot-tears were also within the vicinity. No evidence of HTHA or service degradation was observed.
a) Location #3, Crack
b) Location #3, Crack End, 100x
c) Sub-Surface Hot Tears, 200x
d) Location #3, Crack End, 400x
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 12 of 14
Figure 9: Micrographs of the replication taken from Location #4, a longitudinal
weld on the bottom portion of the converter. No evidence of HTHA, cracks or thermal degradation was observed.
a) Location #4, Longitudinal Weld
b) Weld Edge, ~75x
c) Weld, 400x d) Base Metal, 400x
Heat Affected Zone
Weld Metal Base Metal
Ferrite, bainite and some pearlite (typical for SA 204B)
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 13 of 14
Figure 10: Micrographs of the replication taken from Location #5, the mid-height
circumferential weld. No evidence of HTHA, cracks or thermal degradation was observed.
a) Location #5, Mid-Height Circumferential Weld
d) Weld, 400xc) Base Metal, 400x
Heat Affected Zone
Weld Metal Base Metal
b) Weld Edge, ~75x
Ferrite, bainite and some pearlite (typical for SA 204B)
Example Report
In-Situ Metallography of a High Temperature Shift Converter Page 14 of 14
Figure 11: Micrographs of the replication taken from Location #6 at the inlet region.
No evidence of HTHA, cracks or thermal degradation was observed.
a) Location #6, Top Inlet
d) Weld, 400xc) Tube Metal, 400x
Heat Affected Zone
Weld Metal Tube Metal
b) Weld Edge, ~75x
Ferrite, bainite and some pearlite (typical for SA 204B)
