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Fabrication
Figure 4. General view of E-02A tubesheet cross section after cutting at CS02.
Open of these cases, the affected units were removed from service while operations continued with the remaining two exchangers. The heat exchangers in these reports shared common characteristics: they were fabricated in accordance with recognised design codes such as ASME Section VIII, BS PD5500, constructed using 2¼Cr-1Mo low alloy materials and operating in high-temperature, high-pressure hydrogen environments.
Examined location # 4 OD
Replicated micrographs at 50X( left) and 200X( right)
Figure 5. Cross section view of crack through the thickness( top). Replica test image at magnification of 50x( bottom left) and 200x( bottom right) showing crack propagation in intergranular manner.
These repeated observations suggest that the issue is not plant-specific but rather a systemic concern associated with this type of equipment design, fabrication and service condition.
Findings E-02A was transported to a fabrication shop, where it was fully sectioned through its CS02 weld joint to expose the cracks and facilitate a comprehensive examination, as shown in Figure 4. Hardness testing was conducted on the weld and base metal from both the internal and external surfaces of E-02A. The results showed elevated hardness values on the internal areas of weld, ranging from 241 to 345 HB, exceeding the recommended maximum of 225 HB as outlined in API 934-A. In contrast, the base metal exhibited normal hardness readings of 150 to 168 HB on the external surface and 132 to 192 HB internally. Replica metallography and other NDE confirmed that the cracks propagated in an intergranular pattern across the weld region, with some progressing through the full wall thickness as shown in Figure 5. The cracked areas at the weld joint of the tubesheet also revealed numerous intergranular fissures in the vicinity of the identified cracks especially at the weld and heat affected zone( HAZ) regions. The findings indicate that high hardness remained in the weld region due to insufficient post-weld heat treatment( PWHT) during fabrication. Specifically, local PWHT was applied externally using heating pads, but no internal thermocouples were used to verify adequacy to the required temperature and holding time. Given the substantial wall thickness, and the vicinity to heavy components such as the tubesheet, heat sinking likely occurred, reducing the effectiveness of PWHT. The high hardness, coupled with residual stresses and other factors such as elevated pressure, temperature gradients, complex geometry, and hydrogen exposure, likely initiated and propagated the cracks observed during inspection.
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