Abstract
Improvement of nondestructive inspection techniques has made more frequent the detection of zones containing closely spaced zones of non-metallic inclusions in pressure vessels made of low carbon steel. In the present study, closely spaced inclusions in an in-service cylindrical horizontal pressure vessel were detected by Scan-C ultrasonic inspection and considered as laminations to be assessed by Part 13 of the API 579-1/ASME FFS-1 2016 standard. The outcoming results were of rejection for Level 1 assessment, and a repair or replacement of the component was required, even though it retained a significant remaining strength. Thus, an alternative procedure to assess the mechanical integrity of pressure vessels containing zones of non-metallic inclusions is proposed with by adequation of some criteria of the API 579-1/ASME FFS-1 Part 13 standard procedure, taking into consideration the dimensioning and grouping characteristics of the inclusion zones, providing more reasonable results.
Highlights
The presence of non-metallic inclusions (NMIs) in the shell and heads of pressure vessels made of low carbon steel exposed to sour environments in the oil and gas industries is one of the main factors to increase the susceptibility of hydrogen-induced cracking (HIC)
The present research aims to adapt the FFS assessment procedure and criteria presented in Part 13 of the API 579-1/ASME FFS-1 standard to assess zones of non-metallic inclusions in pressure vessel shells made of low carbon steel
The rest of the defects have remaining strength factor (RSF) greater than 15, which indicates that the pressure vessel containing laminations as large as 16 in long and occupying as much as 60% of the thickness still retain sufficient strength to remain in service
Summary
The presence of non-metallic inclusions (NMIs) in the shell and heads of pressure vessels made of low carbon steel exposed to sour environments in the oil and gas industries is one of the main factors to increase the susceptibility of hydrogen-induced cracking (HIC). The present research aims to adapt the FFS assessment procedure and criteria presented in Part 13 of the API 579-1/ASME FFS-1 standard to assess zones of non-metallic inclusions in pressure vessel shells made of low carbon steel. Tab. 3 presents the results of Part 13 of API 579 Level 1 assessment of the zones of non-metallic inclusions listed in Tab. 2, regarding them as laminations, and evaluated according to the procedure described in section 2.2 of this paper. Lmsd ≥1.8 Dtc tmm ≥ 0.01 tc LW ≥ max 2tc , 0.1 in 0.09 max s, c Lh ≤ 0.09 max s, c tc/3 Lh ≤ min tc/3,0.5 in
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