Abstract
Pipelines are widely used in the oil and gas industry for transporting crude oil and natural gas from the field to refineries. It has been a general practice to use alternative weld flaw acceptance criteria to assess the acceptability of mechanized girth welds using an engineering critical assessment (ECA) approach. The ECA concept of defining weld flaw acceptance criteria has been accepted as a fitness for service (FFS) assessment based on fracture mechanics, which requires robust welding procedures. Effective planning of the welding procedure specification (WPS) qualification and mechanical testing of the weld and heat-affected zone (HAZ), and weld inspection are the key factors contributing to robust welding procedures and an effective ECA.
Mechanized gas metal arc welding (GMAW) processes are commonly used in pipeline girth weld welding because of their high quality and productivity. With the technical advancements of non-destructive testing (NDT) techniques, the use of automated ultrasonic testing (AUT) with supplemental time of flight diffraction (ToFD) has further enhanced the accuracy and productivity in weld inspection, weld flaw sizing, and probability of detection. The use of alternative acceptance criteria to assess the acceptability of mechanized girth welds using an FFS approach can significantly reduce the construction cost by focusing weld integrity on significant weld flaws. Consequently, unnecessary weld repairs are minimized, increasing the ability to utilize welding resources to achieve more predictable weld quality and productivity. Mechanized girth weld acceptance criteria have been progressively transitioned from using workmanship standards into FFS-based ECAs.
The semi-automatic waveform controlled GMAW and mechanized flux-cored arc welding (FCAW) processes are not unique to the pipe welding industry, especially tie-in welding. However, ECA-based weld flaw acceptance criteria have not been commonly applied to welds using the above welding process combinations. This paper focuses on the development of the alternative weld flaw acceptance criteria for mainline production girth weld construction using a hybrid of semiautomatic waveform controlled GMAW and mechanized gas-shielded FCAW (FCAW-G) processes. It explains the integration of the intended WPS qualification, mechanical testing, ECA methodology and AUT procedures. The girth weld acceptance criteria were developed based on CSA Z662-19 Annex K using Option 2 methodology. Additional fractography, metallography, and hardness mapping were conducted to characterize test specimens with crack tip opening displacement (CTOD) pop-ins.
