Heat treated pipeline fittings (principally elbows, tees, and reducers) require careful process control. For example, furnace temperature, placement of the fittings in the furnace, transfer time to quenching tank, adequacy of quench or tempering time can all impact the fittings’ mechanical properties if not done properly.
In recent years, the National Energy Board (NEB) became aware of instances of quenched and tempered (Q&T) pipe and fittings having mechanical properties that did not meet Canadian Standards Association (CSA) or similar standards, being installed on pipeline systems under NEB and other regulatory bodies’ jurisdiction. In 2013, a pipeline rupture occurred on an NEB-regulated pipeline. Although failure to meet mechanical specifications was not the cause of the incident, the investigations revealed that there were fittings installed on the pipeline with yield strength of less than Specified Minimum Yield Strength (SMYS). The NEB undertook further investigations to determine if this low yield issue might indicate a systemic problem. In the cases examined, contrary to the recorded information in the Material Test Reports (MTRs), not all fittings met the specified mechanical properties requirements, and this was due to inadequate controls in the Quality Assurance Programs (QAPs) of different stakeholders. It is also important to note that MTR results based on a coupon test may not always reflect the properties of each fitting produced following that process.
The NEB has taken several actions in order to address this potential issue including:
- Issuing industry-wide Safety Advisories
- Issuing Orders to all companies under its jurisdiction
- Commissioning a third party to investigate and write a technical paper on this issue
- Hosting a technical workshop to facilitate broad dialogue between various stakeholders (using the technical paper as a seed document)
In this paper, the authors first review the manufacturing process of Q&T fittings. Then case studies are discussed involving four instances of nonconforming fittings. Lastly the authors propose solutions for different stakeholders to effect improvement in Quality Assurance (QA) of pipeline fittings. The authors also recommended enhancement of applicable clauses in related standards and initiation of several research and development (R&D) projects.