Abstract
For offshore pipeline, the System Pressure Test (SPT) is the traditional conclusion of the installation campaign and the final quality control measure. As a gross error final test, the relevance of the SPT was challenged by the REPLACE Joint Industry Project (JIP), which kicked off in 2019 with a total of 21 sponsors, bringing experience from all levels of the industry. The objective was to develop and issue a guideline detailing a systematic approach for the participants to enable them to replace the SPT. This is allowed in DNV pipeline standard, DNV-ST-F101 (2021) for selected pipelines with "extraordinary disadvantages", given that the approach maintains the same level of safety as if the SPT was performed. The guideline was completed and issued in 2020, and will be referred as JIP REPLACE (2020) in this paper.
One of the JIP activity scope was to collect description of past pipeline loss of containment that the system pressure test successfully detected and review them to identify the failure mechanisms and the associated root causes. This paper presents the assessment results of offshore pipeline system pressure test failures carried out as part of the JIP REPLACE. The review of 47 cases covering a period from 1976 to 2019, allowed identification of commonality in the failure mechanisms and type of triggering defects. The paper identified common failure properties and failure modes involved.
As the considered failures span over decades, the failures were reviewed against current DNV-ST-F101 revision, to confirm if the associated failure mechanism could have been detected and avoided by current code requirement.
The review of past failure during SPT confirmed that the DNV-ST-F101 would have been adequate to avoid or detect the failure mechanism prior to the system pressure test. Within the scope of the JIP REPLACE, this work allowed to identify commonality within the failure cases as well as trends along the years in regard of the type of failure mechanism. These failures cases constituted the basis for the establishing the set of prerequisites and requisites defined in the JIP REPLACE guideline. The prerequisites and requisites allow to assess suitable pipeline system candidate for system pressure test replacement, as such bringing learning from past industry project to future ones.
