Dents and mechanical damage in pipelines can present a threat to pipeline integrity that requires proactive management. The focus of this document is on dent strain assessment and mitigating the possible initiation of a crack within the dent.
The objective of this MD-5-03 project is to develop and deliver a technical guidance document on mechanical damage engineering critical assessment (ECA) comprising a set of guidelines and assessment procedures, which pipeline operators could utilize as part of a dent ECA. The research consists of two tasks, namely, Task 1: Establish dent strain limit using...
The objective of this MD-5-03 project is to develop and deliver a technical guidance document on mechanical damage engineering critical assessment (ECA) comprising a set of guidelines and assessment procedures, which pipeline operators could utilize as part of a dent ECA. The research consists of two tasks, namely, Task 1: Establish dent strain limit using the Strain Limit Damage (SLD) method, and Task 2: Develop dent ECA procedure for dent coincident with secondary features.
As part of the Task 1 study, a literature review of the dent strain limit criterion was carried out. Then, the dent strain limit was established using the SLD method provided in API RP 1183 and adopted by Final Gas Rule [CFR 192.712(c), 2022]. Based on API RP 1183 SLD criterion (i.e., SLD=0.6 with the built-in safety factor of 1.67), a strain level of up to 12% is acceptable for dents in typical pipe steel grades. It can be used in the FFS application without compromising pipeline integrity. In Task 2, a flow chart with procedure and guidelines was developed for assessing dent with the secondary feature, followed by a detailed discussion on each flow chat element. This dent ECA procedure is specific to: (1) Dent associated with weld; (2) Dent associated with external metal loss. In addition, the effect of GW geometry on dent strain was studied, and the GW influence factor was established using FEA for various dent depths, D/t ratio, and indenter sizes, which can be utilized in assessing the strain severity of dent on the weld.