Establishment of Yield Strength Using Sub-Size Samples without Gas Line Shutdown, Phase 2 (Mini, full-Wall Longitudinal Specimens) – Final Report

Project Objective:
The objective of this multi-phase project was to develop, validate, and obtain regulatory acceptance for a method to establish pipeline yield strength that allows for a less expensive sampling procedure that does not require the line to be taken out of service.

Project Description:
In this project, research was conducted to develop a method where six-inch hot-tap coupons can be removed from a pipeline without interrupting service, and subsequently sent for machining and laboratory testing to determine yield strength values.

The objective is to demonstrate that sub-size samples provide the same yield strength values as traditional full-size samples.

In Phase 1, researchers evaluated three techniques for establishing yield-strength values – a partial-wall, sub-size sample and two surface micro-indentation (stress-strain probe) methods. Results indicated that material variability through the pipe wall was too great for surface techniques to be used effectively.

Phase 2 focused on validating that a full-wall, longitudinal, sub-size sample can produce results that are equivalent to – or more conservative than – a standard full-size sample. The objective of the current Phase 3 effort is to develop a methodology for statistical sampling and field verification to determine yield-strength properties for undocumented pipe.