Hydrotesting Milestone Reached in Weld Residual Stress Programme

We are pleased to share a significant milestone in our ongoing Weld Residual Stress research programme being delivered in collaboration with UK gas network operators.

Over recent weeks, the project team has successfully completed hydrostatic testing on two representative pipeline samples:

• 48-inch (1219 mm) diameter pipeline

• 6-inch (168 mm) diameter pipeline

These samples represent the largest and smallest pipeline sizes included within the test programme and form a key part of an industry-wide effort to improve understanding of weld residual stress behaviour in gas transmission assets.

Why Are We Doing This?

Current pipeline integrity assessments often assume highly conservative weld residual stress levels. While this provides a robust safety basis, it can also result in costly inspections, repairs and assessment requirements.

A key question for the industry is:

How much residual stress is actually relaxed during hydrostatic pressure testing?

To answer this, the project combines hydrostatic testing, strain monitoring, residual stress measurements and finite element modelling to generate high-quality experimental evidence.

Monitoring Stress Relaxation During Hydrotest

Prior to hydrotesting, the weld regions were instrumented with strain gauges positioned across the weld, heat affected zone (HAZ) and parent material.

During pressurisation, strain data was continuously recorded to capture the material response and identify any evidence of residual stress relaxation.

The successful completion of the hydrotests has generated an important dataset that will be used to:

• Quantify stress relaxation during hydrotesting

• Compare behaviour across different pipe sizes

• Support development of validated engineering models

• Improve confidence in future pipeline integrity assessments

What Happens Next?

With hydrotesting now complete, the project moves into the next phase:

🔹 Detailed analysis of the strain monitoring data

🔹 Residual stress measurements before and after hydrotesting

🔹 Comparison of measured stress states with current assessment assumptions

🔹 Integration of results into finite element models

The ultimate goal is to provide evidence-based guidance that supports safe and reliable operation of existing pipeline infrastructure while reducing unnecessary conservatism where appropriate.

Industry Collaboration

This project demonstrates the value of collaboration between network operators, engineering specialists and integrity experts in addressing key industry challenges.

Stress-Space is proud to be leading the residual stress measurement activities and contributing to research that could influence future approaches to pipeline integrity assessment and hydrogen network repurposing.