Fatigue Behaviour of Lined Pipes
Status: Completed
Date Announced: December, 2010
Project reference: 21710
Summary
Carbon steel pipes mechanically lined with CRA are cheaper than clad pipe and easier and quicker to manufacture. The liner is often secured in place using weld overlay cladding at the ends. Girth welds can then be produced between sections of lined pipe in the same way as clad pipe, as the weld bevel and subsequent weld are located in the weld overlaid region.
When mechanically lined pipe is subjected to fatigue loading, there is a risk that the point at which the weld overlay interfaces with the liner (the ‘weld overlay/ liner triple point’) may be the fatigue critical detail.
Data on the fatigue strength of lined pipe with weld overlay is needed by designers during the FEED stage to allow them to specify lined pipe rather than clad pipe, and make the associated substantial savings in cost and lead time.
The ability to reliably inspect girth welds in lined pipe before installation would allow operators to have confidence in the safety of installed lined pipe, leading to increased safety and reliability of riser systems and reduced costs and lead times for sour fields.
This JIP ran from 2012 to 2014 and comprised four work packages: Measuring fatigue performance of MLP, through full scale testing, the development of an ultrasonic inspection technique for inspecting the triple point, developing approaches for engineering critical assessment (ECA) and finite element analysis to model the wrinkling behaviour of the liner.
Project Outcome
- Recommended SN curve for mechanically lined pipe in air.
- Recommendations of best practice for detecting flaws at the weld overlay/ liner interface using ultrasonics.
- Recommendations for how to analyse cracks at the weld overlay/ liner transition region using ECA.
- Estimate of the strain for the onset of liner wrinkling and a parameterised finite element model of lined pipe.