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Zinfra hot-taps into nuclear technology
Zinfra hot-taps into nuclear technology

Teaming up with the Australian Nuclear Science and Technology Organisation (ANSTO), Zinfra is using cutting-edge nuclear technology to undertake residual stress testing on a hot-tap fitting for the Northern Pipeline in Hexham, NSW.

Zinfra was engaged to provide specialist advice on a large 20” spherical tee in-service weld connection to a Class 600 gas pipeline.


The hot-tap presented unique challenges: the fitting location in a swamp required detailed Finite Element Analysis (FEA), and the fitting thickness, at > 32mm, exceeded the AS4458 Code that requires Post Weld Heat Treatment (PWHT) to be carried out. PWHT would have required the pipeline to be shut down and depressurized.


Zinfra engaged ANSTO to measure the residual stresses in a simulated thick spherical tee, both in the as-built and in the PWHT condition.

3D FEA modelling of the 20" Spherical Tee by ANSTO


Paul Grace, Engineering Manager Gas & Water at Zinfra, explained, “We wanted to understand why the Code has these limitations and to understand if the Code limitations were valid for this situation.”


The measurements were made by using non-destructive neutron diffraction technique at the OPAL reactor.  Australia’s Open Pool Australian Lightwater (OPAL) reactor is a state-of-the-art 20 Megawatt reactor that uses low enriched uranium (LEU) fuel to achieve a range of nuclear medicine, research, scientific, industrial and production goals.   


The results for the as-built hot-tap fitting found high residual stresses at the weld intersections, particularly at the weld toes and root, but were less than Code-based estimates. The residual stresses were significantly reduced after PWHT, and also lower than Code-based estimates for PWHT welds.


Site welding works also presented some challenges with dewatering required to prevent the fitting being submerged underwater.


Paul Grace will be delivering a detailed presentation about this project at the APGA Pipeline Operators Group (POG) Seminar in Brisbane on Thursday, 23 April 2015.


For more information, Paul Grace can be contacted on 0427 002 601.

On-site welding of the 20" diameter Spherical Tee