Mar 2013
Gas Transmission
P9 Semi-Mechanised Hot Tap Welding
Mar 2013
Nov 2013
National Grid Gas Transmission
Richard Wilkinson (
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Network Innovation Allowance
Gas Transmission Networks
It is proposed to introduce a semi-mechanised welding process to complete the split-tee longitudinal seam welds in thick wall tees. A suite of welding procedures will be developed for the welding and repair of these welds in the specified materials and in all necessary welding positions.

The programme will also assess a new primary method of weld inspection ultrasonic manual phased array testing. This method will be employed and compared in conjunction with the existing methods (visual and magnetic particle) to inspect the finished welds. This will give a higher probability of the detection of weld defects and will provide enhanced confidence in weld quality.

From a safety and environmental point of view longer working hours increases the risk of occupational health hazards to the work crew due to arc radiation, fatigue, exposure to atmospheric pollutants, noise, etc. The longer the welding operation continues increases the risk of accidental damage to the in-service pipeline and increases operational constraints to the gas network.

If successful, the introduction of a semi-mechanised welding process, coupled with improved NDE weld assessment has considerable potential as it offers an innovative solution increasing the efficiency of network modifications and new customer connections.

A successful outcome to this research and development project will be the adoption of the welding and NDE techniques within National Grid’s specifications. This will allow National Grid to specify a unified welding and post weld NDE for the installation of thick wall ‘hot-tap’ tees in future projects requiring these techniques.