TPi March 2019

Tube welding technology

Weld purging heat-treated pipes New power plants are in high demand, and several hundred are expected to be built over the next decade. Chromium- molybdenum (chromoly) steel pipe such as P91 is a major construction material for the high-pressure piping in these plants, and there are particular techniques for welding this pipework to avoid potential problems caused by oxidation. be welded with a shield of inert gas, both inside and outside the pipe joint. It is not practical or cost-effective to fill the whole pipe with inert gas. Restricting the weld purging zone has proven most effective, so dams either side and close to the weld joint are often used. It has been common in the past to use dams made of cardboard. However, that material contains water vapour and oxygen, which is released into the weld zone as the weld progresses.

Huntingdon Fusion Techniques (HFT) for heat-treated chrome and high- strength stainless steel pipe joints where the temperatures might be as high as 760°C (1,400°F) for many hours. HotPurge allows the purge to be safely continued for up to 24 hours while pre-heating, welding and post-weld heat-treating with the purge system remaining in place. HotPurge includes the PurgeGate ® device to prevent over-inflation of the dams. No matter how high the user increases the pressure to deliver more gas flow, PurgeGate prevents too much pressure being delivered to the inflatable dams, allowing an increased flow to achieve a lower oxygen level or faster cooling of the weld zone. Huntingdon Fusion Techniques – UK

Pre-heat and post-weld heat treatments are mandatory, and critical to the service life of the alloy. Chromoly is a low-alloy steel and has also been used to produce tubing for bicycle frames and race car roll cages. It is not as lightweight as aluminium alloys, but has the advantages of high tensile strength and malleability. To ensure the welds are free from oxidation, which could otherwise lead to a loss of corrosion resistance, they must

Professionally and manufactured inflatable pipe purging systems are widely used for most stainless steels and titanium. For chromoly, however, most inflatable purging systems are not suitable due to the necessary high pre-heat and post- weld heat treatment temperatures. HotPurge ® pipe purging systems have been designed and developed by designed

hft@huntingdonfusion.com www.huntingdonfusion.com

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May Issue

27 th February 2019 Editorial closing date:

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2019 Media Pack