Page 52 - ITAtube Journal 2/2019

Member News
Huntingdon Fusion Techniques
Weld Purging Post Weld Heat Treated (PWHT) Pipework
HotPurge APSH PHO 10C 18 Inch
Welding processes can weaken metals by imparting residual stresses into a material, leading to a reduction in corrosion resistance properties. Post Weld Heat Treat- ment (PWHT) is regularly used to retain the strength of a metal when welding certain materials including high strength stainless steel and chromium-molybdenum (chromoly) steel such as P91.
Temperatures during PWHT might reach as high as 760oC (1,400oF) for many hours, during which time the insides of the pipes need con- tinuous purging using Pipe Weld Purging Products. Many purging materials cannot withstand these temperatures, nor resist damage during the time at temperature.
HotPurge® Pipe Purging Systems have been designed and developed by Huntingdon Fusion Techniques HFT® for Heat-Treated Chrome and
High Strength Stainless Steel Pipe Joints.
Ron Sewell, Chairman for HFT® said: “To ensure welds are free from oxidation which could other- wise lead to joint imperfections, they must be welded in an envi- ronment free from oxygen that has to be maintained during the lengthy high temperature post weld heat treatment process.”
“It is not practical or cost effec- tive to ll whole pipe lengths with Inert gas and restricting the weld purging zone has proven most effective. Argweld® HotPurge® Systems allow the purge to be safely continued for up to 24 hours whilst pre-heating, welding and post weld heat-treating with the purge system remaining in place.”
The Argweld® Tube and Pipe Purging Systems are positioned inside the pipe with one dam each side of the joint and in ated with an inert gas supply. Once a System is fully in ated and sealed in a pipe, the inert gas displaces the oxygen from within the weld purging zone ready for pre-heat- ing and welding. Each Hot- Purge® System is manufactured as standard with a Weld Purge Monitor® connection for viewing the oxygen level throughout the whole heating and welding pro- cesses.
Each HotPurge® System includes PurgeGate®, a revolutionary device to prevent over in ation of, and damage to the in atable dams. No matter how high the user increases the pressure, in order to deliver more gas ow, PurgeGate® prevents pressure rise in the in atable dams but allows an increased inert gas ow, to achieve a lower oxygen level and/ or faster cooling of the weld zone.
In addition, each HotPurge® System incorporates an innovative central band for easy positioning inside the pipe. This band, known as RootGlo®, will illuminate inside the dark pipe, for up to 20 hours, with only 10 minutes previous exposure to daylight.
HotPurge® Systems are manu- factured to suit pipe diameters from 6 to 88” (150 to 2,235 mm) and both in atable dams have pull handles securely sewn with high temperature resistant Kevlar thread that will withstand a pulling force of 1,000 lb.
These HotPurge® In atable Pipe Purging Systems can be used repeatedly for weld purging and will keep the oxygen levels below 100 parts per million (ppm) throughout the welding cycle, ensuring oxidation and coke free welds, without the metallurgical imperfections caused by exposure to too much oxygen.
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ITAtube Journal No2/May 2019
52