Ex. Type PWHT equipment

[gasoperations]

I am wondering if there is any Ex. Type PWHT equipment available for Pipe weld treatment in Oil & Gas process Plant.

As PWHT equipment is basically a voltage transformer to produce low voltage high current output to heat the weld joint. Therefore PWHT activity itself creates hot surface at the weld location. So logically Ex. type or Non Ex. Type equipment will not make any difference.

Any comments or suggession for this search.

Regards

 

[racookpe1978]

Your abbreviation "Ex. Type" is not clear.

Certainly not "explosive", right? "external" ???

Within power plants - which are NOT field-distant pipeline welds! - we use only electric-pad heaters, controlled by thermo-couple measurements mounted around the weld within 3 inches of the weld centerline connected directly to the power controller/data logger. 440 VAC supply, turned on and off to heatup, maintain, or cooldown at the pre-programmed degrees/minute each minute of the pre-heat-weld-PWHT sequence.

A thick weldment (1, 2, 3, or even 4-10 inches thick, 6-12-48-60 inches in diameter) can be brought completely up to temperature and maintained at that temperature (as high as 12535-1275 degrees F) using external pads. It is faster if the inside can be insulated, but not essential. The more steel that needs be heated, the more heating pads you need. The bettwe insulated you can get the steel weldment, the easier it is to heatup and maintain the heat. The PWHT cooldown rate and H/U rate will depend on thickness as well. A thin-walled pipe can easily be heated through the entire wall using electric pads.

Time to heatup, time to put on the needed blankets and their insulating wraps, number of blankets, number of thermocouples, time to cooldown, time to remove the heaters and insulation all increase as steel weight and steel size increases.

For preheat only of small welds/thin-walled welds, or maintenance of the intermediate heat while welding on smaller welds, we'll use oxy-acet. rosebud-type heaters.

 

[weldstan]

Oil and Gas processing plant contractors and operators typically use resistance heating coils for localized PWHT of welds.