Preheat method

[vesselguy]

Welding Engineers I have met in the past have said they don't want rose-bud type oxyfuel torches for pre-heat. Of course, this is in reference to carbon steel application. I had only guess at why that is so; I surmise the reason may be because of diffulty in temperature control. Knowing there are a few welding expertens here, can you guys advise me what exactly are the reasons to not use oxyfuel rosebud torches for pre-heat? What should be used instead?

Thanks in advance.

 

[metengr]

Torch preheating is more than acceptable PROVIDED controls are in place to fan the heat out and watch, watch, watch the surface temperature of the material that is being heated.

If a vendor is going to use torches for preheat, I normally request a procedure that forces personnel to monitor temperatures and use torch tips that spread the flame versus using a cutting torch (which by the way I saw one vendor use on a field repair job at our facility).

In lieu of torches for preheat, depending on the size of the repair job, we will require electric resistance heating blankets. The reason is for the application and control of preheat also, if PWHT is required you have the equipment there and mobilized only once.

 

[vesselfab]

I can only guess that the concern is hot spots/cool spots due to lack of or excessive movement in heating source.

What we do have a fixed heat source (either rosebud or propane burner) and rotate the vessel prior to welding to get an even preheat. on longitudinal seams we do use hand held rosebuds or a long fixed propane burner.
On nozzles insertion welds we will use a propane ring or a small rosebud which is more appropriate for the size of opening.

several checks are done with a temp stick to assure entire area surrounding weld is preheated completely through metal thickness.