I have a large ductile iron valve(48" waterway) that is in need of weld repair in the main external support rib of the valve. I am planning to use a 7018 rod and preheat to 550-750 F.and am hoping to achieve a PWHT of 850-1000 F for a period of 2-4 hrs. I have some concerns due to my limitations on PHT and PWHT. I will have to use a torch to heat the part. I can wrap the part with some weld blankets but I am afraid of a crack in the HAZ due to rapid cooling. I thought of using some type of ready heater to direct heat at the weld to try to keep the valve as hot as possible for as long as possible. Any ideas or direction to some reference material? Your stated situation and your question seems to have all the makings of a disaster in the making. It in complicated by the natural limitations implied by the background identifications, your being "Structural".A "Structural" person asking a "Welding/Heat Treating" question about a very large "Piping" component. My "Identity" up there says "Mechanical" in fact it is "Piping".You also did not say where in the world you are located, this may have a bearing on the issue.If you are in the "USA" any repair on valves is governed by "Codes" and "Standards" and is subject to inspection and re-certification. Valve repairs (even of the type you describe) are normally handled by trained, experienced and properly certified people in companies that do this all the time. I strongly recommend that you check with the proper authorities in your local area to confirm and conform with their requirements.

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