Question about pre-heating on high alloy steel welds

I keep seeing guys skip the pre-heat on P91 pipe because they're in a rush, arguing the interpass temp is enough. But the spec sheet from the mill in Gary says 400F minimum to prevent cracking. Who's right here, the old hands or the paperwork?

3 comments

3 Comments

derek_ross17d ago

Buddy of mine in Texas welded a P91 header without pre-heat last winter. They just kept the interpass temp up. It looked perfect until the hydro test. Found a hairline crack that ran six inches along the heat zone. The repair cost more than the whole job's profit. The mill sheet exists because someone already paid for that lesson.

stella11117d ago

Yeah that's a tough lesson to learn the hard way. Saw something similar on a P92 job a few years back. We got away with it once by baking the rods for a full shift first and using a digital temp reader on every pass. Still felt like rolling dice though. Now the oven and pre-heat rig are just part of the setup, no questions asked. Saves the headache later.

the_jessica17d ago

Exactly, @derek_ross. That spec is just the price of the last guy's mistake.