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A welder at the supply house changed my mind about pre-heating small repairs

I was grabbing some 7018 and overheard him telling another guy that skipping pre-heat on a 3/8 inch patch for a feedwater heater was why his weld cracked after a month. I always thought that was just for the big, thick stuff. Now I'm rethinking my whole approach for anything over a quarter inch. Anyone have a good rule of thumb for when you absolutely need to break out the rosebud?
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3 Comments
torres.blair
So what's his actual pre-heat method?
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pat_murray53
He actually pre-heats for way longer than most people. It's a full hour at a low temp before cranking it up. That slow ramp seems to be the key to avoiding cracks.
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fiona_kim97
Heard a similar story about a cracked trailer hitch.
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