Localized heat to align bolted flange connections

By RAN Date 01-22-2008 20:17

I noticed a pipe spool that has been localized heated to aid in making up a bolted flange connection. The pipe is 10" schedule 10 stainless steel (304L). The heated areas (2) were on the heal side of pipe to 90 degree elbows. The contractors reply was that "Localized heat is used throughout the industry to stress relieve flanged connections and on pump connections. Stainless Steel welds have a tendency to pull one way or another when welded, in most cases if a fitting pulls a person can weld (called washing over) on one side or the other to straighten or correct. This particular line the men needed more pitch and did heat (localized Heat) to get more pitch on the line, they should have wire brushed the area heated afterward, we have since done so with a S.S. wire brush. The pipe and fittings were not weakened or damaged requiring replacement."
I don't buy into this response due to uncontrolled localized heating may change the chemical and physcial properties of the heated area. Comments would be greatly appreciated even though this is only an ethanol plant.

By webbcity (***)

Date 01-22-2008 21:23

RAN , use your search function , i think there has been many replies to this sort of post here in the past . maybe others will chime in . good luck . willie

By G.S.Crisi (****)

Date 01-23-2008 19:40 Edited 01-23-2008 19:51

Don't worry, RAN, back in my days of erector engineer, I've done that plenty of times and no plant busted because of that.
A word of warning, though !
You can do that on austenitic stainless steels (and 304L is one of them) and in ferritic stainless steels, because they don't change their metallurgical structure no matter the temperature changes.
You can also do that on low carbon steels because the carbon content isn't high enough to change the metallurgical structure significantly.
BUT, you can not do that on martensitic stainless steels (AISI Tp 410 is one) nor on chrome - moly low alloy steels because they'll develop a high hardness, which is harmful to the material.
Giovanni S. Crisi
Sao Paulo - Brazil

By darren

Date 01-28-2008 06:36

well if you have any serious concerns give it a pwht and get things normalized.
back charge the contractor and then next time they will get your opinion first or at least be smart enough to hide the evidence.
darren

By Kix

Date 01-28-2008 14:01

I don't have a problem with washing, but you can't tell me that when you take an oxy fuel torch or rose bud and heat the side of a stainless pipe up till it's orange and charcoals that you didn't hurt anything. I'm pretty sure this can affect corrosion resistance, but i'm not exactly sure on the 304L. I've seen this done a lot of times, but always kept my mouth shut. Your always supposed to hit it wit the wire brush afterwards or it sticks out like a sore thumb. Who cares get er done. Ever heard that before? ;-)

By mooseye (**)

Date 01-29-2008 00:42

It sounds like a bunch of shade tree welders had a hold of it.
It is not necessary to heat any metal to orange in order to make it draw. In fact, it would probably defeat the purposes.

By DaveBoyer (*****)

Date 01-30-2008 04:54

At what point do You have to become concerned about sensatization & carbide formation?