Distortion Control

By pipewelder_1999 (****)

Date 07-13-2001 12:02

Without knowing more specifics and aside from welding technique and sequence the following can reduce distortion

1) Restrain the joint from movement during welding. This could include restraint that keeps the centerlines of the 2 cylinders parallel and also internam or external support that minimizes the shrinking of the circumference.

NOTE: This will increase the amount of stress in the joint. Post weld heat treatment will then reduce the stress and keep the item from "springing" one the bracing/support is removed.

2) I feel preheat if uniform over the entire weldment greatly decreases distortion. Local preheat may worsen distortion if not properly applied.

I'm sorry I can't be more help. There are some very good books available from various sources that address distortion control. The welding handbook volume one has some useful information.

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

Date 07-16-2001 16:48

Further to Pipewelder's suggestions, I'd also recommend to check the threads after the weld is complete. Chances are (good chances, by the way) that the threads will suffer some warpage due to the heat input from welding, preheating etc.
Put the welded pieces in the lathe and pass the chasers carefully over the threads, using the proper lubrication.
Giovanni S. Crisi
Sao Paulo - Brazil

By Himark Date 07-22-2001 02:20

The problem is that these pieces will be installed in the field. The following pass sequence was given to me and would appreciate any comment:
(Start) 11 o'clock to 1:00;
7:00 o'clock to 5:00 o'clock;
1:00 o'clock to 3:00 o'clock;
9:00 o'clock to 7:00 o'clock;
3:00 o'clock to 5:00 o'clock;
11:00 o'clock to 9:00 o'clock (Finish).
Any welder I talked to would balk at this, but it would appear on paper that it might tend to equalize some of the stresses. Comments??

By pipewelder_1999 (****)

Date 07-22-2001 19:21

This sequence would be great for putting on a truck tire. In my opinion this sequence would cause the item to be distorted with the kink located around the 5 o'clock position.

If my thinking is correct the bulk of the residual stress and/or heat buildup is located at the stops of the welds. You would like to balance those spots around the circumference. On a mock up I would start with

11-1
5-7
9-11
3-5
7-9
1-3

One thing you can do is to monitor any distortion as you are welding and correct your sequence as needed. That may minimize the distortion but who knows. I worked in a machine shop and keeping shafts straight was done by welding oversize pcs and machining them afterwards so I may be off in left field.

Good Day

Gerald Austin