Monday, August 9, 2010

[MW:6386] Re: Flame straightening of distorted weldments

Dear Mr. Vagal,

Weld distortion is caused by shrinkage of the weld at which the
material sometimes becomes internal residual tensile stresses above
the materials yield strength. Because of that it will cause elongation
in small areas which causes the distortion. In some cases you can
straighten the structure by heating small local spots in a specific
temperature, during cooling down the material will shrink to a smaller
dimension as before the heating and therefore will cause some residual
tensile stress in the structure by which the distortion can be
reduced. But be aware, this is a very special procedure and you need
someone with a lot of experience to execute such properly. Beside that
you will also introduce extra tensile stresses into your structure
which is not desirable especially in case where fatigue can be a
problem due to dynamical loads. I know that a lot of shipyards still
use this technology for straighten there plate fields for a ship hull
after the stiffeners are welded against it but the people who execute
such are really professionals with many years of experience.

Sometimes technical gas suppliers have also such professionals
available who can support their clients to execute such, perhaps you
can contact your welding gas supplier to see if they have someone with
experience in this direction.

Best Regards,

Herman Pieper

On 9 aug, 03:42, Shashank Vagal <nach_...@yahoo.com> wrote:
> Hi members,
> During and after welding distortion due to myriad reasons (wrong welding sequences, incorrect travel speed etc) usually occurs in the weldments. There is a definite methodology to restore this distortion and bring it within the limits of dimensional tolerances. I have seen some experts in this field who just apply torch flame to bring it to red heat - some typical portions of the affected parts and then apply water as coolant and lo! the material straightens out. What is the science behind it? I guess all is done below 300 deg C as judged from the colour of the spots.
> Can some one guide me what it is all about, what factors rule here? What are the risks involved if not done properly?
> Thankfully,
> Shashank Vagal

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