RE: [MW:6701] Flame straightening of distorted weldments

following is an extract from Shell DEP

FINAL CORRECTIONS

the following correction methods are acceptable, if approved by the Principal:

1. Local heating or cooling;

2. Application of force with local heating.

The following restrictions apply to the heating, cooling and forcing of piping made from carbon steel, low alloy steel or austenitic stainless steel:

For carbon steel which does not require a PWHT, the maximum temperature during alignment corrections shall be 600 °C. Temperature-indicating crayons or contact thermometers shall be used to measure the maximum temperature. If temperature indicating crayons are used, a margin of 50 °C shall be taken to allow for measurement inaccuracy, i.e., the reading with the crayon shall not exceed 550 °C. Forcing may be applied if necessary. Cooling in still air shall be applied.

For carbon steel which requires a PWHT, the maximum temperature during alignment corrections shall be the maximum PWHT temperature. Temperature indicating crayons or contact thermometers shall be used to measure the maximum temperature. If temperature-indicating crayons are used, a margin of 50 °C shall be taken to allow for measurement inaccuracy, i.e., the reading with the crayon shall not exceed the maximum PWHT temperature minus 50 °C. Only heating with application of local force shall be used and no quenching shall be used. The area shall either be heated in full compliance with the PWHT procedure or the area which is heated (and corrected) shall be post weld heat-treated.

For 0.5 Mo and Cr-Mo steels, the maximum temperature during alignment corrections shall be the maximum PWHT temperature. Preferably, contact thermometers shall be used to measure the maximum temperature, but temperature-indicating crayons may also be used. If temperature-indicating crayons are used, a margin of 50 °C shall be taken to allow for measurement inaccuracy, i.e., the reading with the crayon shall not exceed the maximum PWHT temperature minus 50 °C. Forcing may be applied if necessary. Cooling in still air shall be applied. Random hardness measurements shall be taken and the hardness shall not exceed 248 HV10.

For austenitic stainless steel, the maximum temperature during alignment corrections shall be 650 °C. Temperature-indicating crayons or contact thermometers shall be used to measure the maximum temperature. If temperature-indicating crayons are used, a margin of 50 °C shall be taken to allow for measurement inaccuracy, i.e., the reading with the crayon shall not exceed 600 °C. The duration of heating shall be kept as short as possible and no forcing shall be applied.

On Mon, Aug 9, 2010 at 7:12 AM, Shashank Vagal <nach_sam@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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