Dear Shashank,
Hot adjustment of a weldment depends upon many factors like type of weldment, degree of distortion, material of construction and application of weldment as to which environment it has to be exposed. Normally, for pressure piping, welding distortion is not allowed to be removed by applying heat with flame and then to quench. All such distortions are recommended to be removed by cutting the weld and then to re-do.
But yes to cater the piping misalignment during fit-up before welding, hot adjustments are made with uniform heating in a temperature range of 500 deg C to 700 deg C for carbon steels and then cooling is done is normal air. There also exists criteria for low alloy steels and this practice is usually prohibited for austenitic stainless steels as it impairs the chemical and mechanical properties.
The best way forward for you is to consider the factors as mentioned above and if you decide going for hot adjustment to cover the degree of distortion, then you must carry out post heat treatment (if applicable) and then to examine the whole area with RT and UT examination.
Regards,
Ashfaq
thepetrostreet.com
On Mon, 9 Aug 2010 07:12:56 +0530 (IST), 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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