TIG torch heating stress improvement (THSI) for girth weld of pipe

Two parametric studies were conducted to clarify the key parameters which control the effects of THSI. One was a theoretical approach by modifying a simplified calculating method of weld residual stresses and revealed the following: (1) the heat input of THSI should be increased in proportion to the pipe size and (2) the pipe inner surface should be cooled enough to avoid film boiling. The other study was an experimental one showing the following : (1) the modified calculating method of weld residual stresses can predict the effect of THSI by fairly good accuracy, (2) forced convection is not necessary on a vertical pipe to prevent film boiling during THSI and (3) repetition of THSI does not have much effects on the residual stress obtained near the weld. (author)