PREHEAT of WELDED STRUCTURES

[ghan]

Hi
A plate was welded to a column by E6010(ASME standard of electrode) as root pass and E6013 (ASME standard of electrode)as filling passes. All materials are st37 and the thickness of base plate is 25 mm and it should be preheated about 70 C in conformance with ASME, but it wasn't preheated.
How can I test the column to determine whether we can use it in the structure or not?
I should add that the results of all N.D.T.s including U.T.,M.T.,V.T. are accepted but I can't reffer to them to judge about the soundness of the weld in this case, can I?
And what is the solution to overcome such a problem after welding?
I would appreciate any suggestion,
GHAN.

 

[Rjeffery]

Generally, Preheating is used to prevent 'stress' from being introduced into the weld and heat affected zone. If the NDT showed no defects (rejectable indications) then more than likely the weld is sound. If your structural engineer is still concerned, he may suggest post heat treatment to releive any 'stress' remaining in the weld.

Good luck.

 

[sayee1]

Preheat is essentially required to slow down the cooling rate. Slowing down the cooling rate sure reduces welding stresses, but mainly eliminates the formation of unsuitable microstructure(with associated higher hardness) in carbon steel welds and in addition provides sufficient time for the hydrogen in weld metal to escape. That is why many codes and standards base the preheat temperature as a function of the thickness of the materil to be welded, the CE of the metal, and the hydrogen level in the weld. Having used E6010 + E6013 consumables which are both the non hydrogen type, it can be expected to have higher hydrogen in weld metal. St37 has typically what levels of CE? I will have to check that out, but like Jeffry, I agree that PWHT is a remedial action as in addition to releiving stresses, it would let the hydrogen diffuse out of weld and reduce levels of hardness in HAZ . Thanks and regards
Sayee Prasad R
Ph: 0097143968906
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