ASNT Level III- Visual & Optical Testing
My Level III Self Study Notes Reading 4 Section 4B
My Level III Self Study Notes Reading 4 Section 4B
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6.3.8 Preheating before Welding<br />
Heating to the proper temperature before welding lessens<br />
the danger of crack formation and shrinkage stresses in many<br />
metals. Hard zones near the weld are reduced and lessen the<br />
possibility of distortion. Preheating also helps diffuse hydrogen<br />
from steel and helps reduce the likelihood of subsequent<br />
hydrogen inclusions.<br />
The need for preheating increases with the mass of the<br />
material being welded. It is most useful for the thick, heavy<br />
weldments used in bridge construction, shipbuilding, pipelines<br />
and pressure vessels. Preheating is also recommended<br />
for (1) welding done at or below – 18 °C (0 °F); (2) when the<br />
electrode is a small diameter; (3) when the joined pieces are<br />
of different masses; (4) when the joined pieces are of complex<br />
cross section; and (5) for welding of high carbon or manganese<br />
steels.<br />
Charlie Chong/ Fion Zhang
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