Page 17 - HIWT Spring 2013 World of Welding

hiwt@welding.org HOBART INSTITUTE OF WELDING TECHNOLOGY

pREHEATING OF pIpE

RESpONSE:
By Elmer Swank, Jr.
CWI/CWE The type and grade of pipe would determine the requirement
HIWT Instructor for preheating. When welding some of the higher strength
types and grades, preheating may be needed to slow the
cooling rate of the weld and the heat affected zone (HAZ). If
the weld area cools too quickly, the weld and the HAZ could
QUESTION: become brittle and crack.

I was reviewing a Other factors to be considered when determining the need for
weld procedure and preheat are:
found that it specified 1. Joint Restraint – The higher the joint restraint, the
preheat of pipe to greater the need for preheat.
approximately 225 2. Material Thickness – Thicker material normally
degrees F. The pipe needs more preheating.
has an approximate 3. The welding process and the choice of filler metal.
wall thickness of .500 4. Weather Conditions and Temperature – Cold or wet
inches. The welding weather conditions may make it necessary to preheat
will be done in moderate climate (60-80 degrees during the to eliminate moisture and slow the cooling rate.
day). I have never seen this required except to dry the pipe
early in the morning and after a rain. Is this normal now? When the specific material type is known and all the other
I retired a few years ago and am trying to find out if this is factors have been determined, the welding code or standard
something new in the industry. should be consulted for preheat requirements. Preheat
requirements must be listed in the welding procedure.

TM 1.800.946.2281
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