CEMP-E
TI 809-26
1 March 2000
e. Interpass Temperature. Interpass temperature is the temperature maintained during welding, until
completion of the weld joint. Minimum and maximum interpass temperatures are typically the same as
the minimum and maximum preheat temperatures, but may vary in specific WPSs.
(1) Thicker materials may absorb enough heat from the weld region that it is necessary to reapply
heat to the weld region prior to resuming welding of the joint.
(2) With maximum interpass temperature considerations, it may be necessary to pause welding
operations to allow the steel to cool to below the maximum interpass temperature before resuming
welding. Accelerated cooling using water should not be permitted, but the use of forced air is acceptable.
Cooling time may be necessary for larger multi-pass welds on thinner materials or smaller members.
(3) When necessary to shut down welding operations on a joint prior to joint completion, it should
be verified that adequate welding has been completed to sustain any currently applied or anticipated
loadings until completion of the joint. The joint may be allowed to cool below the prescribed interpass
temperature, but must be reheated to the required preheat / interpass temperature before resumption of
welding of the joint.
f. Postheat (PWHT). Postheating is the continued application of heat following completion of the weld
joint. It is not required by specification, but may be used in some cases when conditions of high restraint,
poor weldability steels, and poor hydrogen control exist. In most cases, when proper attention is applied
to preheat and interpass temperatures, and adequate control of hydrogen levels is maintained,
postheating is not necessary to avoid cold cracking. Under the difficult conditions mentioned, it may be
adequate to slow cooling rates through the use of insulating blankets applied immediately after
completion of welding. The PWHT described in AWS D1.1 Section 5.8, is for the purpose of stress relief,
not cracking control.
3. APPLICATION OF HEAT FOR STRAIGHTENING AND CAMBERING.
a. Principle. Heat applied from a heating torch may be used to straighten curved or distorted
members, and also to camber or curve members when desired. The method is commonly called "flame
shrinking", because the heat is applied to the part of the member that needs to become shorter.
b. Cambering Procedure. Cambering a beam with positive camber requires heat to be applied to the
bottom flange of the beam. It is recommended to first apply a V-heat to the web, starting with a point
near the top, to soften the web and minimize web crippling that may occur if only the flange is heated.
c. Maximum Temperatures. The temperature to which the steel may be heated as a part of the
straightening or cambering process is limited to 650oC (1200oF) for most structural steels, and to 590oC
(1100oF) for quenched and tempered steels. See AWS D1.1 Section 5.26.2. For TMCP steels, the
manufacturer's recommendations for maximum temperatures should be followed. It is recommended that
accelerated cooling using water mist not be used until the temperature of the steel has dropped below
approximately 300oC (600oF).
4. THERMAL CUTTING. Thermal cutting is used in steel fabrication to cut material to size and to
perform edge preparation for groove welding. Thermal cutting is generally grouped into two categories -
oxyfuel gas cutting, also commonly called flame cutting or burning, and plasma arc cutting.
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