Post heating is a must--do activity as per your WPS requirements especially for Cr-Mo each time you wanted to stop your pre-heating machine. This practice helps to diffuse off any remaining hydrogen in the weld at present time, refine your grain size and to prevent fast cooling of your weld bead and HAZ.
PWHT is normally carried out after your weldment is completed and then subjected to NDT examination such as RT, UT, MT and/or PT and in certain cases, after repair of welds if there are defects that has to be removed as per the NDT requirements. PWHT is done only after all the visual and NDT requirement for the weld is satisfied. PWHT helps to further diffuse the remaining hydrogen, refine your grain size and toughens HAZ area.
I have worked with Cr-Mo (P12, P22, P91) materials before and based on my experience, my two cent worth for you is to do the post heating as per WPS requirement regardless whether you do PWHT sooner or later in order to prevent any unnecessary problems in the future
On Wed, Oct 6, 2010 at 1:12 AM, senthil raja <senthilrajabarathi@gmail.com> wrote:
Hi,
I m Senthil working in L&T. I m presently in MRPL project,
Mangalore. In our client(EIL) specification it is given that post
heating shall be carried out for the alloy steels (Cr-Mo) where PWHT
cannot be carried out immediately.
I need to know what is the time limit within which PWHT shall be
carried out without post heating. What is the standard or code which
can be reffered for this.
Kindly share your experience sirs & friends,
regards,
Senthil Raja.
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