Hello Sachin,
See below the extract from ASME Sec-VIII,DIV-1 on the requirements of post forming heat treatments. Yes the code mandates only stress relieving as post forming heat treatment due to the fact that C.S /LAS can accommodate deformation strains, thus it's safe to perform post forming heat treatments well below the lower critical (AC1) temperature.
Unless forming is done above upper critical temperature (AC3) re-normalizing is not required. Some of the rationale as per my thoughts are as follows:-
- C.S and some LAS do not have appreciable changes in mechanical properties following forming below AC1 temperature under normal service environments.
- If the service media is such so as to cause environmental cracking such as SCC, then it would be dictated by process specific specifications such as NACE or appropriate API guidelines or specific requirements from process licensors.
- Normalizing causes changes of phases during heating and cooling. The resultant change of microstructure changes mechanical and other properties
- Normalizing is done in the mill under due care. Unless shops are well equipped, re-normalize following forming may destroy material properties.
- UCS-79 FORMING SHELL SECTIONS AND HEADS- Vessel shell sections, heads, and other pressure boundary parts of carbon and low alloy steel plates fabricated by cold forming shall be heat treated subsequently(see UCS-56) when the resulting extreme fiber elongation is more than 5% from the as-rolled condition. For P-No.1 Group Nos. 1 and 2 materials the extreme fiber elongation may be as great as 40% when none of the following conditions exist:
(1) The vessel will contain lethal substances either liquid or gaseous (see UW-2).
(2) The material is not exempt from impact testing by the rules of this Division or impact testing is required by the material specification.
(3) The thickness of the part before cold forming exceeds 5⁄8 in. (16 mm).
(4) The reduction by cold forming from the as-rolled thickness is more than 10% at any location where the extreme fiber elongation exceeds 5%.
(5) The temperature of the material during forming is in the range of 250°F to 900°F (120°C to 480°C).
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of sachin sankhe
Sent: Monday, August 16, 2010 11:22 AM
To: materials-welding@googlegroups.com
Subject: [MW:6522] Normalising requirment in code
Why ASME sec VIII div.1 is silent of heat treatment above lower transformation temp.I mean normalising is not mentioned any where.
As per ASME sec VIII div.1 if due to cold forming fibre elongation is more that 5% then it gives reference of UCS-56,where it mention only stress releiving.
In which code I can find Normalising requirment(Temp, Holding time,loading temp)
I am aware that temp of normalising is about 910 Deg.c & holding time is 1mm/min.But I need reference of code.
Regards
Sachin
 |
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding-unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
Comments