Dear Mr Asghari,
What is the lowest design temperature for the tanks ?
Usually the procurement specification for steels should indicate the impact test requirement, that is at the design temperature. One may ask for impact at lower temperature (i.e for minus 500C design one may specify minus-550C in the specification), however impact values can be erratic, because the ductile to brittle transition for a specific steel at some temperatures can be drastic. I have access to API-620 but not to BS-7777, hence I could not verify the LOWERMOST DESIGN temperature requirements for this steel as per BS -7777.
However based on the information supplied below on the basis of the attached data sheet it looks to me that the lowest guaranteed impact temperature for this steel as per EN-10028-2/3 is -500C (minus 50 deg C) for guaranteed 42J lateral and 27 J transverse impact energy as supplied by various mills.
Requirements for impact energy on weld and HAZ at the impact test temperature should also be specified by the design code. Usually the impact values after welding + PWHT(if applicable) should be less than that specified for base metal (to take into account , the effects of thermal cycles.)
As a thumb rule if one gets the impact values in the base metal (during procurement), which is 2-3 times more than the values after fabrication, then there should not be much concern.
Feel free to ask me if you have any concern, if I have a copy of BS-7777, I may clarify your query fully.
Machine Dynamics & Component Integrity Dept.
Engineering & Training Services Division
ONTARIO POWER GENERATION Inc.
PO Box-2000, RR-55(South)
Tel:-(519) 587-2201, Ext 3107--in Nanticoke
(416) 231-4111, Ext 5925--in Kipling,Toronto
Fax: (519) 587-6814
From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of ali asghari
Sent: Sunday, January 10, 2010 11:57 PM
Subject: [Norton AntiSpam] [MW:4009] material procurement for liquid gas storage tank
I have a question about procurement & preparation of material specification that related to construction of storage tank for cryogenic liquid gas according, API620 & BS7777. The specified steel for this project is P355NL2,THAT according BS7777-PART2 the impact testing is carried out in -50-(delta T).(delta T is acquired according ANNEX A) now manufacture of steel said that due to time consuming of producing (delta T),he tested in lower temperature of -50, for preparing of order & material specification , what additional requirement or testing is given to ensure haz &base metal have adequate impact value?