At present we are welding ASTM A333 Gr 6 pipes with TIG process, with flat consumable inserts, with inert gas backing for puging. The piping is nuclear grade piping to NB requirements for heavy water coolent systems at 88 bar prassure and 290deg.c.
PROBLEM:Dam placement, welding, radiography,PWHT, all are series operation, and unless particular weld joint in pipe line is cleard in all respects we can not take up next joint welding. Time cosuming operation and hence schedule delay.
There is a chace of dam getting lost in pipe line due to mistake and can cause blockage of coolent during initial operation.
IS IT REALLY NECESSARY TO GIVE GAS BACKING IN CARBON STEEL WELDING?.CAN IT BE DELETED SINCE IT WILL CAUSE MINOR OXIDATION
ON PIPE I.D. WHICH IS VERY NEGLIGIBLE COMPARED TO CORRISION
(RUST) THAT TAKES PLACE DURING PRECOMMISSIONING PERIOD.
we have qualified procedure and welders for non purge joints or widow purge joints. If there is no other technical reason we want to delete the purging requirement allowing minor oxidationinside pipe.
ANY COMMENTS FROM WELDING EXPERTS FOR NUCLEAR PIPING?
PDPRAO
Not an expert here, and have welded some nuclear in my younger days.
Why purge M-1, Group 1 material? This to me would be considered what is known as mild steel pipe with the 60/35 tensile/yield.
Don't know and not sure why the spec. calls out for purging of that material. I see how setting up for the weld, purging, clearing the dam, heat treat and then trying to shoot it, the entire process would then have to be repeated. I hope your bid included all the extra work involved. I hope there is an expert who will divulge information not known.
By the way, what is the dia. and wall thickness?
Purging the root pass in mild steel piping provides no significant benefit. The appearance of the root is obviously much better with the purge, and may slightly improve the ability to pass RT, but there is no other reason to purge it from the standpoint of material properties or weld quality. Subsection NB does not address when purging is or is not required, and it is not an essential variable for procedure qualification under Section IX. It is an essential variable for welder qualification, but you say that is already covered. It is up to the Owner to specify whether purging is required or not, so you'll have to discuss it with them or their design engineers.
As an alternative, you could use the dissolvable purge dam paper and flush the lines with water after installation is complete. You would need to have the purge inlet and exit through windows in the root pass.
Marty
Marty:
I thought about the toilet paper dams, but the process of purging would still be present. The concern of debris in the line prior to commisioning was also mentioned. I think this is the purpose of the post.
I too am at a loss over purging this material.
By pdprao
Date 03-10-2003 02:16
THANQ Mr MB SIMSFOR UR REPLY.
WE HAVE BEEN USING DISOLVABLE PURGE DAMS AT CLOSURE DAMS SOME TIMES AT STAILESS STEEL WELDS.BUT FOR CARBON STEELS AS YOU SUGGEST BETTER CLEANLINESS INSIDETHE PIPE MAY BE MAINTAINED WITH PURGING. THIS MAY NOT BE AN ESSNTIAL REQUIREMENT FOR MAINTENANCE WELD PROPERITIES. WHAT ADDITIONAL TESTS DO U SUGGEST TO DELETE THIS REQUIREMENT. THANQ ONCE AGAIN
PDPRAO,
You may want to check to nickel content in the A333, I seem to remember some years back welding A333 for cold gas service where the procedure required backside purging. Perhaps bacause of the impact testing requirements.
