purging during c.s tig welding with flat welding insert 1

[pdprao]

Is it really necessary to give argon backing gas during welding ASTM 106 GR B PIPES WITH carbon steel welding insert using tig procss.The application is for nuclear piping. ANY ASME or AWS back up is there to delete this requirement. Any expert can can give his suggestion?

 

[Weldmedic]

AS far as I know, there is no specific ASME code requirement to purge carbon steel tig with insert. If you do, the root face will have a nicer appearance but from a mechanical standpoint purge will not make a difference.

With that out of the way, here we go, 3 points here...

1)Do you have a qualified Welding Procedure Specification that covers GTAW of insert without purge?
2)Are your welders qualified to weld an insert without purge?
Per ASME Section IX, If your welders qualified with a purge they must requalify to delete the purge. But, If they qualified without a purge they may use a purge.

3)Is this a customer requirement due to internal system cleanliness? If so, they may be pretty ridgid in regards to the purge. There will be some oxidation on the root of the weld. You would have to submit a request to delete the purge requirement. Not knowing your exact situation, are there more details you can cite as reasons to delete the application of the purge. Where did this requirement come from?
Write back with more info....

Steve

 

[pdprao]

Thanq Mr stev for ur reply. To clarify further about my thread regarding purging requirements for welding carbon steel pipe with consumable insret with tig process the following may be noted

1) we have qualified tig procedures without purging as well . The welders are also qualified for w/o purging. But these are mainly for closure weld joints where the dams cannot be placed. limited number of joints are done using this procedure.
2)As u said cleanliness is mainly a requirement for nuclear application which is the case here.
3)But the oxidation problemis due to welding is negligible compared to the overall buildup of corrossion products . This is because the system will be put in to service only after 3or 4 years after the joints are
welded.Atmospiric corrossion product build up is not prevented on i.d side of pipe. It is not feasible to protct as well due to continus construction work on pipe welding and and erection. Even it took 6to 8 years in these systems they are put in to service. Therefore i feel the damage due to minor oxidation is negligible.
4)The main problem being faced for carring purging is that
A)some purging dams are left by mitake in side pipes which have blocked the reactor coolent pipes.This is a costly mistake which has occured in more than 3or 4 times in different units. The reactor need to go for forced shud down and expose personnel to avoidable radition risk
B) Use of purging dams in a pipeline welding
a series operation in the sence , unless we complete a weld and clear ndt in all respects we canot take up next joint in a pipe line since the purging dam cannot be removed easily due to piping routing configuration.
4)Deletion of purging will accilarate the work, and minimise the risk of loss of dam in pipe line

5) we can adopt window purging in such joints where closure joints are to be welded
as we are practising now .
6) This riquirements of purging c.s welds was adopted from AECL Canda practice
7) If there are no mettlurgical implications
by eliminating fullscle purging,if we want
)delete this requirement where ever possible

8) cosidering these aspects and feed back we want decide to revise the specfication.
Hope to fet some more feed back on yhis sutable for PHWR coolent systems

 

[sayee1]

PDPRao
See comments against the points you made
1) You have qualified tig procedures without purging as well . The welders are also qualified for w/o purging.
2)Cleanliness is mainly a requirement for nuclear application which is the case here. So you are covered with WPS , PQR and WPQs.
3)The oxidation problems due to welding is negligible compared to the overall buildup of corrosion products . Atmospheric corrosion product build up is not prevented on i.d side of pipe. It is not feasible to protect as well due to continus construction work on pipe welding and and erection. I agree that the damage due to minor oxidation is negligible.
4)The main problem being faced for carrying purging is that
A)"some purging dams are left by mistake in side pipes which have blocked the reactor coolent pipes. This is a costly mistake which has occured in more than 3or 4 times in different units. The reactor need to go for forced shut down and expose personnel to avoidable radition risk " Are you not using water soluble dams? Isn't there any hydro tests after the welding of the spools?

4)"Deletion of purging will accelerate the work, and minimise the risk of loss of dam in pipe line" See response to 3A above.

5) we can adopt window purging in such joints where closure joints are to be welded as we are practising now.
6) This requirements of purging c.s welds was adopted from AECL Canda practice
7) "If there are no metallurgical implications
by eliminating fullsacle purging,we want to delete this requirement where ever possible. " Like Steve said there are no metallurgical implications, surely the properties of the welded joint for the PQR you have tested without the purging as against the properties of the welded joint for the PQR you have tested with purging should be showing exactly that!

Based on the above, I do feel that the purging can be done away with. In addition since you are talking of the effect of the purging on the welding times, maybe you can have a look at the purge bladders available from companies like Huttington, (I think Advani Oerlikon in India are agents for the same) to reduce the time and efforts for purging, if you have not already looked at this aspect. Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[Weldmedic]

Is this a plant currently under construction, or is this welding activity during a maintenance refuel outage on an existing plant? What size(diam and wall thickness) is the pipe being welded? Sayee brings a good point with water soluble dams.Intercon also markets purge dams.

SInce you have all the technical bases covered with regards to procedure and personnel qualifications you probably should go for permission to delete the purge.

I worked on PWR where the RCS piping was About 30" diameter with 3" wall Stainless Steel which also used insert with purge. We welded these joints by installing an ID track mount Diametrics Auto GTAW unit and made the root pass plus 2 layers on the ID. Purge was established in the weld groove by taping a plexiglass strip around the OD of the bevel, vented at the top. It allowed a close view of the insert being consumed as well as minimzed the time and costs for establishing purge. Once the ID was completed, an OD track was set up and 2 Auto GTAW units were used for weldout. Approximately 108 pounds of filler wire was welded into each joint, Xrayed every 1" thickness deposited plus Final PT ID/OD and a baseline UT.

Good luck,
Steve

 

[pdprao]

Hi Steve&sai
The problems of purging dams was on 12 inch, 8inch, 6inch 4inch dia lines and smaller dias. we noticed during intial operation. sbequently the problem was resloved .
we were using soluble dams also at many places particularly in stailess steels.As u
pointed out in your experience in PWRS , being stainless steel purging is essntial and need to comply. Being large DIA it is a better methoed u followed at ur PWR coolent circuit, which is not the case with us.
But i feel we must delete this purging requirement for carbon steels with TIG and cosumable insert welding. We can provid window purging which will minimise the oxidation to some extent . since i have to take a decision my self on this subject I had placed this problem to experts like u. Thanking u for ur valuble comments.

One point in this context is that GRINNEL who supplies these inserts has generally gives , during welding the root chemistry will under go changes due to evoporation of elements like mangan ,silicon,chromium etc at weld molten temp.This aspect is more relvant in s.s materials and alloy steels. and this aspectis taken care by insrt
chemistry also.

Summing up if we meet WPS,PQR requirements perticularly IMPACT prop we need not insist on full scale purging for ASTM 333 gr6
bace materials while TIG welding
pdprao

 

[pdprao]

Hi Steve&sai
The problems of purging dams was on 12 inch, 8inch, 6inch 4inch dia lines and smaller dias. we noticed during intial operation in few places. sbequently the problem was resloved .(fuel was not loaded)
we were using soluble dams also at many places particularly in stailess steels.As u
pointed out in your experience in PWRS , being stainless steel, purging is essntial and need to comply. Being large DIA it is a better methoed u followed at ur PWR coolent circuit, which is not the case with us.
But i feel we must delete this purging requirement for carbon steels with TIG and cosumable insert welding. We can provid window purging which will minimise the oxidation to some extent . since i have to take a decision my self on this subject I had placed this problem to experts like u. Thanking u for ur valuble comments.

One point in this context is that GRINNEL who supplies these inserts has generally gives , during welding the root chemistry will under go changes due to evoporation of elements like mangan ,silicon,chromium etc at weld molten temp.This aspect is more relvant in s.s materials and alloy steels. and this aspectis taken care by insrt
chemistry also.

Summing up , if we meet WPS,PQR requirements perticularly IMPACT prop we need not insist on full scale purging for ASTM 333 gr6
bace materials while TIG welding
pdprao