Explosive Plugging of Feed Water Heater Tubes

[bpv66]

Does anyone have experience with explosive plugging of feed water heater tubes (ASME Section VIII, Div 1)?

There are several company's that perform this type of repair, however they apparently do not follow the NBIC. It appears to be a very common repair being performed in utilities across the country.

In my opinion, this is a Code repair. Welding is being performed on a pressure retaining item and NBIC interpretation 95-35 states that plugging of tubes in boilers and pressure vessels shall be considered repairs. Further, the 2015 NBIC requires welded and mechanical plugging of tubes in fire-tube boilers be documented on an R-1 Form (I know not exactly the same thing but close).

Does anyone have thoughts or different opinions on this? I would appreciate any feed back. I want to make sure I am not missing anything.

Thanks!

 

[EdStainless]

A plugged tube in a FWH is not considered a weld on a pressure retaining item.
Yes, they are commonly done. There a few guys doing it, a couple of them are very good.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[bpv66]

Ed,

Do you have any Code justification for that opinion?

What makes a feed water heater any different than a boiler, as far as the NBIC is concerned?

I really don't care if it's a Code repair one way or the other, but I want to make sure it is being done correctly.

Thanks.

 

[bpv66]

I've attached the NBIC Interpretation below. It doesn't cover the type of welding, but it clearly states the NBIC applies to these type of repairs.

INTERPRETATION 95-35
Subject: R-200 Definition of Terms

Question 1: Is the welding in of a plug to seal tubes in a boiler or pressure vessel
considered a repair?

Reply 1: Yes.

Question 2: Does the NBIC apply to plugging tubes by welding plugs to tubes and/or
their joints to tube sheets of tubes that have leaked, tubes that have
corroded to an unacceptable thin wall thickness, and tubes required to be
removed from service for operating reasons in boilers and pressure
vessels?

Reply 2: Yes.

 

[metengr]

Explosive plugs are not installed using welds. We dealt with this in Part 3 of SC R&A.

 

[bpv66]

This is very confusing because some of the repair company's are advertising "explosive welding" of plugs to the ID of the tube hole.

Did any interpretations come from the NBIC committee discussion? I can't seem to find anything. I've asked a couple of Part 3 SC members and am waiting to hear back.

 

[metengr]

No, there were no interpretations submitted because the explosive plug joint is not produced by melting or heat as with common fusion welding processes.

 

[bpv66]

Metengr,

That's the feedback I'm getting from others in the industry. Trying to find something concrete in writing. It doesn't help that the repair company's are calling it "explosive welding" on their websites. Thanks for your help in this matter.

 

[metengr]

bpv66;
Welding in the NBIC is where melting occurs between base materials with or without filler metal. Beyond this, other types of welding are outside the scope of the NBIC.

 

[bpv66]

Metengr,

I'm not sure I agree with your last statement. The NBIC states that welding shall be performed in accordance with the Construction Code. UW-27(a)(2) of ASME Section VIII, Div. 1, defines explosive welding as "a solid state welding process wherein coalescence is produced by the application of pressure by means of an explosion."

So, explosive welding is addressed in Section VIII, in addition to Section IX, and is considered welding. I understand that these Codes only address explosive welding relating to tube-to-tubesheet welds, however, these are Construction Codes, not repair Codes. I refer back to NBIC Interpretation 95-35 which states that welding in of a plug to seal a boiler or pressure vessel is considered a repair.

I admit, that I am not familiar with explosive welding and can only go by what I read in the Code, and connect dots. Maybe explosive plugging is different than explosive welding of tube-to-tubesheet joints.

I believe this may get revisited at the Part 3 R&A SC in January. There are a number of Jurisdictions and a local utility already questioning this method and I think it needs to be addressed in the NBIC with an interpretation, at a minimum.

 

[metengr]

bpv66;
Well I Chair Part 3 so I guess it will be added to our Agenda. I may decide to work on this.