Internally Thinned Pipe 1

[Sharik]

On an ASME B31.3 General Service, piping system, the outside radius of a small bore, 2" NPS, pipe elbow has thinned due to localized internal erosion. As a temporary measure, is it acceptable to apply an external weld build up over the thinned area (lots of base metal thickness to weld to) with an electrode similar to the base metal and bring it up to the original nominal thickness? This would be to allow for continued plant operation until the next planned outage when the elbow would be replaced.

Thanks

 

[BigInch]

You're kidding, right?

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[BigInch]

I'd try one of these,

http://www.thomasnet.com/products/clamps-repair-pipe-14460802-1.html

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[Sharik]

I wish I was kidding. This was an actual request from a refinery in the US. They were so adamant they could just weld on the outside of the elbow, they had me doubting myself.

A clamp or other such 'coffin' is what I'll be recommending.

Thanks

 

[brimmer]

Wow, it is hard to believe things like this still happen, but when you have welders or ex-welders running maintenance or making decisions, what do you get, they know how to weld, so they weld...

 

[jte]

How 'bout slowing down the negativity here? Is there a technical reason any of you would not so much as consider an external weld buildup? Given sufficient base metal thickness for welding? Don't tell me you've never heard of a hot tap? Don't tell me you've never heard of a welded sleeve or encapsulation? And... Don't tell me you really believe a bolted box (aka clamp, coffin) offers superior reliability.

Sharik - If you're not comfortable with the concept, walk away from it and let someone else who has experience with welding on lines and equipment in service have the job. While the other guy is working, get a copy of ASME PCC-2

http://catalog.asme.org/Codes/PrintBook/PCC2_2008_Repair_Pressure.cfm

and read Article 2.2, External Weld Overlay to Repair Internal Thinning. From the Introduction of that article:

This article addresses the repair of pressure components (piping or pressure vessels) degraded by wall thinning due to... by overlay of weld metal on the exterior of the degraded pipe or pressure vessel section.

For what its worth, the last time I welded I was in 7th grade. No reason to lump me in with the bias noted in the post above.

jt

 

[MJCronin]

jte,

As I understand the original post, it seems that Sharik is interested in welding the pipe WHILE IT IS UNDER PRESSURE.

I believe that BigInch understood the situation in the same way.

Welded sleeves and encapsulation methods are established and proven.

Welding on a hot, pressurized system is a sure recipe for injury and death

My opinion only

 

[jte]

MJC-

I understand that the hot work is to be done on the run. It's done all the time. I would encourage you to revisit your thoughts regarding Welding on a hot, pressurized system is a sure recipe for injury and death. There are too many live people who, by your approach, should be dead.

I've engineered many repairs which were welded on the run. Some on rather "interesting" situations - some with very high temp (over 1000 F), some high pressure, some with rather lethal contents. All on the run. All performed safely.

jt

 

[BigInch]

I have no problem with a hot tap. I have a problem with a pipe "repair" attempted on an internal hole using an external weld. That wouldn't pass any pipeline construction repair criteria I know of. Hot tap? Sure, I'd rather make a 1 or 2" hot tap centered right on that internal hole, cut it out completely, withdraw the tap and blind flange it off. Then you'd have a nice new hot tap, not a buggered up repair.

Not saying it can't be done, just not within my sight. Extreme emergencies... maybe, but not for continued operation for months more on end until it becomes convenient to do a shutdown.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[MJCronin]

jte,

Hot taps and pipe encapsulation proceedures have been performed for many, many years in accordance with API and well-established company standards.

External welding on low pressure liquid systems is, of course, much less exciting than the same repair on high pressure systems. Death is not ensured by jumping from the back of a pickup truck, but a ten storied building is another matter.

What proceedures does your company use for external welding on hot, highly pressurized, operating systems ?

Any restrictions on temperature or pressure maximums ?

-MJC

 

[jte]

BigInch
External weld buildup for internal thinning, while not common, is not new. If the stress calculations pan out, why not do it? This type of repair is not intended to meet new construction criteria, but an argument could be made that conceptually it meets ASME VIII-1 through U-2(g) and ASME VIII-2 Part 5. If so, and B31 throws a user to Section VIII when something with geometry beyond its guidance shows up, then arguably this could be compliant with B31 codes as well.

However, that's not the point. The point is that this is a temporary repair to get to the next shutdown. It is not intended to fully comply with new construction codes. A welded pipe sleeve does not meet B31.3 (without, perhaps help from VIII). That does not mean that a sleeve is inherently dangerous. The arguments made against this are the same as those made against the very concept of Fitness For Service evaluations. Remind me again when B31G was first issued?

Would you believe that I'm familiar with a repair in which an externally corroded pressure vessel was repaired with internal weld buildup? It made sense when looking at the big picture. [No, this job was not performed on operating equipment...]

MJC

I like your pickup truck vs building analogy. But then, given one of my hobbies, I might point out that I would likely feel more comfortable jumping from a 10 story building than from a pickup truck: If said truck is going down a highway at 80 mph, I'd prefer to not jump. If I had some instruction in BASE jumping and good equipment, I'd choose jumping from the 10 story building over jumping out of the truck.

The point is that every situation is different, and we can make up a situation where a seemingly benign situation is deadly, just as a situation which is too hazardous at first glance can be dealt with in a safe manner with proper mitigation measures in place. Four killed in doing what was considered to be relatively safe (if there is such a thing) work:

http://www.csb.gov/assets/document/Tosco_Digest.pdf

To answer your question: No. By the time my group gets a phone call, there is a reasonable possibility that the plant P/T limits for hot work on equipment in service are exceeded. We'll get welding, materials, and mechanical engineers together and assess the particular situation and make a recommendation as to whether the plant should shut down the equipment to perform the repair, or if we feel that it can be done safely we'll provide specifics on how to do it. In some cases the weld procedure is detailed down to individual bead placement. Yes, there are plenty of cases in which a "shut down" recommendation has been issued.

jt