Weld Caps on Tee's, In place of Elbows. Normal Practice? Reasons? 3

[Cuemaster64]

Good Day Everyone,

My conundrum is whether to disregard this situation or to bring it to someones attention.

1) I do not like this situation for my Hydro purposes due to the fact that I will never get the air out of this pipe.
2) Process that this pipe is being used on is for Bitumen, and I believe that flow around this corner will create extra agitation that, if memory serves, can help create H2S gases.
3) Can I be enlightened as to why this would be a good practice, if there is one.
4) If the cap at the top of the drawing was to be turned so that the tee runs parallel with the run (like the one at the bottom of the riser) would it achieve the same purpose?
5) As a side note this occurs on more than 1 drawing - multiple instances.
6) This work has not been awarded but do you think it possible that they (Engineering Firm) will catch this and rectify it with new drawings.
7) I guess all in all is this acceptable?

Just a topic that has me a little perplexed right now, so I thought I would ask the experts.

http://files.engineering.com/getfil...dfc-9aa3-d1dbb1d44bbc&file=Weld_Cap_Issue.png

 

[Gator]

Target tees:

http://www.eng-tips.com/viewthread.cfm?qid=60189

Piping Design Central

 

[austsa]

It suggests to me that the design plan is for the individual spools to be hydrotested in the shop, then caps will be cut off on site and welded to other spools.

 

[Gator]

Generally there'd be a pup piece (exactly 6" long!) and scribe line before the cap if this was for that purpose. Not to mention a note on the iso: "Cont. on dwg..."

Piping Design Central

 

[zdas04]

I would put a tee in that position, but with a blind and a vent on it. As a target tee, the blind has considerable extra mass that a weld cap wouldn't have.

In terms of your list:
1. The volume is too small for enough air to accumulate and cause a problem.
2. The void will not cause extra turbulence nor increase the amount of H2S
3. As a vent/future point is is a very good practice. With a weld cap it simply removes a high-risk erosion point
4. No it wouldn't, it would force the fluid to make the turn in steel and there would be no erosion benefit.
5. OK, means it probably wasn't an accident.
6. Since it apparently wasn't an accident, it probably won't be "fixed" unless you throw a fit.
7. Sure.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[europipe]

In my opinion ,it has nothing to do with venting,
I saw it more with decoke lines, the construction is created because elbows would worn out very quickly. The tees would silt up and you have a protection against that.

 

[LittleInch]

I'll add a little here of my own experience to add to those posts above.

To start with your initial headline questions

Normal - No, that's why elbows are used, but for when you should, see below

Reasons - Normally restricted to two or three phase gas systems with particles (gas wells normally). The theory is that the particles can't change direction as fast as the gas and either hit the end cap or flange and also slow down as they enter a dead end. Also used for high velocity liquids (> 4-5 m/sec) and liquids with hard particels in (sand grit etc). API 14E is a common calculation to see if erosion is likely. Unless one of these apply and I can't see bitumen doing so, then it is simply a waste of money as one tee and one cap plus an extra weld, costs more than a single LR elbow. You would need to ask why they (the designers) thought that a normal elbow would erode before the end of design life.

The other reasons alluded to before is where the design allows for "future" connections at these locations then it makes it easier to have one weld instead of two.

The downside is that you can get "gunge" build up of dirt etc in the dead end and hence makes it very difficult to clean out the pipe work. That's why there is normally a flange and blind so that if cleanliness becomes an issue or there is a blockage, you can get access to the pipe very easily to clean or remove the blockage. Here you would need to cut the cap off.

We are all assuming by the way that flow in your iso is from bottom right to top left. If it's going the other way then this design is incorrect.

Your points,
1) It's not great but the volume should overall not be significant. It could be that you can orientate the spool to avoid this as the high point.
2) Flow through a tee in this direction has a higher pressure drop than an LR elbow, but shouldn't be sufficient to cause undue cavitation.
3) See "reasons" above
4) NO as the fluid would be impacting on the top of the T and if it is erosive, would very quickly erode the inside of the tee
5) Common reason or maybe just common piping designer....
6) Maybe if they are on a price, but all depends WHY someone has done it this way. Unless the root cause is understood, challenged and overturned then it won't.
7) It's acceptable, but not lowest cost.

Let us know what you find out.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Cuemaster64]

Thank you all for your experience and knowledge on this matter.

As it goes, "I learned something new today" and that is a good thing.

Did not know the term "Target Tee" and will place it in the memory banks. Possibly even do a little more research as well.

Thank you all again.

Cheers

 

[Gator]

Thanks for getting back.

Is there some study of the percentage of Eng-Tips askers' follow through (i.e., resolution of problem)? It's always nice to find out what the outcome is when people offer help.

Piping Design Central

 

[pennpiper]

The key to this is the line "2) Process that this pipe is being used on is for Bitumen" in the original post.
Therefore, in my opinion europipe has got the correct answer.

Sometimes its possible to do all the right things and still get bad results

 

[LittleInch]

Is bitumen that erosive? If the fluid is particle free then why is it a big issue for elbows?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[weldstan]

Bull head tees are often specified where abrasion/wear is part of the service - flow is into the head/cap.

 

[Cuemaster64]

To LittleInch, and others who might like some light reading.

This site might help explain the amount of solids in bitumen.

http://www.thecanadianencyclopedia.ca/en/article/bitumen/

This may not be the most technical of pages but might give you the gist of what we face up here in the "Great White North"..

Regards,

 

[Gator]

The piping could have been specified "for bitumen service" and used for gritty bitumen/produced water from the well. Further downstream is desanding.

Piping Design Central

 

[LittleInch]

That's fair enough - it's what I would call "raw" bitumen as opposed to the stuff coming out of a refinery for use on the roads. If there is a good reason, then bull head or target tees are justified, if there isn't they're not.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way