Pipe Leakage at the Anchor Block 1

[Inchtain]

Greetings,

I hope that you could help me with a recent issue that I have never encountered before:

We have a 10" underground crude oil pipeline that collects three oil wells and reaches an arrival manifold. Before it comes over the ground, at the manifold, it passes through two anchorage blocks (concrete) and I guess that it was a very old design job as the pipe portion that is inside the concrete has an encircled welded sleeve (12" pipe).

A leak of the pipe due to corrosion around the pipe sleeve just before the pipe enters the second anchor block.

What the reason, in your opinion, was behind such leaks at such locations? and do you think that welded plates are better than the welded bigger pipe for fixing the pipe in the anchor block?

Due to the criticality of the location (another 16" pipe that carries the production of 5 oil wells to the manifold is anchored with this pipe at a distance of only 0.5 m), what is the best solution here? to replace the pipe after demolishing the concrete with all the risks involved, by-passing the second anchor block, or replacing the last pipe section with an 8" pipe that can be easily inserted inside the leaking 10" pipe, which is, in turn, will act as the pipe sleeve?

The operating temperature is around 55 oC and the working pressure is 680 psi.

Thanks very much for your input.

 

[LittleInch]

Could do with a drawing here please.

Anchor blocks are notorious for leaks as you get higher stresses, bending moments, movement which destroy the coating and CP doesn't work.

Is the 10" line now shut down.

This is one more big reason I really don't like anchor blocks. Anything goes wrong and you can't fix it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Pipe should only be attached to anchor blocks using an Anchor Flange. If you use an anchor block. They should be avoided when pipe is not immediately attached to movement sensitive equipment.

https://stantonsales.net/pipeline-anchor-flanges

As LittleInch says, plan, profile, with dimensions, elevations and photos would help us give you some suggestions. Otherwise we probably won't be able to tell you much.

We will wait for your information.
Thank you.

 

[Inchtain]

Thanks very much.
I'll provide some details and photos when I am back on site

 

[Inchtain]

Hello again,

I thought I could provide a schematic diagram for the situation where I added some features to a photo from the web.

I hope that explains the case well.

I look forward to hearing your opinions.

Thanks

 

[1503-44]

Trying to reduce movement of pipe, which anchoring blocks do, ALWAYS increases pipe stress.

Anchor fittings distribute stress from pipe to block evenly. If those were not used there are extreme stress concentrations at the pipe to block interface.

What is more here are that there are 3 pipes. This is an impossible situation guaranteed to leak eventually. Each pipe should have an independent anchoring point.

Maybe there is also damage to the pipe coating and corrosion leakage. Stress can sometimes increase corrosion and corrosion ALWAYS increases stress.

 

[HTURKAK]

Inchtain,

Apparently, the sketch that you have posted obtained from internet and a second anchor block added with paint brush etc. So it does not reflect the situation which you have described in your thread..

As far as i understand,the pipeline is underground and when reaches to manifold site, it is above ground. So , there must be vertical bends ( one is underground and other above ground ). So the sketch does not reflect your case.

https://specialties.bayt.com/fr/spe...se-of-thrust-anchor-thrust-block-in-pipeline/

In order to get valuable comment, you can post some excerpts from the dwgs even a sketch ( showing the plan and profile with vertical bends, anchor block locations and sizes ) is better than any picture got from the web..

 

[LittleInch]

Inchtain,

Looking at your post here I think, think, you have a buried line with apparently two anchor blocks.

At an operating temp of 55 C I can only assume the first anchor block has moved due to be inadequate to resist the load and then they built a bigger one.

This is a dreadful design and will be imposing large stresses and bending moments on your pipe and you're probably lucky it has resulted in complete failure...

As for the best solution, I can't really give you good advice as I don't really understand what you have there, how critical one pipe is, whether the anchor blacks have in fact moved or if you need to pig all the lines or not ( an 8" inner pipe would stop you doing that) or any of the other dozen inputs and considerations or limitations you have.

But anchor blocks in general are bad news and really should be designed out, but many engineers are lazy and just stick them in because that what they used before without having any idea about what the loads are and how to resist it. Especially in sandy locations the anchor blocks might need to be the size of a small house to prevent movement of the pipe, most are just flimsy bits of concrete dumped in the desert and badly installed. So no easy solution. You can see everything, we can't, so it's your call.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Most anchor blocks are installed only because pipe stress programs don't work well without them and the stress engineer is too lazy to figure out a more flexible and low stress option.

 

[LittleInch]

The issue then is that it is very easy to specify an anchor block in a stress program with zero movement x,y,z and M, but rather more difficult to turn that into reality in the field....

The worst is when someone models a pipeline coming into a facility as a "free end" because "we don't know what's on the end of it" and then the piping designers blow a fuse because of these huge movements they need to accommodate. Only every now and then can I get the two stress engineers for piping and pipeline to create one model to actually design out those terrible blocks that actually result.

Now THIS is an anchor block.. That's a man by the way on top of it. Good old Saudi Aramco.

Anything less that that is worse than useless.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

2 men! Note the anchor flange inside. At least they are building a proper white elephant.

 

[LittleInch]

Well they're building a house for the white elephant....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Very good that one. Quite so.

 

[Inchtain]

Yes, that carries a lot of the truth.

Anyhow, I am providing more details and photos for the current problem of the 10" pipe.

Material: API 5L Gr. X 52
Fluid: Crude Oil
Working Pressure: 700 psi
Working Temperature: 115 F
Nominal Thickness: 12.7 mm
Failure: leak inside the annulus of the pipe casing (12" Pipe sleeve welded to the 10" pipe when enters the anchor block)
UT check around: Min. 8.4 mm
Pipe wrapping was deteriorated with moderated corrosion noticed
The top and middle of the second block was cracked.

1st photo: Pipe between the 2 anchor blocks
2nd photo: Leak location at the part entering the second block upstream.
3rd photo: Concrete Crack

 

[1503-44]

Could you please save that docx as a pdf.
Thanks

 

[LittleInch]

Done.

These "anchor" blocks are effectively useless. There's no way above ground anchors like that can actually withstand the forces without bending or falling over due to the moment forces applied to the foundations.

That second block should be jack hammered out and just repair the leak. It is probably leaking in part due to corrosion and part due to additional stress / bending moment because to the collapse of the second block.

It will be interesting to see if in fact that annular pipe actually has a flange or some other bits sticking out into the concrete. Be sure to send us some phots when you break it up....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Thanks.

 

[Inchtain]

Good morning LittleInch,

Thank you for the nice hints.

For sure, there is not any part sticking out to the concrete, as it is an old common design used at our site. It is the welded-on conduit pipe only.

But, I am still can not understand why a second anchor block was used for the pipes?!

And, we are still afraid that removing the second anchor block might affect the other 16" pipe that is anchored with the same block at a distance of less than 0.5 m?

Regards,

 

[LittleInch]

From the photos my guess is that it moved or cracked and hence someone decided to build another one.

Just break it up carefully and it won't affect the second pipe.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.