Thrust block design for large pipeline

[LearnerN]

I'm considering a preliminary thrust block design for a large steel liquid-products pipeline (20-24"). I am familiar with the engineering principles behind the design of a thrust block (as well as having experience with soils and structural design), but the only thrust block design guide I've been able to find is the "Guide to the Design of Thrust Blocks for Buried Pressure Pipelines" from the CIRIA (Construction Industry Research and Information Association). The scope of this design guide is only for pipe up to 4" in diameter, up to 360 psi test pressure, and forces up to 225 lbf. In other situations with larger sizes and higher pressures, the design guide says the principles don't change but the design is said to "need a strong element of engineering judgment and should be carried out, or at least reviewed, by engineers with the appropriate experience in hydraulics and geotechnics."

In terms of a preliminary design, if the principles are the same for a larger line and since I have experience in soils and structural design, what else would probably need to be considered when designing a larger thrust block for a larger pipeline with higher pressure? Per the design guide scope, this design guide really doesn't cover a broad range of applications with such a small pipe size as the max pipe size consideration.

Are there any other published industry resources out there for designing a larger size thrust block?

 

[BigInch]

You could easily be dealing with forces around 1000 X your 225 lbf above, if not more.
It is far more economical to design your pipe connection for lower stress and flexibility, forgoing installing an anchor block at all. Big waste of time, construction resources and money. I've seen some really stupid designs with 4m x 10m wide x 4m deep anchor blocks, simply because some pipe stress engineer didn't have a clue to what they should have been doing, using flexibility to eliminate all that force.

Here's the stupid brute force method. Guaranteed to give you the largest anchor blocks possible,

http://agit.org.au/site.php?id=261

Smart method is to forget about installing the anchor and allow the pipe to move where it comes up out of the ground. Then accommodate that movement between that point and the connection to above ground pipe and equipment without overstresses. Tell your pipe stress engineer to get off his bum and design a more flexible pipeline connection.

 

[LearnerN]

BigInch, I definitely appreciate hearing your input and perspective. Could you elaborate a little more what you mean about designing your pipe connection for lower stress and flexibility? Thank you.

 

[BigInch]

Already edited my first post to include your suggestions.

 

[LittleInch]

LearnerN.

The issue is that the amount of movement required to reduce the load coming from a buried pipeline to almost negligible is actually very small. So long as the connecting pipe structure allows this to occur then you should be able to do away with your anchor block.

The issue is that piping stress engineer just don't want to bother modeling this strange buried thing and they find it easier to state install an anchor and they design away from them. The problem then just gets moved to the pipeline engineer.

I'm with BI on this - the majority of anchor blocks are not actually required in practice. Even with an anchor block there is still some movement / loads from the buried anchor block into the connecting pipework.

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

 

[BigInch]

Anchor blocks are usually constructed only because some pipe stress program won't work without one and the pipe slides off the edge of the earth. When I'm on the client side, I think we should backcharge the engineering companies for all the tons of useless concrete that was actually filled in those thousands of holes. When I'm on the contractor side, I thank them for making fools out of the design engineers and look forward to a good company Christmas Party.

 

[nackra]

Consider joint restraint for your 20"-24" pipeline size

Some poor soil conditions require "huge" thrustblocks and if someone in the future digs up the soils supporting the thrustblock (not shown on Record Drawings) then the pipe joint can blow apart.

 

[BigInch]

Hope you're kidding there nackra. Huge blocks in poor soils just make things worse. They usually cause bends, breaks and twisting dislocation of equally poorly placed isolation joints nearby, as they settle deeply into that soil.

 

[cvg]

suggest you design your thrust block like the one in the photo, Figure 1

https://www.google.com/url?sa=t&rct...jJE5gZw_mf98DzeSA&sig2=5swVkGHXtRZTeUKRdizAUg

 

[CarlB]

It would help if the OP would state the pipeline material.
I assume this is jointed pipe, not restrained, and a thrust block is necessary due to the thrust generated due to the angle change. Not thrust due to temperature changes, as this is usually insignificant in water pipelines.

The advice from the Inches appears directed to welded fuel/gas pipeline design.

 

[BigInch]

cvg That's an Aramco project. Precisely one of the kinds of blocks I was referring to. Aramco was famous in the contractor's world for decades as having the most unreasonable requirements for anchor blocks. Previously they were not allowing their anchor blocks to move at all. That study (article) is the beginning of their awakening. They are just now beginning to allow their anchors to move a little. They have a long way to go yet.

 

[cvg]

joints should be restrained as necessary, whether that be by welding, flanges, mechanical joints, megalugs, tie rods, anchor blocks, thrust blocks or any other suitable device, regardless of the fluid in the pipe or any sort of angle, valve or fitting. concrete anchors are the least desirable option in my opinion.

 

[bimr]

If you are as familiar with the design of thrust blocks, then you would be aware that knowledgeable engineers no longer routinely use thrust blocks.

Contractors rarely install thrust blocks correctly. The soils are never never tested. What is the point of designing something that will not be installed correctly?