Thrust Blocks 5

[DGrayPPD]

Can somebody explain to me when thrust blocks are required on underground piping?

For example, I have a 6" fire water storage tank fill line where the piping drops underground after a control valve and comes back up before it ties into the storage tank. All BW piping. The civil engineer is saying that we will need thrust blocks because we've always put thrust blocks on underground piping. Is this correct?

What practices help dictate when thrust blocks are needed?

If more information is needed, please let me know. I have attached a picture of the line to give better visualization.

 

[MatthewJWillis]

This thread may be better served on the NFPA side.

Thrust blocks and their requirements are dictated in NFPA #24 as well as NFPA #13 Chapter 10.

R/
Matt

 

[DGrayPPD]

Thank you MatthewJWillis. Those codes may answer my question.

 

[LittleInch]

Even NFPA allows for welded pipe not to require thrust blocks - see e.g. NFPA 24 section 10.8.1.2

In the past much FW piping has been Ductile Iron push fit systems which need thrust blocks at bends to resist the end cap force.

One caution is whether the tank nozzle can withstand any loads on it - that support looks a way away and is only a support, not an anchor.

Otherwise you should find exemptions in the relevant NFPA codes.

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

 

[DGrayPPD]

Thanks LittleInch,

My knowledge seemed to end with the push fit systems. I understood needing them to prevent disconnection. But with butt welded piping I was a little lost. The support placement at the tank nozzle was dictated by the mechanical engineer after running stress on the piping.

 

[DGrayPPD]

In the event that they are used, are they required at every elbow?

 

[bimr]

No it is not correct.

If you are new to piping, start your career off on the right foot. That would mean that you will rarely if ever use thrust blocks. The reasons for not using thrust blocks are explained here:

https://daviddkent.wordpress.com/2013/01/22/thrust-restraint/

Because joints can be welded, steel pressure pipe usually does not require thrust blocks at special sections (valves, tees, elbows, reducers, etc.) However, thrust restraint is required in gasketed, pressure pipelines. The preferred thrust restraint will be mechanical restrained joints.

https://www.steeltank.com/Portals/0/pubs/Welded Steel Pipe 10.10.07.pdf

 

[DGrayPPD]

Thanks bimr,

That is what I always believed to be the case. I am not new to piping, however I have just not had to worry about thrust blocks often so when that situation arises, I like to get outside opinions. I will discuss this with my engineer that thrust blocks are not needed for welded piping.

 

[LittleInch]

Cppd - your question is not clear.

Bottom line is:

Push fit piping with no axial restraint on the joints - need anchor blocks every bend and tee.

Welded piping whether PE or steel of using mechanical joints which have avail restraint - don't need anchor blocks and if you have a temperature rise in your fluid will actually cause greater problems.

Unfortunately people who have only ever seen or worked predominantly with push fit systems believe you need anchor blocks everywhere..., but never know why only "we've always put thrust blocks on underground piping"...

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

 

[DGrayPPD]

Well, what do you do when they still tell you all underground piping requires thrust blocks regardless of whether it is welded or not

 

[DGrayPPD]

LittleInch,

I apologize if my question was unclear. It was basically just, are thrust blocks required for welded piping underground? It was my understanding that they are not required because the welded joints carry the thrust through the pipe but my civil engineer is telling me that all underground piping requires thrust blocks regardless of if it is welded or push fit, etc. When I asked why, I was told that all underground piping requires thrust blocks. When I told him welded piping does not, he stated that I was wrong.

 

[jgailla]

Your civil engineer doesn't know what he's talking about. Also, nobody uses thrust blocks anymore, they use restrained joints.

 

[LittleInch]

Depends on your reporting relationship with this idiot. If he is your direct boss then ask for an instruction in writing and get on with wasting the clients money. If not write a technical note quoting the relevant bits of nfpa regs showing you don't need to do it and send it to your superior and ask him or her to make a decision taking into account the misguided views of your civil colleague.

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

 

[DGrayPPD]

Thanks everyone for your thorough explanations.

 

[MJCronin]

I second the notion that the civil engineer is an idiot.....

Just to follow on the remarks above, yes many underground piping systems use restrained connections.

An example of one system is MEGALUG, offered by EBBA Iron Co. It has been in use on ductile iron pipe for many decades.

http://www.ebaa.com/products/dip/mechanical-joint-restraint

The elimination of thrust blocks enables many various types of savings including in UG piping layout, construction schedules etc.

MJCronin
Sr. Process Engineer

 

[rconner]

Just one comment, that I don't know whether or not relates to the present inquiry. A sort of pier-supported pipe stanchion (with the pier anchored or embedded at some depth), that looks like has an aboveground flat? cap support/tiedown for the actual line, appears some distance out from each tank. Near immediately off this pier, the line dips vertically downward.
The comment is this, if the soil mass and rigid risers/piping between the two piers (risers etc unsupported by anything but soil) were to settle as a unit downward relative to the two pier supports, it is possible quite high localized stress would result at the flat supports.

 

[DGrayPPD]

The vertical risers edges are 2'-0" and 2'-6" away from the edge of the concrete pier. The supports that you see are actually adjustable pipe cradle type supports. Those are requested per the client.

 

[KevinNZ]

I agree with Rconner. The riser next the pipe support is not the best design.

 

[bimr]

Also agree with rconner's comment on the sketch. Anchors are not normally placed at 90°offsets, and should be strategically located

 

[fel3]

jgailla…

"Also, nobody uses thrust blocks anymore, they use restrained joints." Well, the cool kids don't use thrust blocks anymore, that's for sure, Unfortunately, here in Central California, most engineers I know and many clients I have worked for insist on thrust blocks on their water mains. Years ago, one of my colleagues was even told by a client that restrained joints were fine, as long as they were backed up with thrust blocks.

Fred

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