Pipe Joint Allowable Deflection - standards

[BRIS]

This is another one of my problems resolving a dispute between the designer and contractor.

The designer has used nearly all of the available joint deflection at spigot and socket joints in his plan and profile design leaving only a +/- 2.5 mm tolerance for the contractor to work to in pipe installation. This is 1.6 m diameter PCCP (Pre cast concrete cylinder pressure pipe 16 bar). Not easy stuff to maneuver about the trench.

The designer claims his design is to industry standards and he has never come across a specification requirement to limit joint deflection to a percentage of manufacturers recommendation. The UK water engineering standards specification and BS 8010 covering pipe installation typically recommend that the pipe joint deflection, after installation, should not exceed 75% of the manufacturers recommended maximum joint deflection. And if there is a risk of settlement this should be reduced.

The designer doesn’t recognize UK standards! I am looking for other references in international standards, specifications etc. which specify maximum joint deflections as a percentage of manufacturer's recommended maximum that may be utilized in design and also limits not to be exceeded after installation.

 

[cr1973]

The owner/developer should step in and put the engineer in his place. Obviously this design engineer never gets out of the office.

 

[BRIS]

Thanks Cr1973 - unfortunately it doesn't work like that here (North Africa) it has to be in a code or standard. It doesn't matter if it falls down providing it complies with an international standard.

 

[GregLamberson]

BRIS

What is contained in the contract? That should be the governing codes for the project regardless if the design engineer is familiar with it, likes it, agrees with it or not.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[cr1973]

Is every single joint defelcted at the maximum allowable? A lot of times a single joint is designed to be defelcted, but the following 2 or 3 maintain the same slope. If this is the case, the defelction could be spread out between several joints instead of all on 1 joint.

 

[dicksewerrat]

The owner decides if this is accepatble. Are bends available for this product? Laying pipe with every joint offset would be tricky and slow.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[BRIS]

When I started in this industry (over 30 years ago) we rarely drew plan and profiles for water pipelines: just followed the ground profile with air valves at peaks and washouts at valleys.

Nowadays we appear to prepare plans and profiles for everything from 1" service connections to major trunk mains. Why? To keep the drafters employed?. (Ok often it is necessary to determine the design in the vertical to avoid other utilities and for record drawings - but I see miles and miles of Plan and Profile drawings for pipelines over virgin land) Most are drawn with straight gradients between valley and peak. I even see them with the pipe gradient annotated as a constant gradient along the length with all of the gradient change taken at single points at the trough and the peak. I have seen pipes 10 feet deep simply because the designer has designed the pipe as a straight line between two points rather than follow the natural ground profile. Why?

In this case I have posted above the designer has done just that. He has drawn the profile in straight lines with maximum joint deflections at troughs and peaks. He also has maximum horizontal joint deflection at the same point. His drafter clearly didn’t understand that you cannot pull 4 degrees vertically and 4 degrees horizontally at the same joint and still be within 4 degrees. The technical solution is easy simply smooth out the profile - pull 1/2 degree on each joint over 8 joints not 4 degree on one joint.

The problem is someone has to pay for revising the design and changing 300 mile of pipeline plan and profile drawings.

Dicksewerat - the contract has nothing other than a list of every relevant (and many irrelevant) international standard which allows the designer/contractor to cherry pick whatever best suits them. The scope of work describes methodology rather than the required end result/performance.

 

[rconner]

You have an interesting job. I’m not sure how such potentially quite complicated issues might be resolved without the input of the pipe manufacturer/designer of the specific joints involved. Some joint designs could conceivably have more security than others. I do know that at one time AWWA M9, Manual of Water Supply Practices Concrete Pipe, in the “Guide Specifications for …Installation of Concrete Pressure Pipe” chapter, contained the specific guidance in the purchasing section, “The pipe design details and layout schedule shall be prepared by the manufacturer for the contractor’s submittal to the purchaser…” and then subsequently in the installation section, “Minor deflections of the pipe alignment may be obtained at standard pipe joints; however, the maximum joint openings caused by such deflections shall not exceed the recommendations of the pipe manufacturer. When it becomes necessary to make larger deflections, sections of pipe with beveled ends or fabricated fittings shall be used. Random-length pipe and/or bevel adaptors may be used to make unforeseen changes in the field.” I think another chapter of this same manual talked about needs for/potential restraint of pressure pipe deflections. Beyond this, (along with other issues) I believe stab depths of even some large concrete pressure pipe joints can be quite shallow, and you are thus perhaps asking some sound questions.