installing buried chilled water pre insulated piping

[rajisha2002]

hi guys'
we are new at installing directly buried (in earth) chilled water district cooling piping .Our application is pre insulated black steel piping with welded joints.We had carried out stress analysis through a certified consultant ,software used was Ceasar-II .Result was cancellation of the design intent of thrust blocks & flexible joints on piping while introduction of concrete anchor points (mass concrete)at very few locations(at entry point of piping to buildings),further the piping was allowed to move with polystyrene wraps at changes in direction of pipes while remaining buried.
Is this feasible in normal practices?
The design consulant for the piping is very skeptical of the proposal and objected to the design of the concrete anchor blocks .
Please help ,if we have cerified concrete anchor block design procedures for buried steel piping.
Working Pressure in piping is very minimal 4.6 bar ,application is in the middle east area.Piping is buried with normal dune sand over it.

 

[pennpiper]

It has been a while since I did any work that required thrust blocks. However I do not ever remember using thrust blocks on steel pipe with welded construction. What are the thrust blocks there for? Are you thinking of putting them at the changes in direction?
Your commodity is chilled water. You did not say how chilled is chilled and you did not give any indication of the ambient temp. at installation so we are at a loss to help. As you and others know, as the pipe gets cold (or colder than it's installed temp.) it is going to shrink. The piping system will shrink away from your thrust blocks. So why have them?
Give us more data.

 

[chicopee]

You should always temper the results from computer program with common engineering sense. Thrust blocks may be needed if the change in pipe direction create high resultant in the piping. You may want to do some quick calculation where thrust blocks are proposed and make a judgement as to the effects of their magnitude. Same with contraction and expansion of piping, do some basic calculations and then calculate stress to determine the applicabgility of expansion joints. Never rely totally on computer programs for answers.

 

[stanier]

A fully welded pipe system does not need thrust blocks to withstand pressure. thrust blocks could be used in buried situtations to control the thermal movement.''The use of Caesar is problemmatical as this is a beam element program. Great for providing primary stresses but does not address the secondary stresses. In the hands of an experienced modeller who understands the swcience of buried pipeline design it may be of use. But it shold be combined with design of buckling, bending, shear and trosional stresses in local areas of high load. ie the htrust blocks.

Pre insulated steel pipe can be a problem if ground water is present. Differential movement of the ineer pipe compared to the insulation could break the vapour barrier. Once water enters the insulation pipe corrosion will quickly follow.

Modern materials such as Tyco's K Flo overcome this problem by providing an ABS pressure pipe, pre insulated with expanded foam and an outer ABS sheath. No amount of water will corrode the pipe.

http://www.tycoflowcontrol.com.au/t...ine_systems/Overview/plastic_products#ABSKFLO

This ABS pipe had been used in Australia and SE Asia for over thirty years. It is good to -40C and is extremely tough. It is used below and aboveground for pressure applications in all manner if industries. The lower modulus also helps reduce pressure transients compared to steel and GRP.