Hi all ,
How to model the concrete Encased pipe & how to include the stiffness of the concrete.

Pipe size is 2100mm & Concrete Encasement is 300mm.

Grade of concrete is M20(Quartzite) & Material of pipe is IS 2062.

Coefficient of thermal expansion for M20(Quartzite) : 0.000012 to 0.000013 /deg C

Coefficient of thermal expansion for IS 2062 : 0.000012 /deg C.

So should i assume no lateral movement between pipe & concrete .

It is a burried pipe which is from Condenser to the cooling tower.

Any suggestions for burried pipe analysis.

The only way to include the stiffness of the surrounding concrete would be to manually determine (compute) an equivalent modulus of elasticity.

Typically we recommend that any sort of cement/refractory be considered for "weight effects" only.

Mr Richard,

I want to consider insulation to be concrete , by changing the properties of insulation ,as i know the Modulus of elasticity of concrete . is it possible ?

Does the CII consider any lateral movement between insulation & pipe .

You can only have one set of material properties for stiffness across the cross-section. CAESAR II does not address composite cross-sections. If you really want to do this (and I urge extreme care here) you will have to compute equivalent properties and dimensions.



No. CAESAR II uses the "3D Beam Element", which you can think of as a thin piece of straw. So to CAESAR II, an 8 ft diameter pipe is the same as an 8 inch diameter pipe - they just have different (diameter) numbers which generate different stiffnesses. Things like insulation, refractory, and fluid are just additional properties that add weight.

Do a [Search] here on "beam element" and read the additional posts on this subject.

Mr Richard ,
Can i consider Concrete Encased pipe as Jacket pipe & give the stiffness of Concrete to Jacket .

The official COADE position is: "You can't count on the integrity of the concrete therefore we recommend that there be no adjustment in system stiffness due to the concrete."

This not reply , this also question:

While talking about the stress analysis of Cement lined steel , aren't we going to analysis which is similar to the analysis of GRP (FRP) lines , since the grp pipes and the steel cement pipes could be considered as composite pipes?? i think that the stress analysis of such pipes is not easy neither straight forward!!

Regards
Ahmad Akila
Piping design engineer
BCEC

There is a large section in the "Technical Reference Manual" on the analysis of FRP piping systems.

Both lined pipe and FRP pipe is more difficult to analyze then straight steel pipe. Never however try to check lined pipe (whether concrete lined steel pipes or PE/PP lined GRP pipe) in the same way as GRP pipe.

Why would you use concrete lined (internal) or concrete coated (external) pipe in a B31 Code application? In my experience, concrete lined pipe is used for seawater, untreated water, and the like. These primarily are not pressure applications, nor are they often subjected to thermal cycling.

Concrete coated pipe could conceivably be used for B31 applications, but the magnitude of the thermal cycles should be small. If I were in this situation, I would simply treat the pipe as a carbon steel system for internal pressure and thermal analysis, and deal with the external loadings via a hand analysis.

I'd also be very careful to make sure the concrete coating was not going to be damaged by the thermal cycles - I'm not sure what the coefficient of thermal expansion is for concrete but I'll bet it's small, and of course the concrete is relatively nonconductive to heat, so there will be thermal gradient stresses in the concrete also. Remember that concrete is really lousy in tension (thus the need for rebar), and once it cracks it has the potential to deteriorate rapidly.

Hi Naveen,

Read AWWA M11, this might help you regarding underground piping analysis.
Also, dont forget to search this forum.

Goodluck,