Revision of some salient point of Buried pipe stress analysis

Revision of some salient point of Buried pipe stress analysis

   Figure.1 Basic model

1) Soil Property based on CAESAR II Basic Model

[ultimatetables 1 /]

2) Caesar modelling

Figure.2 Buried model

1. a) Valve Pit. At the entry and exit of valve pit there will be sealing to prevent ingress of water inside of pit. As we can’t hold the pipe at these location due to

(i) Thermal expansion and

(ii) Layout limitation reason etc.

So if there is such situation then you must ask for suitable sealing and which can absorb the some lateral movement. Initially we can limit this lateral movement by 3 mm (by providing virtual guides with 3 mm gap) but this final value should be comeout of both stress engineer and vendor.

1. b) Temperature. Normally design temperature design temperatures of buried portion and above ground are different so we should take care of that. If no such values are available then we must compare the design temperature (Td)) with solar radiation temperature (Ts). If value of Ts> Td then instead of Td we should put the Ts in calculation input file at above ground portion of pipe.
2. c) Nozzle offset. If buried pipe coming out from ground near to the equipment nozzle then always should be remember that pipe routing should not be in line to the equipment nozzle projection. There should be some offset (as shown in figure-2). The offset length depends on the analysis requirement.
3. d) Virtual anchor. Stress system can be isolated from virtual anchor. If our stress system is not pipe line but connect to pipe line then in that case only we have to consideration pipeline portion upto virtual anchor. To locate the virtual need to model pipe line portion with some extra length and then check the distance while run the soil model (as shown in the figure-3).

Figure.3 Virtual anchor location

Reference: Intergraph Caesar II ver: 7.00.01.1600