GRP products being proprietary the choice of component sizes, fittings and material types are limited depending on the supplier. Potential GRP vendors need to be identified early in design stage to determine possible limitations of component availability. The mechanical properties and design parameters varies from vendor to vendor. So it is utmost important that before you proceed for stress analysis of such systems you must finalize the GRP/FRP/GRE vendor. Several parameters (Fig. 1) for stress analysis have to be taken from vendor.
Stress analysis of GRP piping system is governed by ISO 14692 part 3. The GRP material being orthotropic the stress values in axial as well as hoop direction need to be considered during analysis. The following article will provide a guideline for stress analysis of GRP piping system in a very simple format.
Before you open the input spreadsheet of Caesar II communicate with the vendor through mail and collect the following parameters as listed in Fig.1.
The values shown in the above figure is for example only. Actual values will differ from vendor to vendor. The above parameters are shown for a 6” pipe.
Inputs Required for Analysis:
For performing the stress analysis of a GRP piping system following inputs are required:
- GRP pipe parameters as shown in Fig. 1.
- Pipe routing plan in form of isometrics or piping GA.
- Analysis parameters like design temperature, operating temperature, design pressure, fluid density, hydro test pressure, pipe diameter and thickness etc.
Modelling in Caesar II:
Once all inputs as mentioned above are ready with you open the Caesar II spreadsheet. By default Caesar will show B 31.3 as governing code. Now refer to Fig. 2 and change the parameters as mentioned below:
- Change the default code to ISO 14692.
- Change the material to FRP (Caesar Database Material Number 20) as shown in Fig. 2. It will fill few parameters from Caesar database. Update those parameters from vendor information.
- Enter pipe OD and thickness from vendor information.
- Keep corrosion allowance as 0.
- Input T1, T2, P1, HP and fluid density from line list.
- Update pipe density from vendor information sheet, if vendor does not provide density of pipe then you can keep this value unchanged.
- On the right side below the code, enter the failure envelop data received from vendor.
- Enter thermal factor=0.85 if pipe is carrying liquid, enter 0.8 if the pipe carries gas.
- After you have mentioned all the highlighted fields proceed modelling by providing dimensions from the isometric/piping GA drawing. Add supports at proper location from isometric drawing.
- Now click on environment button and then on special execution parameter. It will open the window as mentioned in figure 3.
Now Refer Fig. 3 and change the highlighted parts from available data.
- Enter the GRP/FRP co-efficient of thermal expansion received from vendor
- Calculate the ratio of Shear Modulus and Axial modulus and input in the location.
- In FRP laminate keep the default value if data is not available.
- After the above changes click on ok button.
- While modelling remember to change the OD and thickness of elbows/bends.