RE: [PipingDesign] GRE Stress Analysis by Vendor

From: <Dennis>
Date: Fri Jul 29 2005 - 04:34:00 EDT


I have been involved in extensive analysis of above ground GRE pipeline systems recently and can advise the following points:

   a.. GRE is an anisotropic material so behaves quite differently to steel. Its axial strength is around 50% of its hoop strength. I would advise against analysing it as steel with the properties adjusted.

   b.. Caesar II currently included the UKOOA rules for GRE design rather that the more recent ISO 14692 rules.

   c.. In my experience the vendors and manufacturers are usually not competent to carry out stress or dynamic analysis of the GRE piping.

   d.. Centron do have the tools do do an ISO 14692 analysis for design purposes but this does not replace the need for a Caesar II type analysis.

   e.. Be wary of the many older "design guide" rules for GRE which include suggestions that the loads between anchors might be low. My own calculations clearly confirm that this is not the case. Many of the design guides include some very poor advice.

   f.. ISO 14692 includes design for cyclic service such as vibration and short term loads such as surge.

   g.. I would not take the manufacturers rating of the pipe at face value. Do some calculations yourself using ISO 14692 so you better understand the behaviour of the GRE material.

Dennis Kirk-Burnnand B.E. (Mech)

   -----Original Message-----
   From: []On Behalf Of Sajit Viswan

   Sent: Friday, 29 July 2005 4:06 PM
   Subject: [PipingDesign] GRE Stress Analysis by Vendor

   Based on the wisdom of having the stress analysis    performed by the GRE vendor.

   On a certain job, it was specified that the vendor    perform not only the thermal analysis, but also the

   Surge and the dynamic analysis.

   The GRE system scope for the vendor was an ambient    temperature 16" water injection pump

   suction header and manifolds. There is a spool of CS    between the GRE piping and the pump suction.

   In order to perform the surge analysis, the vendor    needed a lot of data.

   It turned out that it would take a comparable amount    of effort to have all that data compiled, as much as    it

   would probably take to do the analysis itself.

   It was later decided to remove the requirements of the    surge and the dynamic analysis from

   the scope. The likely surge pressures that the system    will experience was concluded to be

   less than the rating of the GRE piping being    requisitioned. There was no vibration data

   available for the pump. Besides the GRE piping was not    directly connected to the pump.

   Eventually the vendor was to do only the thermal    analysis.

   The vendor did the analysis using the CAESAR software.    The modelling was the same as the CS

   pipe analysis except that the property values for the    GRE piping were used.

   Overall, It occured to me that it may take only less    effort to do this in-house.

   The thermal expansion coeffecient of GRE is about 1.8    times that of CS and the Modulus of

   elasticity is about 1/15 times that of CS. This    attribute of GRE allows 2 anchors in a

   straight line with only marginal restraint load    increase, in comparison to loads that would

   have resulted, were it a CS line.

   There was a note about the GRE stress analysis being    different from a CS some time back.

   Could not trace that email by subject.


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[Non-text portions of this message have been removed] Received on Fri Jul 29 04:34:00 2005

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