FRP/RTRP Pipe Stress Analysis

Garf,

Use CAESAR II from COADE Engineering. They are very experienced in this area of stress analysis and in the new version 5.20, due in September they will implement ISO 14692.

Chama

thxs for the reply,

I am using CAESAR II ver 4.30.

This is my first time on FRP pipes. This is what I have done so far;

I have entered the total thickness of the (liner+structure) as the thickness of the pipe

I have also included the "corrosion" as being seperate

I have also entered the "E(axial)" value based on "ABCO" values as being 1.035E7 Kpa

I have also entered the "SC" value as being (1/3)*of the Ultimate Tensile & compressive Strength(axial-bending)= 69000Kpa*.333=23000

Am I doing this correctly ???- please help

Are there any good references/books on the net

thx

Garf,

It is very common to have the FRP pipe manufacturer perform the stress analysis and this is usually included in the pipe specifications/requisition. We have designed pipe systems from 50mm to 4000mm and have always specified that the manufacturer perform the stress analysis. FRP pipe as opposed to steel pipe is manufacturer specific and requires the experience of the manufacturer to perform this analysis.

chama

Before you start doing the stress analysis, you'll have to know how the structural laminate for the pipe will be made - filament winding (if so, what wind angle), hand lay-up, etc.; you'll want to be very careful with thermal expansion. The method of manufacturing should match the application, and nowhere is that more important than in a chlor-alkali plant. One resin vs. another or one lamination method vs. another can mean several extra years of life for the chlorine side piping systems. In my opinion, these parameters should be specified by a materials engineer working for or on behalf of the owner, rather than by a fabricator. Further, it is very important that the pipe is manufactured and installed by highly qualified vendors. When I left the chemical process industry in '04 they were in short supply, and the market has gotten tighter since I left. You'll need a materials engineer who is knowledgeable in how to spec out the materials, the methods of joining, a lining material, if any (which will depend upon the type of design of the electrolysis cells).

Thank you for the info,

Yes, you are very right. I just received this info from the client;

Here is some more info, so that you may futhre help me.

1. 110 Mil (2.79 mm) corrosion barrier consisting of 0.01" (10 Mils) Nexus Veil reinforced resin rich inner surface and 0.1" of (100 Mils) interior equivalent to two plies of 1-1/2" oz/sq ft chopped strand mat outer surface to be resin gel coat containing UV absorbers.

Resin: Vinyl Ester Hetron 922, Derakane 411 or Atlac 580. Structural to be fw per ASTM D2296.

Cure: Benzoyl Peroxide/Dimethylailine, BPO/DMA.

This pipe system is used where heavy metals must be avoided.

Use of Cobalt Naphtenate is not acceptable.

When used in flammable service outer three layers and gel coat to have antimony trioxide or approved Alternate added as flame retardant. Flame retardant must not be used in the corrosion barrier.

I am not familiar with the "wind angle" please clarify ?

In stress analysis what should the thickness of the pipe should be?, i.e the total of the three layers or only the structural layer ?

What about the corrosion allowance ?, is the corrosion allowance the same as the structural layer and in this case=2.79 mm

Please help,

thx.

The wind angle is the angle which the continuous strands of reinforcement make relative to the axis of the pipe in a filament wound pipe. Off the top of my head I have a hazy recollection that 54 degrees is the most common wind angle for corrosion resistant filament wound pipe. The actual angle you buy or want to buy may vary, depending on how the pipe is specified. The text you quoted is not enough to fully spec out the piping unless I'm remembering D2296 incorrectly or it has changed in the last couple of years, and the manufacturer would have considerable latitude to produce pipe with a variety of properties axially and in the hoop direction. Start by reviewing D2296.

The corrosion barrier does not provide much strength or stiffness in a filament wound pipe; likewise, the exterior gel coat does not significantly impact the strength. As for quantifying the corrosion allowance, that requires more discretion and responsibility than I'm willing to accept on an internet discussion board. Based upon the specs you've put up there so far, I hope that this piping is for pure brine and not chlorine gas...

As "chama" says, when I have been involved in large piping projects in the past, I have specified that the FRP piping supplier provide the stress analysis. Quite often, they were responsible for providing the pipe supports as well.

The critical component of a successful fiberglass reinforced plastic application is the utilization of an industry driven fiberglass manufacturer. One who participates in all the industry associations, provides papers and is on the vanguard of research and development.

Additionally, this manufacturer should have in-house engineering capabilities, preferably a registered P.E. and include stress analysis, fea capabilities and ASME RTP-1 certification.

This is a very easy access industry, very low cost of entry, and you typically get what you pay for.