Assessment life by cycle on FRP Pipeline - ASME B31.3 6

[drakkkko]

I'm in the process of checking a FRP (AWWA C950 Cl. 50 ) pipeline flexibility analysis by subcontractor. I asked why he uses Stress Range Factor (See Fig. 302.3.5) f=1 for reduction of stress allowance by cycle at ASME B31.3 and his argument it’s the following:

Subcontractor considered a complete thermal cycle to set N in equation f = 6.0*N^(?0.2) ? fm. The full cycle means, by subcontractor, is given for each plant shutdown. As the pipeline is under roof, the temperature range dominant it’s fluid range (T°min – T°max) so he did not consider important the daily temperature difference (T°min – T°max) of fluid to set it as thermal cycle (N). So his calculation is if the plant has an operating life of 26 years, considers 2 plant shutdowns per year then:
N = 2 * 26 = 52 cycles < 7000 ? f = 1.

My doubts is whether is it right, for FRP to set N = 52 or should he takes the daily temperature difference (T°min – T°max) of fluid to calculate N?

Temperatures data:

T° min= 50° F (Fluid Temperature)
T°max = 68° F (Fluid Temperature)
T°ambient = 5°/77° F

Any clarification would be greatly appreciated.

Drakkkko

 

[BigInch]

It would appear to be correct. You don't have thermal cycles unless the temperature goes up, then comes down, or v/v.

 

[Duwe6]

How often does ambient go below 50°F? If it is only during Shutdowns, that will probably only once per year, unless this is on the North Slope. It is just not that cold at both ends of any 6-month period, most locations. A 'true' temperature cycle is a fairly rapid swing of more than 10°/hr or 25°F/8-hrs.

Thus, I concurr with BigInch

 

[LSThill]

Reference Fluid cooling water FRP:

Requirement of the ISO 14692 CODE

Use FRP Flexibilites: such as BS7159 OR UK00A flexibility factor of 1.0.

Use FRP SIF:If checked and any code other than specifically addressing FRP BS7159 OR UK00A is in effect, all fitting will receive fixed SIF of 2.3

this reference is 26 pages.

Steve

 

[stanier]

BS 7159 is a withdrawn Code of Practice. It also has limitations on size and pressure rating. It could be used as a guide but not to be relied upon in any contractual matter.

ISO 14692 is a good reference that is current but cross referencing out of date documents is a problem.

Average wall temperature could be based on indoor temperature variation and fluid temperature variation. It is not going to be > ambient temperature but will be < than fluid temperature.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[LSThill]

stanier (Mechanical) Thank you!!

My reference was

COADE CAESAR II Seminar 2009 JOB: COOLH20 Fiberglass Cooling Water System Total: 26 pages

Steve

 

[T5580]

Using B31.3 code to analyze the flexibility of the FRP piping may not be the right one. The FRP piping design should be strictly followed the manufacturing guideline, simply because each FRP supplier has its own method of deriving the pipe properties. If this info is not available at time of performing the analysis, ISO 14692 is the one to be considered. In short, The flexibilities and stresses of the FRP piping system should be within the "design envelop" recommended in the ISO. Once the "design envelop" is met the analysis is done. Thermal fatique is not required per ISO 14692. This is only my 2-cents and hope it answers your questions. Good luck!

 

[stanier]

I did come across some work by Norska on the SIF valvues of FRP fittings. These fittings are commonly hand laid up, particularly for the larger sizes. The wall thickness is uncontrolled and thus the flexibility expected does not eventuate. It would appear the manufacturers think thicker is better.

One project I was involved in actually measured the strain at bends and then decided to reinforce the fittings, or not.

FRP is such a nightmare contractually for in plant product. You have to lock into a supplier so you can do the design. This leaves you exposed to cost blow out. You need to ascertain the prime cost of fittings beforehand. Estimate the quantum and cost the job. Then you can enter into an alliance type contract. Always insist on open book so you can see the actual costs.

Be wary of the negative pressure capability of FRP. FRP products do not always meet full vacuum criteria. If you have pump trips then your waterhammer analysis will tell you if column separation is going to occur and what your negative pressures are likely to be.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[drakkkko]

I would like to thank everyone which collaborated and helped me. The project wich I'm working for it's located in Chile North (Antofagasta city is a reference for location).

I have one last question specific to user Duwe6. You talked about a simple criteria to determinate a 'true' temperature cycle (more than 10°/hr or 25°F/8-hrs.), where that rule come from? for your own experience ? from ASTM / BS standar code ? I thinking to use that criteria but of course I need a documented support.

 

[Duwe6]

drakko, it was based on experience & eng. judgment. There is very, very little stress from a slow change in temperature -- all the pipe and its contents stay at the same temperature.
A rapid temp swing will give temp differentials in the piping in the contents, and may give a differential in the pipe from one area to another area. It is these temp differentials that cause extra stress. Your basic stress is the dead weight of the filled pipe, distributed over the pipe supports, and the internal pressure. Long before stress due to temperature changes needs to be considered, the local stress due to the pipe supports needs to be considered. You will find it greater by at least a factor of 10. The only substantial thermal stress I see is if some overzealous operator steams out the pipe. Please make it known to the operators that FRP cannot withstand steaming. Otherwise, the first time they try top recover from a freeze-up, they will destroy the system you are designing.

As stanier brought up, pump trips and the associated water hammer are also a substantial load, overshadowing temperature differentials.

 

[T5580]

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