Difference between BS7159 and UKOOA

Dear all ,

I have a question on the study code for FRP pipe . Between the BS7159 and UKOOA code , may i know which code is more conservative in the calculation? Can anyone advise the differences and the market possession of UKOOA ? e.g estimation of how many percent of engineers worldwide are using UKOOA as a study code for FRP pipe analysis by compare with BS7159 .

Many thanks in advance to anyone answered my question.

Regard
Glenn

We used to demonstrated both BS 7159 and UKOOA in our FRP/GRP pipe section of our C2 seminar. From that analytical perspective BS 7159 is more conservative. Now we illustrate ISO 14692. ISO 14692 is similar to UKOOA.

Dear Dave ,

Thank you to your advise but thoughout my study on the volume 24 december 1997 mechanical newsletter published by Coade, from my understanding it is implies that the calculation using UKOOA approach is more conversative . In order to purify the answer ,may i request your further clarification so that i could judge the conclusion with solid support.

Glenn,

I reviewed the article and it states that, compared to BS 7159, UKOOA imposes "more conservatism on the piping operating conditions". I am not familiar with the limits to operation imposed in UKOOA. You asked about conservatism in calculation. There are enough differences between these codes that it is difficult for me to drawn blanket conclusions. For example, we use Young's Modulus times design strain as the stress limit in BS 7159 and a mix of LTHS, f1, f2, r & pressure as the stress limit in UKOOA.
A general conclusion of which code is more conservative would best come from an engineer experienced in the complete application of both codes.

BS7159 and UKOOA can't be directly compared because of what Dave said above.
The determination of both material strength and maximum allowable stress in both codes is different. UKOOA (just as ISO14692) uses LTHS as basis for the allowable stress calculation. This LTHS value must be determined using ASTM-D2992. Some manufacturers have this value, some don't.
BS7159 handles allowable stress more freely. You can (more or less) determine the allowable yourself.
Personally I try to use UKOOA or ISO14692 if possible because both material properties investigation and allowable stress calculation is normalized using this calculation method. If no ASTM-D2992 (copied to ISO14692) values are available I use BS7159. Problem is then that there can be discussions about the allowables.

Dear Corne and Dave ,

Thank you to your efforts for the clarification , i believe your advise has been clear the doubts between my client and me . But before we end this topic , may i request to ask one last question about how was the market demand about UKOOA code in worldwide ? Do you have any ideas about how frequent that analyst use UKOOA as a study code for FRP pipe ? E.g for me , I am all the while(Majority of the project that i involved) applying UKOOA as the study code for FRP pipe .

I mainly saw 3 codes used: BS7159, UKOOA and ASME B31.3. Currently I see a lot of companies moving towards ISO14692, which is actually the first worldwide FRP piping code.
Please don't let me start on using B31.3 for FRP piping (it is possible according to B31.3, but please never do it) but some American companies like to stay with US codes somehow and don't want to use British codes.
Between BS7159 and UKOOA I've mainly seen UKOOA. But as explained above it also depends on the way the FRP manufacturer acquired the material properties.

Glenn,

The ISO 14692 approach in evaluating FRP pipe is similar to UKOOA. So in that light, since the ISO standard is a more recent document, I would assume that UKOOA achieved wider acceptance than BS7159.

Hi all,

Dave, as you said above, BS 7159 and UKOOA defines allowable stress with different methods. So, can I conclude that for a same FRP pipe, I have one allowable stress value for each standard, and probably these values may got a large difference comparing both of them?

Thanks in advance,

Miyamoto

(Sorry for ressurrect an old thread!)

The way I see it, BS7159 is based on allowed strain. This strain is multiplied be the appropraite modulus of elasticity (hoop or axial) to set an allowed stress and both directions are checked.
UKOOA checks both hoop and axial but the axial limit is based on the remaining bending stress given for a given amount of hoop and axial pressure stress.
So yes, I would assume the stress limits assigned to these codes are different.

Dave,

This information was very useful.

Thank you very much.

Dave,

I have another doubt. Where I can find in UKOOA the equation for code stress as described in Quick Reference Guide page 4-10?

CAESAR consider for calculation as code stress:

Tab(f2/r)+PDm/4t < f1f2LTHS/2.0

I didn't find this equation at UKOOA code.

Thanks in advance,

Miyamoto

UKOOA says:
Pdes .LE. f1 f2 f3 LTHP

Where:
Pdes = allowable design pressure
f1 = factor of safety for 97.5% lower confidence limit, usually 0.85
f2 = system factor of safety, usually 0.67
f3 = ratio of residual allowable, after mechanical loads
= 1 - (2 sab) / (r f1 LTHS)
sab = axial bending stress due to mechanical loads
r = sa(0:1) / sa(2:1)
sa(0:1) = long term axial tensile strength in absence of pressure load
sa(2:1) = long term axial tensile strength in under only pressure loading
LTHS = long term hydrostatic strength (hoop stress allowable)
LTHP = long term hydrostatic pressure allowable

This has been implemented in the CAESAR II pipe stress analysis software as:
Code Stress Code Allowable

sab (f2 /r) + PDm / (4t) .LE. (f1 f2 LTHS) / 2.0
Where:
P = design pressure
Dm = pipe mean diameter
t = pipe wall thickness

We give you a switch to remove f2 from the stress equation.

Dave,

Thanks for your explanation, but I didn't understand the code at CAESAR.


If Sx = Sap + Sab, and Sap = PDm / 4t.

So, Sx = PDm / (4t) + Sab

Being, Pdes .LE. f1 f2 f3 LTHP,

so, PDm / (4t) + Sab .LE. f1 f2 f3 LTHP

And now?! What's the transformation to do?

Can you detail the equations from UKOOA to CAESAR Code Stress?

Thanks again,

Miyamoto

Axial bending stress due to mechanical loads (sab) is part of f3. Isolate sab in that design pressure inequality and that's your allowable bending stress.

Dave,

Sorry, but I couldn't. Would you show me a step-by-step how to isolate Sab?

I tried, but I got big equations that make no sense. And was very hard to isolate in a simple equation.

Thanks,

Miyamoto

Pdes .LE. f1*f2*f3*LTHP

LTHP*D/2t = LTHS

so, PD/2t .LE. f1*f2*f3*LTHS

knowing what f3 equals, solve for Sab.

Dave,

Finally!!! You are the best!

I found my mistake.

Now I can explain for project manager the results!

THANK YOU VERY MUCH!