ID No: 28518
Dear All,

Please solve my Clarifications.

1.Is the value of LCL (lower Confidence limit) same as Qualified stress ? Or Else, We have LCL value only. Then how do we calculate Qualified Stress. In ISO 14692, they mentioned the formula Qs= (P*D)/2*tr. But, In our CII Input, We have only place to put the Qs Value. (My Doubt is Diameter and thickness are varying in our Model.Already My friend has clarified that both are same, Please confirm.

2. Kindly clarify, what is the exact reason, Code stress value is higher in Sustained case (f2=0.67) than other two (f2=0.83)sustained with thermal,and (f2=0.89)Occasional loads. (ISO14692)

1. Yes LCL is same as Qs.Look at ISO14692-2, Para 6.2.3.1, equation 6, Pq=PLCL=f1*PLTHP.

2. Occa Allow= 1.33*Sustain allow.(0.67*1.33=0.89).

Thankx Mr.Nodal,

But, As per Iso 14692-2, Pq--refers qualified pressure not Qualified stress. Please correct me if i am wrong..

Pq=PLCL=f1*PLTHP (Long term hyd static pressure)
Qs= f1*PLTHS (Long term hoop strength)

Also, Qualified pressure = (Pq *D)/(2*tr) Then how to calculate Qs.Because In our system, Dia is varying.(branching etc). If not so, where we are using this formulae.Kindly reply.

2. If Occ allow = 1.33*Sus all. If it so, then why the code stress value is stingent when f2=0.67. And it is liberal (code stres value reduces) when f2=0.83.......pls explain

Can u give your personal id. I want to discuss more with u. Unfortunately this forum is not active sometime.

Also, I am having clarifications on FRP underground piping. Where to consider the stiffness value in the piping input. If not so, how CII considers. How the property varies with Above ground /Underground piping.

1.First of all, Qualified stress is not a function of diameter alone (D & tr varies for same series). It is determind by FRP vendor by testing result (Vendor get LTHS by test and then multiply it with f1). Qs will be the same for all size for single series of product.

2. It is a method dictated by code, for metal piping why we have different allow for SUS, OCC and EXP.

Consider the stiffness when pipe is U/G and no stiffness when pipe is A/G.

Thank u.


1.P lcl = f1* LTHP.....only. then how can we take this value for Qualified stress which is equal to f1*LTHS. Kindly clarify.

2.How to consider Stiffness value in U/G Piping. Where?

3. While modelling U/G piping, thrust block on Tee/Cross, Where to put the anchor exactly. Is it right, when we put the anchor exactly at the mid portion of the tee. Pls confirm.

4.Surge Analysis: For pumps, discharge of 200Mtrs water line to a open end tank. Do we need Surge analysis. Having only three bends. Pressure P16. How to know,whether we need Surge analysis or not. Pls calrify.

Thanks in advance.

1. As I told you earlier ask vendor to provide it.

You need a qualified stress engineer to solve your problems!!

Your vendor should provide you following things to complete the analysis per ISO 14692:

1.LTHS
2.Sa(2:1)
3.Sa(0:1)
4. r
5. E modulus (axial)
6.Poission ratio
7. Density of pipe
8.Expansion Coff.
9. Ratio of Shear mod/axial mod

You need CAESAR II version 5.3 to do analysis per ISO 14692.Once you have these info call CAESAR II help they will tell you how to make CAESAR II file per ISO 14692.

If you want to follow UKOOA, ask above data except Sa(2:1)
and Sa(0:1).

II) To determine surge analysis need you should study your system, (long big pipe with high pressure-need surge analysis)In your case just 200m open to atmos line so I think no need for surge analysis.