I would like to draw the kind attention of Caesar II team to the fact that at present the displacement stress range is considered in the software according to Chapter II of ASME B31.3 only.

Chapter II has a limitation on the value of Sc and Sh (maximum 138 MPa only)while Chapter VIII has no such limitation. Hence the allowable stress according to Chapter VIII can be sufficiently larger than that according to Chapter II.

High pressure piping is very common in both process and drilling industry. Selecting 'B31.3' option in Caesar II doesn't reflect the proper code allowable and for such piping using the available option often leads to code compliance failure.

This topic was raised to Mr. David Diehl during CAU Express at Singapore on 28 July, 2016. I hope this feature will be properly addressed in 2017 edition of Caesar II.

Dear Tanvir

Thanks for good information. Can you please mention paragraph information where such limitations are mentioned !!

Hi Nitesh,

In page no. 17 of ASME B31.3-2014 (Chapter II), Sc and Sh is specified to have a maximum value of 138 MPa, which results in a maximum allowable displacement stress range of 206 MPa according to equation (1a).

On the other hand in page 122 (Chapter IX)of ASME B31.3-2014, there is no limitation specified on the value of Sc or Sh.

I would like to express my apology to refer to the wrong chapter no. for High Pressure Piping. It should be Chapter IX, not VIII.

Hi Tanvir.

Thanks for an information. It is really a good point.

But what I understand by reading which is " f is stress range factor,3 calculated by eq. (1c)4. In eqs. (1a) and (1b), Sc and Sh shall be limited to a maximum of 138 MPa (20 ksi) when using a
value of f > 1.0".

Its means that Sc & Sh should be limited to 20 ksi only in case when f >1.

Please correct me if my understanding is wrong.

Hi Nitesh

As per my understanding of the code I haven't found the relationship among the value of Sc, Sh and f. The value of f depends mainly on the number of load cycles whereas the values of Sc and Sh comes from material yield, tensile, creep rupture strength.

According to the code the value of Sc and Sh shall be limited to 138 MPa, irrespective of the value of f.

You can check this in Caesar II also. For experiment, you can take any material which has a higher Sc and Sh value than 138 MPa (such as ASTM A789 S31803) and then disable the 'liberal stress' option from the settings. With f=1 (default value)you will get a maximum allowable expansion stress value of 207 MPa only, not more than that.

Equation (1a)
SA = f(1.25Sc+Sh) = 1(1.25x138+.25x138)= 207 MPa

Hope this clarifies properly.

Hello Tanvir.

I have not analyzed any high pressure piping system(High pressure is considered herein to be pressure in excess of that allowed by the
ASME B16.5 Class 2500 rating for the specified design temperature and material group.).

However, to verify calculation of Expansion stress range, can you tell me the material group, design pressure and design temperature? I think that Caesar II should have a selection criterion to apply equation 1(a)/1(b) or 32 according to criterion if it is normal piping or high pressure piping in accordance with ASME B31.3.

Neeraj
"The harder I work, the luckier I become"

Yes, CAESAR II does not address the differences presented in the High Pressure chapter of B31.3.
High strength does not necessarily imply high FATIGUE strength. That's why, in 302.3.5(d), B31.3 limited Sc & Sh to 138 MPa a few years ago. I have just informally requested a review of the high pressure chapter in this regard.

Nitesh,

All materials are limited to 138MPa in (1a) & (1b).

As a separate issue: You cannot have f greater than 1.0 for "high strength steels" (ferrous materials, specified minimum tensile strength .LE. 517 MPa (75 ksi))

Hi Neeraj

Most of the drilling rigs' high pressure systems and relevant skids and manifolds (such as choke & kill, high pressure mud and cement, etc.) belong to this high pressure class (more than #2500). At present the design pressure rating and temperature can go as high as 20,000 psi and 149 deg C respectively for choke and kill manifolds. For the other systems design pressure can vary between 5,000 psi and 15,0000 psi and design temperature can go as high as 121 deg C.

ASTM A519 AISI4130 (stress relieved) is the most common piping material for the above application. The yield and tensile strength of this material are 85,000 psi and 105,000 psi respectively at room temperature.

So far I have seen two approaches in doing expansion stress for high pressure pipings.
1. Allowable stress is manually calculated and then compared with equation (1a) value. Lets say it is 250% higher. So a note is added manually in the report that stress value is considered within the allowable for a range up to 250%.
2. Some companies intentionally use older version of Caesar II which adopts 2008 version of ASME B31.3. In that revision there was no limitation of Sc and Sh value.

I hope the above addresses your query properly.

Hello Tanvir.

Thanks for your good explanation.

I fully understand your concern.