Dear Experts,

I am facing a problem in understanding the ASME B31.3 code requirement regarding the exclusion of impact testing for the LTCS material below -29 deg C to -104 deg C for which the code requires to satisfy the stress rato below 0.3.

Please give your expert advise for the understanding of the below three requirement with respect to caesar analysis.

According to ASME B31.3(FIG 323.2.2B), General notes ,
Stress ratio is defined as the maximum of the following
1) Nominal Pressure Stress (based on minimum pipe wall thickness less allowance) divided by S at the design minimum temperature.
2) for piping components with pressure ratings,the pressure for the condition under consideration divided by the pressure rating at the design minimum temperature.
3) combined longitudinal stress due to pressure,dead weight, and displacement strain (stress intensification factors are not included in this calculation ) divided by S at the design minimum temperature.In calculation longitudinal stress,the forces & moments in the piping system shall be calculated using nominal dimensions & the stress shall be calculated using section properties based on the nominal dimensions less corrosion ,erosion, & mechanical allowance

Thanks

Can anybody explain how the note no 1 & 3 is taken care in caesar analysis
.I mean what are the parameters that need to be changed to satisfy the above 1 & 3 points

Your urgent response would be appreciable

thanks

About the "parameters" you are looking for, you should be familiar with the relationship stress vs. thickness, for both cases i.e. "pressure, dead weight" and "displacement strain".
This is just the theory you must know.

About the requirement of calculation of that "combined longitudinal stress", the intention was to consider "the actual stress imposed at low temperature".

Maybe this point is better described in API 579-1:

Guidelines for stress calculations are as follows:

a. The circumferential stress should be calculated based on the nominal wall thickness minus the metal loss, future corrosion allowance, mechanical allowances, and the manufacturing mill tolerance.

b. The longitudinal stress should be calculated based on the combined stress resulting from pressure, dead weight, and displacement strain. In calculating the longitudinal stress, the forces and moments in the piping system should be determined using section properties based on the nominal dimensions adjusted for metal loss and future corrosion allowance, and the stress should be calculated using section properties based on the nominal dimensions minus the metal loss, future corrosion allowance, and mechanical allowances. Stress intensification factors associated with pipe bends, elbows, tees, etc., do not need to be included in the longitudinal stress calculation. The thermal stress does not have to consider a full design range, such as would result from a system with a high design temperature. It should best reflect the actual stress imposed at low temperature.

So I would understand that the last requirement is to evaluate an "operating longitudinal stress" calculated without any stress intensification factor.

I have also an advice. You seem to be focused to use Note 3 as independent statement; however please note that Note 3 belongs to Table 323.2.2, so you would carefully evaluate it through that table and the body text of B31.3

BTW, I'm not an enthusiastic supporter of Note 3. My doubts are based on what I cannot evaluate... See some details given in API 579: "Experience suggests that brittle fracture of piping is usually associated with unanticipated low temperature excursions" or "Vibrations in a portion of the piping system could initiate cracks that are cause for a high level of concern of brittle fracture. If the system could be subject to cyclic operating or impact load while it is operating below -29°C (-20°F), then an assessment should be made to determine whether the resulting cyclic stresses could result in the initiation and propagation of a crack.". I would add that both causes were involved in an accident that happened in my country.
And other questions: what about occasional stress due to seismic and/ or wind or other causes? Or maybe do you prefer to consider these events as "stress resulting from displacement strain"?

In the same time, for sure it is better to keep lower the stress but IMHO not as an substitute of impact test.

Best regards.