BRIS
Civil/Environmental
- Mar 12, 2003
- 525
Our specification requires design of a cross country steel water pipeline to AWWA, The designer is submitting designs to ASME B31.4. A standard which we are not familiar with in the water industry. Very helpful responses on the piping forum have warned of the dangers of mixing AWWA and ASME standards:
I would welcome any additional comments on the compatibility of the pipe stress design criteria proposed by the designer>
1) Hoop stress ASME B31.4 - 402.3.2 (a) -
Sa = 0.5*E*S
(Standard allows 0.72 ??)
2) Additive longitudinal stress 402,3.2 (d)
Sa = 0.72*0.75*S
3) Expansion stress 402.3.2 (c)
Sa = 0.72*S
4) Effective Stress 402.3.2 (e)
sa = 0.9 *S
5) Occasional stress
Sa = 0.8 * S
Sa = allowable stress
S = minimum yield strength.
Maximum surge allowance 10% 0f working pressure
Test pressure 1.25 * working pressure.
It would appear to me that the designer is reducing the hoop stress factor from the allowable 0.72 to 0.5 in order to comply with AWWA standard, but 1) is only allowing a 10% overstress for surge whereas AWWA would allow 50% and 2) is not reducing the allowable stress for other load conditions.
Am I getting a pipe that is substantially over designed in respect of working and transient pressures but under designed with respect to other loads and effective stress?
Do I need to buy myself a copy of B31.4?
I would welcome any additional comments on the compatibility of the pipe stress design criteria proposed by the designer>
1) Hoop stress ASME B31.4 - 402.3.2 (a) -
Sa = 0.5*E*S
(Standard allows 0.72 ??)
2) Additive longitudinal stress 402,3.2 (d)
Sa = 0.72*0.75*S
3) Expansion stress 402.3.2 (c)
Sa = 0.72*S
4) Effective Stress 402.3.2 (e)
sa = 0.9 *S
5) Occasional stress
Sa = 0.8 * S
Sa = allowable stress
S = minimum yield strength.
Maximum surge allowance 10% 0f working pressure
Test pressure 1.25 * working pressure.
It would appear to me that the designer is reducing the hoop stress factor from the allowable 0.72 to 0.5 in order to comply with AWWA standard, but 1) is only allowing a 10% overstress for surge whereas AWWA would allow 50% and 2) is not reducing the allowable stress for other load conditions.
Am I getting a pipe that is substantially over designed in respect of working and transient pressures but under designed with respect to other loads and effective stress?
Do I need to buy myself a copy of B31.4?