ASME B31.3displacement stress clarification
ASME B31.3displacement stress clarification
(OP)
I'm in the process of designing a new pipe line using ASME B31.3 and just want some clarification on the analysis of displacement strains/stresses. The code states the following should be achieved:
SE<SA Paragraph 302.3.5
And that SE is calculated as follows:
SE=(Sb^2+4St^2)^1/2 Paragraph 319.4.4
Are the values for Sb and St the same as what are used in the calculation for Longitudinal stresses and how are Thermal Stresses accounted for in the calculation for SE? It was my original intention to simply use Thermal Strain multiplied by Youngs Modulus to calculate stresses in a straight run of pipe?
I also appreciate that as the analysis begins I may determine that other sources of displacement may need to be considered.
Any clarification would be greatly appreciated.
Jimbo
SE<SA Paragraph 302.3.5
And that SE is calculated as follows:
SE=(Sb^2+4St^2)^1/2 Paragraph 319.4.4
Are the values for Sb and St the same as what are used in the calculation for Longitudinal stresses and how are Thermal Stresses accounted for in the calculation for SE? It was my original intention to simply use Thermal Strain multiplied by Youngs Modulus to calculate stresses in a straight run of pipe?
I also appreciate that as the analysis begins I may determine that other sources of displacement may need to be considered.
Any clarification would be greatly appreciated.
Jimbo
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com





RE: ASME B31.3displacement stress clarification
- Steve Perry
http://www.linkedin.com/in/stevenhperry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.
RE: ASME B31.3displacement stress clarification
RE: ASME B31.3displacement stress clarification
Biginch when I say pipeline I meant a pressure piping system.
Thanks for any further help.
Jimbo
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: ASME B31.3displacement stress clarification
Thermal displacements are the most common / most significant and should be considered when calculating S_b & S_t.
- Steve Perry
http://www.linkedin.com/in/stevenhperry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.
RE: ASME B31.3displacement stress clarification
But surely the fact that they are defined as two separate stresses there must be some differences.
So if I purely have a straight run of pipe fixed between two Anchors, for the S_L calculation I would exclude thermal effect and purely look at pressure and bending stresses.
Is it intended that I account for the thermal effects ( not considered in S_L) in calculating S_E, predominantly stresses due to restrained thermal expansion and possibly additional bending stresses due to temp changes. S_L can be subtracted from the displacement stress range (1.25(S_h+S_c)-S_L) while calculating S_A (equation 1b). because S_L has already been calculated previously and not considered in S_E. So in summary can I say that S_E are additional stresses above those calculated for S_L encountered as the temperature changes???
Jimbo
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: ASME B31.3displacement stress clarification
But... if you have a situation with high enough axial forces to create a stress problem, the loads on your anchors (pumps, vessels, etc) are probably more of a concern than the pipe stress.
For additional clarification:
S_L is the longitudinal stress only due to sustained loads, a/k/a "sustained stress." 302.3.5(c)
S_E is calculated from longitudinal stresses exclusive of the sustained stresses.
For a simple system at constant pressure and varying between ambient and a higher temperature with no anchor displacements, considering only the longitudinal stresses:
S_ambient = S_L
S_E = S_operating - S_ambient
- Steve Perry
http://www.linkedin.com/in/stevenhperry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.
RE: ASME B31.3displacement stress clarification
RE: ASME B31.3displacement stress clarification
My system will have some straight pipe runs fixed at each end that will encounter thermal expansion stresses. For example a 4m straight pipe, working from 20oC to 40oC and with an expansion coefficient of 13x10^-6 m/m K between fixed supports, I estimated a stress of approximately 218MPa.
I also have bends etc that will suffer from additional bending moments as thermal expansion takes place. I'm assuming that the thermal moments discussed refer to similar moments that are calculated in standard beam theory??
LSThill - yes thats the code I have.
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: ASME B31.3displacement stress clarification
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com