Thick wall / high pressure pipe wall thickness calculations

[mariolucas75]

Dear All,

For pipe thickness calculations:

API 574 says for metallic pipe for which t ≥ D/6 or P/SE > 0.385 requires special consideration.
What is this special consideration? Where shall i find it ?

ASME 31.3 Para 304 Straight pipe under internal pressure says:
For t ≥ D/6 or for P/SE > 0.385, calculation of pressure design thickness for straight pipe requires special consideration of factors such as theory of failure, effects of fatigue, and thermal stress.

So, ultimately where is this formula available for thick wall / higher pressure (t ≥ D/6 or for P/SE > 0.385) pipe wall calculations ?

Thank you

 

[mariolucas75]

OP,
ASME B31.3 don't provide Code equations when t ≥ D/6 or P/SE > 0.385.
You must be aware that at higher wall thickness, the stress across the wall thickness is no more a membrane stress (equal/average) but rather becomes exponential. ASME B31.3 Chapter K is based on High Pressure Piping definition that is based on a ASME B16.5 Class 2500 P/T rating.
Because the Piping Codes are drawn from ASME BPVC, a better response to your query can be found in Mandatory Appendix 1 Para 1-2 (Cylindrical Shells) of ASME Sec VIII Div1 that follows the rule in your query.
Both equations in Chapter K and Sec VIII Div 1 MA 1 are in exponential form.
You have already done the thickness calc per Chapter K. Can you also do the calc using Div 1 MA 1? It will be interesting to see the result.

Dear GD2,

Formula from ASME Div VIII Mandatory appendix 1, Para 1-2 for Cylindrical shells is the same as B31.3 Chapter XI, K304.1.2 Straight Pipe Under Internal Pressure and that gives me the thinner value for thickness rather than "conventional" thickness formula from 304.1.2 Straight Pipe Under Internal Pressure. Kindly see please attached file ...

 

[goutam_freelance]

With refined calculations using Matlab, the following results are found:

Allowable stresses for B31.1 and VIII-1 are the same.
VIII -1 MA1 gives a slightly lower thickness than B31.1
B31.3 gives the lowest thickness as the allowable stress is more.

 

[LittleInch]

Well 55mm would seem to cover most of the options.

Comprehensive check there so write it up and use that.

That is some gun barrel type pipe though - 420 bar! And 370C. Hope it isn't very long.

 

[mariolucas75]

My question (that i struggle with) still is - within B31.3:
Between B31.3 Chapter IX ("High pressure" thickness formula 34 a) and B31.3 Chapter II Par 304.1.2 Straight Pipe Under Internal Pressure ("Not High Pressure" thickness formula 3a) .... as shown in PDF in my previous submission?

Why B31.3 high pressure formula gives thinner wall thickness for pipe rather that B31.3 "Not high pressure" formula ??
Or what do I do wrong and can not get ??