Choose Material Allowable Stress

[elhamydy]

Hi All

-Firstly How to choose the yield strength ,allowable stress for design and allowable stress for hydrostatic test in table 5.2a note that we found many material with the same value (design temperature less than 93°C)

-Secondly How to choose the yield strength ,allowable stress for design and allowable stress for hydrostatic test in table 5.2a note that we found many material with the same value (according to ANNEX M)

Best Regards

 

[JStephen]

Check with local fabricators, steel service centers, or mills to see what is most commonly used and available.
In the US, for small to medium tanks, that will usually be A36 or A36-Mod. A516-70 is available for larger tanks. A516-60 is available to some extent for cold-temperature applications.
But the grades commonly used vary internationally.
Also check on available widths and lengths.
For a very large tank or for multiple tanks, you may have more options by placing a mill order.
Usually, it will be left to the tank fabricator to select the most efficient grade and plate dimensions to be used.

 

[IFRs]

API 650 has a table of product and hydrotest allowable stresses for a variety of materials. Can you use one of those?

 

[elhamydy]

Thanks for reply
How to choose the yield strength ,allowable stress for design and allowable stress for hydrostatic test in table 5.2a note that we found many material with the same value (design temperature less than 93°C)
Example
As per table 5.2a
yield strength Sd St
A841M 345 194 208
A841M 345 196 210
A841M 345 188 201
Best Regards

 

[IFRs]

In table 5.2, there are only two entries for A841M - Class 1 and Class 2. But yes, other materials have similar or the same strengths. For all materials, see table 4.4 for the API Group number, and some notes on each. The Group number is used in Figure 4.1. When choosing materials, I try to choose common grades that are readily available while avoiding grades that require thermal stress relief see 5.7.4 ( Group IV and above ) and staying under 50,000 psi yield stress. PWHT is or can be expensive, avoiding PWHT and using under 50ksi make future API 653 repairs less expensive. Also see section 5.5 which required annular plates (adding cost) when the shell is high strength or Grade IV and above. Also see section 4.2.2 - some grades have lower maximum thickness limits. It is also convenient to have the shell plate and nozzle neck strengths similar or at least not too far apart, see 5.7.2.3.e. There is more but that's a start.