Allowable Stresses, Sd/St for Titanium Tank 3

[sxz]

HI, for titanium tank, material B-265 Gr.2, design temperature 261F, can we use the Sd at, 20,600 psi, it is 70% of its yield, 29,700psi? (ASME 8-1 has 12,400 psi). Thanks for any comments.

 

[MJCronin]

This is yet another, "Do I have permission from eng-tips to pick and chose trules from various codes ?"

What type of tank is this ?.... What is your code of record ?... API-650 ?... API-620 ?.. Something else ?

What is the design pressure ?

Give us a complete description of what you are trying to do ... not a tiny window ....

MJCronin
Sr. Process Engineer

 

[sxz]

MJCronin,

Thank you for your reply.
It is API 650 tank, Design pressure: 0.1 psig. Dimensions ID 40 feet, Height 46 feet, Cone roof. API 650 doesn't cover titanium material, I refer the stress ratio from Appendix S, Table S2.b, and get Sd = 20600 psi. St=36000, B265 Grade 2 has yield: 40,000 psi, tensile: 50,000 psi.

 

[JStephen]

The stainless steels in Annex S generally have low yield and high ultimate strengths, relatively speaking, and use allowable closer to yield than would be otherwise allowed. The yield/ultimate of your material do not fit that well. I would consider looking at the CS and aluminum requirements to see how they compare as well.
Ultimately, this should be a contractual issue, as you're building a non-code tank.

 

[HTURKAK]

The subject tank is out of scope of API 65o for temperature and material so , will not be API 650 tank. However, you may follow the standard.

Regarding the Allowable Stress , pls look clause 5.6.2 ..

5.6.2.1 The maximum allowable product design stress,....... The design stress basis, Sd, shall be either two-thirds the
yield strength or two-fifths the tensile strength, whichever is less.
5.6.2.2 The maximum allowable hydrostatic test stress, St,..... The hydrostatic test basis shall be either three-fourths the
yield strength or three-sevenths the tensile strength, whichever is less.

My opinion..







Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[sxz]

HTURKAK,

Thank you for your input, if applying the Clause 5.6.2, Sd will be 16,000psi, St will be 21,000 psi.

 

[MJCronin]

JStephen gives good advice ... Your TI tank is just one step outside of API-650... and because of that..

I strongly suggest that you include the design methodology as an Appendix to your contract documents

If your client wants you do something different, he can say so officially ...

(BTW, I suggest that you develop cost estimates for each and every allowable stress methodology)

Dumb question: If you adopt an aggressive approach (high allowable stress) to design, will you run into fabfrication problems as thin walled Titanium/Stainless steels become much more difficult to weld ?

MJCronin
Sr. Process Engineer