collapse pressure for housings/tubing

[aroundhere]

Ive been designing stainless, inconel and steel housings for years up to 15-000 to 30,000 psi external pressure @ 350F or more degrees. I have always used the API 5C Yield strength collapse formula and this formula has always been spot on. I havent worked with titanium other than a few small parts. Well, I require a titanium housing. Here is my issue. Titanium has a elastic modulus of roughly half of steel(16.5). I believe I need to use elastic formula in this spec, but the numbers are too high. Ti 6AL4V with a yield strength of 120ksi seems suitable, but I am fairly certain I cannot use the yield strength formula to calculate pressure. Also, looking at the 6al4v curve, the yield strength drops from 120 ksi to 90ksi when nearing 350F, but I can work around this if this is indeed true. Given the yield strength equation(using 120ksi), collapse for a 2.50 od x 2.00 id is around 22,000psi. I have yet to find an equation for elastic collapse that yields results that are believable. Also, BeCu25 has a low elastic modulus (maybe 18.5)....I've never had an issue with this material either. Young's modulus being half of steel is what I am concerned about and if the housing changes from a collapse to more of a buckling situation. I suppose I will have to do testing to know, but if anyone has already already been down this road or could point me in the right direction, it would be great to have input.

thanks

 

[racookpe1978]

How big is the titanium housing?

How thick is the wall (the walls ?) relative to the whole assembly and to the "unsupported length between the ends?

What i am suspicious of - but can't confirm without dimensions - is that the complex failure mode if a small thick-walled "box" or "tube" is going to behave very differently than a long thin tube with two "simple" ends like a sausage.

External pressure? "15-000 to 30,000 psi external pressure @ 350F or more degrees. "