High strength metals for external pressure vessel
High strength metals for external pressure vessel
(OP)
I have to design a corrosion resistant cylindrical pressure vessel that withstands high external pressures. I am limited to a certain wall thickness which, according to testing already performed, is insufficiently strong if the tube is made out of stainless steel. There is some machining required in reaming the ID of the tube to tolerance to accept an O-ring plug. What material options do I have to improve the pressure rating? Inconel, titanium? Any other suggestions? Again, the ends of the tube need to be machined to an ID tolerance spec and roughness spec to accept the O-ring plugs, so the material should be relatively easily machinable, or at least not impossibly difficult to machine. Thanks!





RE: High strength metals for external pressure vessel
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: High strength metals for external pressure vessel
i don't think Ti will do better than high strength steel.
what about a thin Ti inner sleeve wrapped with graphite ??
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
The external pressure is 10,000+ psi.
rb1957,
Why wouldn't Ti outperform steel? The tensile/compressive strength is several times higher.
RE: High strength metals for external pressure vessel
looking at things, p = 10000psi (give or take), R = 1" ...
stress = pR/t = 10000/t
125000 = 10000/0.08 ... sounds pretty thin, but onlu 1"radius ... maybe (on the road, haven't got my books for buckling a cyclinder from pressure)
RE: High strength metals for external pressure vessel
For an external pressure of 10,000psi, and an OD of 2.00",
a perfect tube will resist collapse with a wall as follows:
316 .105"
Ti6Al4V .120"
for the same conditions,
an imperfect tube with a radial deviation of .005"
will resist collapse with a wall as follows:
316 .336"
Ti6Al4V .127"
I could be holding my tongue wrong...
Mike Halloran
Pembroke Pines, FL, USA
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
How did you reach those results?
And how is the 316 SS tube stronger than Titanium as would be implied by the thinner wall requirement to withstand 10,000 psi?
We're just talking von Mises stress (equivalent tensile stress) in the material created by the external pressure, and the tensile yield stress for Ti is much higher than SS, about quadruple (130 vs 30 ksi). Correct me if I'm wrong...
cloa,
I mean external pressure as if the tube was submerged in water.
rb1957,
I'm referring to stainless actually.
And stress = pr/t is valid for INTERNAL pressure vessels as far as I know...
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
ref 1: "Tubing Limits for Burst and Collapse", Tech Note, CTES, L.C., Conroe TX www.ctes.com
ref 2: "Effect of Initial Eccentricity on Collapse Pressure of Circular Beam Tubes", S. Yadav
Fermi National Accelerator Laboratory, Batavia IL www.flab.gov
Ti6Al4V properties from http://ti
I did a goal seek for wall thickness based on 10,000 psi as the critical collapse pressure, for circular and oval tubes.
The spreadsheet has given results that correlate well with an unfortunate incident in a former employer's shop a while ago, and that also correlate with results reported here in another discussion.
I'd rather not make it public, not least because I don't have a lot of confidence in the numbers I used for Ti6Al4V's properties; yield stress, tensile modulus and shear modulus. If anybody has trustworthy numbers for those, please speak up.
Mike Halloran
Pembroke Pines, FL, USA
RE: High strength metals for external pressure vessel
The listed values for shear modulus and elastic modulus yield a computed Poisson' ratio of 0.29, but Matweb lists Poisson's ratio as 0.342. The buckling calculations are highly sensitive to the ratio. So, what to believe?
Mike Halloran
Pembroke Pines, FL, USA
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
Mike Halloran
Pembroke Pines, FL, USA
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
For example,
2 2 in od of tube
0.120 0.120 in wall thickness
316L Ti-6Al-4V
2.70E+07 1.70E+07 psi Elastic modulus
1.06E+07 6.39E+06 psi Shear modulus
0.27 0.33 Poisson's ratio
2.70E+04 1.32E+05 psi yield point for tube material
15179.3 9922.5 psi critical buckling pressure for a _perfect_ tube
0.005 0.005 in radial deviation from circle at worst point
2668.73 8667.60 psi critical pressure for collapse of imperfect tube
(Numbers pasted from a spreadsheet and edited; I hope they line up for you.)
Mike Halloran
Pembroke Pines, FL, USA
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
look up (google) MIL-HDBK-5, you can easily get 160-180 ksi (ftu, that is,) steels; fcy >100ksi (i think). High Strength Steel should be cheaper than Titanium, and similar (or stronger even; 300M, ftu = 280ksi) than Ti (6Al4V for example, ftu = 160ksi).
i believe pr/t works for external pressures too, only the resulting stress is compression.
RE: High strength metals for external pressure vessel
I need a metal with good corrosion resistance. Stainless steels are much weaker as far as I know. Correct me if I'm wrong please.
RE: High strength metals for external pressure vessel
It is only when you get to plastic buckling where the yield and ultimate strengths start to play a role. In most applications, it is elastic buckling that will dominate, so high strength or low strength will make no difference...
RE: High strength metals for external pressure vessel
RE: High strength metals for external pressure vessel
i think this is a very long cyclinder ... (L/r)^2 >5r/t
L = 24", r = 1", t =0.1" ... 576>50
then fcr = nu*0.25*E/(1-u^2)*(t/r)^2
nu is a plasticity correction, call it 1
u is poission's ratio, call it 0.3
fcr = 0.25*30E6/(0.91)*(0.1/1)^2 = 82ksi
pr/t = 10000/0.1 = 100ksi
so you'd need more than 0.1" thick of a stainless steel with fcy > 100ksi (@ 200C, something like 80% of RT)
t = 0.12, fcr = 111ksi, pr/t = 83ksi