Question about long term/short term stress in 316SS...
Question about long term/short term stress in 316SS...
(OP)
This webpage says that 316H has a "short time" tensile strength of 120MPA at 900C.
It also says that for a creep of less than 1% in 10,000 hours at 800C the pressure should be kept below 20 MPA.
http://www.askzn.co.za/tech/tech_grade_316.htm
Could someone explain the relevance of these numbers in the context of a pressure vessel.
Thanks.
It also says that for a creep of less than 1% in 10,000 hours at 800C the pressure should be kept below 20 MPA.
http://www.askzn.co.za/tech/tech_grade_316.htm
Could someone explain the relevance of these numbers in the context of a pressure vessel.
Thanks.





RE: Question about long term/short term stress in 316SS...
In your previous post regarding ASME and pressure vessels you have the necessary information to seek outside expertise. Without getting too in depth, the suitability of materials for use in pressure vessels must consider the following;
-tensile/yield strength at service temperature
-time dependent properties like creep deformation or stress rupture
-fatigue
and corrosion
The ASME B&PV Code evaluates and endorses materials for use at maximum service temperatures. These materials are permitted to be used in boiler and pressure vessels. In general, ASME B&PV Code provides rules for design, and also one can design by analysis for pressure vessels.
RE: Question about long term/short term stress in 316SS...
The reason is at this temperature and above the metal will deform slowly with time, and at stresses much lower than the short time tensile or yield strength. Stress is no longer proportional to strain, time is now involved.
One might say Hooke's Law was repealed above roughly 540-600C.
The good news, which I presume you already know, is that ASME publishes tables of allowable design stresses for 316H and other alloys, for different temperatures.
Your next problem will be actually finding 316H available somewhere.
James Kelly
www.rolledalloys.com
RE: Question about long term/short term stress in 316SS...
As far as 316H and 316, I've been told that we can safely substitute some 316s for 316H, it depends on the composition. Care to comment on that ?
RE: Question about long term/short term stress in 316SS...
I looked at the allowable stress values for 316 and 316H in plate form under SA-240. Both have comparable allowable stresses at 1500 deg F. Keep in mind that this is the upper limit for design use of this material (1.3 Ksi) and I would not recommend using this material unless you are willing to substantially increase the wall thickness to reduce your service stresses to well below 1.3 Ksi. This will increase the cost of material. I believe you need to re-evaluate your use of 316 material for this application.
RE: Question about long term/short term stress in 316SS...
The material cost isn't an issue for the test vessel, but it will be for the real vessel. See my post on insulating the vessel walls and water cooling it.
RE: Question about long term/short term stress in 316SS...
If I am wrong on this, please tell me.
RE: Question about long term/short term stress in 316SS...
I know that the lower C material usually makes the mechanical properties at room temp, and even short term high temp. But without the C you will not get the same creep/stress rupture results. Often alloys have higher strength because of nitrogen, this does not help out at high temp.
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