18" id x 22" od 4140 annealed tube heat treating

[Schroyer]

We are building four 18" ID x 22" OD cylinders that require 5:1 safety factor at 2500 psi. The material sourced is a 4140 annealed tube with a mill cert yield strength of 62ksi. We have excess material on the ID to bore and hone the cylinder straight, but on the OD the mill specs say it could be 0.285" out of straight on our 12' length. Therefore, the wall thickness could be down to 1-3/4" on the tube in some locations. This would give me a 4.8:1 safety factor.

Can this material be heat treated prior to machining without distorting it too much? Is an 80 ksi yield strength obtainable with heat treating? The minimum yield I would like to see is 70ksi. Any ideas will be appreciated.

 

[metengr]

Schroyer;
What are the service conditions for these cylinders with this kind of design margin?

The reason I am asking is because you can either purchase pipe material to an ASTM specification that controls dimensions, heat treatment and provides inspection requirements to ensure defect-free or sound material or you can deal with a random length of a hollowed round, supplied as 4140 steel from a steel distribution center and subject it to a battery of mechanical tests and NDT.

If you go the route of an ASTM pipe specification, you will need to increase the wall thickness because of the lower tensile yield strength with the offered grades in A 335 or A 369 or other specification.

If you go the route of using a hollow 4140, you can send it to a heat treater and have a normalization heat treatment performed with no temper. This should result in a tensile yield strength well above 65 Ksi, probably closer to ~85 Ksi.

The trade off I see versus using an ASTM pipe specification is that you should have the 4140 hollow meet the general requirements of ASTM A 999, which is "General Requirements for Alloy and Stainless Steel Pipe".

 

[unclesyd]

The first two are for people who can supply cylinder components.
The third and fourth are to suppliers that offer honed tube/pipe.

http://www.hydratechglobal.com/en/portfolio.html

http://www.crconline.com/Components/catalog.html

http://www.arcelormittal.com/tubular/images/ArcelorMittal_DOMBro.pdf

http://www.tubesupply.com/services.htm

 

[Schroyer]

The reason for the high factor of safety is the cylinders will be used to lift a heavy machine, and there will be people around, and sometimes under the load.

Thank you for the responses so far.