Compound Cylinder
Compound Cylinder
(OP)
I am constructing a compound cylinder to withstand an internal pressure of 6,000 psi.
The construction is from two pipes
Inner pipe material seamless Stainless Steel 316
ID = 4.00”
OD = 4.25”
Wall thickness = 0.125”
Outer pipe material seamless Steel 1018
ID = 4.375”
OD = 6.625”
Wall thickness = 1.125”
Both ends of the 48” long cylinder to be closed by 1.25” thick flanges with proper seals.
There is a gap of 1/16” between the inner and outer pipe. I propose to fill this gap with a high strength epoxy.
As per the Barlows formula, the outer pipe bursting pressure works out to be 24,000 psi. This gives a safety factor of 4 for a working pressure of 6,000 psi.
I request your suggestions regarding the construction and any design flaws.
Thanks
The construction is from two pipes
Inner pipe material seamless Stainless Steel 316
ID = 4.00”
OD = 4.25”
Wall thickness = 0.125”
Outer pipe material seamless Steel 1018
ID = 4.375”
OD = 6.625”
Wall thickness = 1.125”
Both ends of the 48” long cylinder to be closed by 1.25” thick flanges with proper seals.
There is a gap of 1/16” between the inner and outer pipe. I propose to fill this gap with a high strength epoxy.
As per the Barlows formula, the outer pipe bursting pressure works out to be 24,000 psi. This gives a safety factor of 4 for a working pressure of 6,000 psi.
I request your suggestions regarding the construction and any design flaws.
Thanks





RE: Compound Cylinder
RE: Compound Cylinder
It is for internal use as an accumulator for the working of other components in a prototype system.
RE: Compound Cylinder
RE: Compound Cylinder
Another problem I can see is the large change in section thickness where the 1.25" thick end flanges attach to the .125" thick walls of the inner cres tube.
Lastly, with a high pressure hydraulic cylinder the stiffness of the cylinder walls can be of more importance than the simple stress in the cylinder walls. If there is significant deflection in the cylinder walls from high pressures, it can cause problems for the piston seals.
RE: Compound Cylinder
The bore or outer dia need not be machined, so making one piece from 316 was the cost consideration and availability of standard hollow bar, tube or pipe.
The alternative I considered was to fill the gap with hydraulic oil and pressurise from the same source as internal pressure, so that the inner and outer pressure of the stainless steel pipe always remain the same.
RE: Compound Cylinder
I make this recommendation because it is highly likely that there are failure modes that you have not considered that could (potentially) come back to bite you in the proverbial... If/when it blows up and injures or kills someone or does some significant property damage, you want to be able to tell either your insurance company or the courts that you followed an internationally-recognized Code/Standard as opposed to just winging it.
RE: Compound Cylinder
As per this code, the wall thickness required is 0.8”, whereas my outer pipe is 1.125” thick.
Please allow me to ask another question:
For the inner stainless steel pipe with a thickness of 0.125”, the bursting pressure is 4,000 psi.
If I pressurize the inner pipe slowly, it will start expanding on reaching the yield pressure of 500 psi and with further increase of pressure the circumference will start expanding.
As the original gap between the pipes is 1/16”, the circumference will increase by 2.95% only before it touches the inner surface of thick pipe.
In your opinion, will the inner pipe burst before touching the outer pipe?
If not, will the stainless steel pipe act as lining to the outer thick pipe?
RE: Compound Cylinder
RE: Compound Cylinder
RE: Compound Cylinder
leaving a gap for the inner liner to yield and then collapse would break it in a few cycles and is a bad idea IMHO
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Compound Cylinder
Why do you want a stainless Liner?
If this is an accumulator and you need SS for some reason I see two options.
1. make it solid stainless, much easier and less prone to issues
2. use a thin SS liner and expand it tightly into the outer cylinder
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