Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Flat end caps on a hydraulic cylinder

Flat end caps on a hydraulic cylinder

Flat end caps on a hydraulic cylinder

I am designing a hydraulic cylinder that will have a flat end cap and need to figure out the thickness it will need to be.  I was wondering if anyone could provide me with a formula?  The ID=6" and will be under a pressure of 3000psi.  TIA.

RE: Flat end caps on a hydraulic cylinder

The formula is in the ASME Boiler Code. The old formula was t = d x (K p / s)^0.5
d bolt PCD inch
p pressure psi
s unit stress psi
K 0.162 for plates bolted rigidly to flanges.

That should give you a start.
You should check the Code for the latest data and qualifiers.

RE: Flat end caps on a hydraulic cylinder

What would K be if the plate was welded and not bolted.

RE: Flat end caps on a hydraulic cylinder

K as given by johnp was anyway incorrect.
For a welded cap use the formula of johnp taking:
d=inner pipe diameter (cap should be inserted into the cylinder and the weld done on the extra cylinder length projecting beyond the cap, otherwise take the pipe outer diameter)
s=15000 psi (typical for low carbon steel)
If the cap may be welded also on inner side, the thickness could be slightly reduced (down to using K=0.2 if the cylinder wall is thicker than the minimum required) but this doesn't seem very important for such a small cap.
Of course you will require a heavy weld, with an effective depth equal to cap thickness.
Note that for your conditions (high pressure, small diameter) the code is quite conservative, especially for the weld.

Online tools for structural design

RE: Flat end caps on a hydraulic cylinder

Thanks for all the information.  I do have one more question though.  Does the s relate to the factor of safety and the yield strength?  I guess I would like to know how you figure out s or where does it come from.  Thanks again for all the help.

RE: Flat end caps on a hydraulic cylinder

The allowable stress per ASME VIII Div.1 is quite conservative, especially at room temperature.
As you don't want to use the code you might take 2/3 of the yield strength (except for very high strength steels).
For the weld you can calculate it in shear using an allowable shear stress equal to 70% of the allowable in tension.
All this is for building a prototype and testing it. Note that if you are designing an equipment that shall go to the market, you should hire someone to do a professional calculation.

Online tools for structural design

RE: Flat end caps on a hydraulic cylinder

I once got caught out with flat plate design.  I spent a lot of time studying the basic formula looking for escape.  However the case was settled out of court, much to my relief.  All the work I did I put on my website at www.gowelding.com in the section on welding calculations.  Its mind-blowing maths.  The thing to note is the maximum bending is at the edge of the plate and if the plate is welded it could bend the edge of the pipe.  BS5500 has a very complex formula for determining the stress at this point but ASME just uses spare thickness in the pipe.  

What I don’t understand is why the calculated stress can’t go up to 1.5 x design stress as the stress comes from bending? But no code that I know will allow this.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


White Paper - PLM and ERP: Their Respective Roles in Modern Manufacturing
Leading manufacturers are aligning their people, processes, and tools from initial product ideation through to field service. They do so by providing access to product and enterprise data in the context of each person’s domain expertise. However, it can be complicated and costly to unite engineering with the factory and supply chain. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close