×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Jobs

external pressure calculation for pressure vessel
2

external pressure calculation for pressure vessel

external pressure calculation for pressure vessel

(OP)
while calculating the thickness in case of external pressure we use graph from sec II part D for calculating the allowable stress.
In any case suppose if we require to calculate the allowable pressure in case of compression how can we take the allowable stress value for carbon steel in case of compression?

RE: external pressure calculation for pressure vessel

As you mention "sec II part D" it's apparent you are referring to ASME Boiler and Pressure Vessel Code, and likely Section VIII application.

See VIII-I UG-23(b) for "the maximum allowable longitudinal compressive stress to be used in the design of ...". The method determines factor "A" and then you go into the charts of II-D for allowable stress.

RE: external pressure calculation for pressure vessel

2
From a pure mechanical engineering perspective - it is important to understand that failure due to compression is completely different from failure due to pressure/tension.

Therefore, for internal pressure / tension, the failure mode is burst, which is governed by yield and ultimate strengths. For external pressure / compression, the failure mode is buckling, which is generally governed by the Young's Modulus, and geometric factors.

Once you understand these important distinctions, then the rules to be followed will make more sense.

RE: external pressure calculation for pressure vessel

(OP)
Thanks for the replies gentle man
But my concern is still the same. Actually I have to design a long horizontal pressure vessel(18000mm) where thickness due to internal pressure is coming out to be 7 mm but in case of external pressure it is coming out to be 17 mm for which I need stiffeners. What I want to know is that while calculating the thickness required due to external pressure do we have allowable compressible stress like the allowable tensile stress as mentioned in sec II part D.
will the case of buckling come here TGS4 sir?

RE: external pressure calculation for pressure vessel

If you are designing a vessel to ASME Section VIII, Division 1 then you should follow the rules provided therein. The answers you seek are there, if only you follow the rules.

RE: external pressure calculation for pressure vessel

rajeev383: It seems like you are looking for exactly what TomBarsh has replied. VIII-Div.1 UG-23 provides guideline about both allowable tensile stress and allowable compressive stress. Refer UG-23(b)for allowable compressive stress. Rest all please correct me if I am wrong, this allowable compressive stress is what used to design vessel for external pressure, its one and the same thing based on context TSG4 explained. And these allowable compressive stresses are in chart form in PART-3 of Sec II-D.

Since, the question was completely replied already, this is just a small attempt to break down the replies to very basic level based on rewritten question by rajeev383.

rajeev3873: Hope this clarifies.

Thank you TSG4 & Tombarsh for your luminary responses on many queries.

RE: external pressure calculation for pressure vessel

rajeev383, when you calculate a cylinder to external pressure per ASME VIII, there is no such thing as an allowable stress under compression. The allowable calculated per UG-23 is for longitudinal compression, whilst in a cylinder you are interested in circumferential compression.
You need to follow the procedure starting at UG-28 to make the check. Other codes have different procedures and could give you a formula for the allowable compressive stress (still strongly dependent on geometry of course).

prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads

RE: external pressure calculation for pressure vessel

also see Case 2286-5
Alternative Rules for Determining Allowable External
Pressure and Compressive Stresses for Cylinders, Cones,
Spheres, and Formed Heads
Section VIII, Division 1

Regards
r6155

RE: external pressure calculation for pressure vessel

As info, CC 2286 is on rev. 6 as of a few months ago.

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!


Resources