Chemical Engineering November 2014 - 7

Letters
Facts at Your Fingertips: Forces
Acting on a Gasket
This letter is in reference to the article, Forces
Acting on a Gasket [Chem. Eng. October, 2014,
p. 32a]. I need to clear my understanding on the
seating stress required for the proper sealing.
As per the article, seating stress for the proper sealing
is indicated [see Equation (4) in the article]. This
formula provides the total/maximum bolt loads on the
gasket, which can be applied for the selected bolt size
and the material. This total bolt load may or may not
be suitable to provide minimum required force/load
for gasket seating and operating conditions.
Different codes and standards provide guidelines to
calculate minimum-required bolt load for the proper
sealing of the gasket joint. This minimum required
force depends on gasket properties (gasket seating
stress and factor) based on which, selection is made
for the number and the size of the bolts. Material
shall be obviously based on intended service.
I think that [Equation (4)] is not properly presented
in the article and should be corrected.
There are many references available in different
international codes and industry standards. One of
the worldwide used reference is ASME Sec VIII Div
1 (ASME Boiler and Pressure Vessel Code). Please
refer to mandatory Appendix 2 (Rules for bolted
flange connections with ring type gaskets), Sections
2-5 for the calculation of the bolt loads. Required bolt
loads for the proper sealing are to be checked for the
following two conditions:
1. Gasket Seating Condition: This is the minimum
required initial bolt load for the proper
seating at atmospheric temperature and
pressure and is a function of gasket properties
and the effective gasket or contact area
to be seated.
2. Operating Conditions: This is the minimum
load required to resist the hydrostatic end
force (for design conditions) on the area
bounded by the diameter of the gasket reaction
in addition to maintain sufficient compressive
load on the gasket for the proper sealing. This
is a function of design pressure, gasket properties
and the effective gasket area to be kept
tight under the pressure.
Sanjeev Shukla, Sr. Engineer-Mechanical
Engineering & Technology Department
PTT Exploration and Production Public Co. Ltd.
Bangkok, Thailand
Editor's note: We appreciate the comments and
added information. The above are excerpts of two letters
received on this topic. For the full text, and to
take part in the discussion, search the article title,
Forces Acting on a Gasket, on our website at www.
chemengonline.com
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Chemical Engineering November 2014

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