Chemical Engineering February 2017 - 52

are bolted separately to the external tailpipe
spool, such that all gaskets in the flanged
design are accessible from the exterior of the
exchanger without removing the tube bundle.
Some of the advantages and disadvantages
for this type of configuration are listed below:
Configuration 3 advantages:
* In this configuration, there is no gasketed
joint inside the shell cover. This avoids the
risk of intermixing of fluids inside the shell
cover
* Gasket 1 is used to seal the tube-side
fluid flow toward the inner set of bolts on
Flange 1, and Gasket 2 is used to seal the
shell-side fluid flow toward the inner set
of bolts. This two-gasketed joint arrangement
helps to avoid intermixing between
the shell-side and tube-side fluids
* The inner set of bolts on Flange 1 can be
released from outside the exchanger to detach
the bellow assembly from shell cover
Configuration 3
of
the
flange
joint
has
the
advantage of having no gasketed joint inside the
shell cover. This avoids intermixing of fluids inside
the shell cover
* The outer set of bolts on Flange 3 can
be released from outside the exchanger
to detach the external piping spool from
heat exchanger, allowing access to all
three gaskets for inspection without removing
the shell cover
* No manway or inspection opening is
required in the shell cover to access the
bellow's assembly for installation
* A relatively shorter shell cover is possible
compared to the other two configurations
described here.
* Configuration 3 disadvantages
* With Configuration 3, the bellow assembly
needs to be cut and re-welded for
replacement
* The design of special Flange 1 is complex.
It has two gaskets under different
design conditions and one set of bolts
* The design of special Flange 3 is also
complex. It has two sets of bolts and
three gaskets. Both special flanges have
to be designed according to best mechanical
judgment, because this type of
construction is not covered in any code or
standard
* Bellow cannot be inspected without removing
complete shell cover.
52
Challenges for special Flange 3
There are a host of challenges associated
with finalizing the design of the special flange
3 in configuration 3. It is imperative to note
that with this flange, the innermost gasket
(Gasket 1) is exposed to tube-side design
conditions, while middle gasket (Gasket 2)
and outermost gasket (Gasket 3) are exposed
to shell-side design conditions. The
flange does not fit into any code-specific
configuration, and finite-element analysis of
such shapes with complex design conditions
is nearly impossible. Manual calculations,
by using modified formulas for flange
design from an existing design code, can be
one of way to complete mechanical strength
calculations. Different users may adopt other
ways to perform calculations based on their
best mechanical judgment.
Major challenges for this flange design will
be in finalizing the gasket-load reaction diameter
" G " and the bolt circle diameter " C "
for this calculation, because the three gaskets
have three different values of " G " and
the two sets of bolts give different lengths of
lever arms to calculate moments in operating
and gasket-seating conditions. For the gasket-seating
condition, the minimum required
bolt load can be easily calculated using all
three gasket parameters.
Higher design temperature from both
sides can be adopted as flange design temperature.
Another challenge will be to calculate
minimum required bolt load for the
operating condition, because different portions
of the flange are exposed to different
design pressures.
After some iteration, engineers can arrive
at a working design that is acceptable to
local authorities and to the American Society
of Mechanical Engineers, as applicable. n
Edited by Scott Jenkins
Reference
Tubular Exchanger Manufacturer's Assoc., TEMA Standards, 9th ed., Tarrytown,
N.Y., www.tema.org.
Author
Pankaj Kumar Singla is a mechanical design
engineer for Fluor Daniel India Pvt. Ltd. (6th
Floor, Infinity Tower B, Cyber City, DLF City
Phase II, Gurgaon 122 002, Haryana, India;
Email:
pankajsingla99@gmail.com; Phone:
+91-97164-14125). Singla has more than
eight years of experience in detailed engineering
of static equipment in the pre-bid phase,
as well as front-end engineering design and
detailed engineering for various oil and gas,
petroleum refining and petrochemical industry projects. Prior to joining
Fluor, Singla worked for Daelim Industrial Co. (South Korea) and
Valdel E&C (India). He holds a B. Tech. degree from the Giani Zail
Singh College of Engineering & Technology, Bathinda, Punjab, India.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
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Chemical Engineering February 2017

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