Hydrocarbon Processing - June 2022 - 85

Heat Transfer
K. DARU, Air Products and Chemicals Inc.,
Houston, Texas; A. PANCHAL, Independent
Consultant, Mumbai, India; and P. GALA,
Reliance Industries Ltd., Mumbai, India
Uncommon lessons: Shell-and-tube
heat exchangers-Part 2
Shell-and-tube heat exchangers
(STHEs) are the most common heat
transfer process equipment in all types
of industrial plants. Due to the variety of
available construction options, an STHE
can be suitably designed for most processes
and design conditions and can be
constructed from different materials or
combination of materials.
Part 1 of this article (published in
the April 2022 issue) began the focus
on specific types of lessons and design
limitations that none of the commercial
design programs (software, Excel
spreadsheets, etc.) will identify with
their " help " menus or warnings. Merely
checking drawings with respect to design
calculations is insufficient to ensure
thorough compliance and reliable product
design that will operate (thermally
and mechanically) as intended.
The authors' purpose is to shed light
on those uncommon but valuable lessons
that are not discussed in reference
manuals or design guides. These lessons
will be helpful in engineering and design
activities.
Sleeve welded to the inner torus of
an expansion bellow. An expansion
bellow is a flexible element and the knuckled
(torus) section of the bellow is a highly
stressed region. The torus sections of the
expansion bellow are responsible for the
flexible behavior of the joint in service.
The welding of clips (like the liner
or sleeve) on the torus section should
be avoided because it increases the effective
stiffness of the expansion bellow.
With stiffeners attached to the knuckled
sections, the joint requires more bending
force or longitudinal movement to flex
the bellow-this may not exist based on
the estimated differential thermal expansion-and
this can result in overstressing
the tube-to-tubesheet joint.
In earlier ASME Code1
editions (before
2015), no explicit guidance was available
on whether it was possible to weld
sleeves on the torus regions, or, if it was
possible, what the maximum sleeve thickness
was that could be welded. A query
was submitted to the code, and it now has
incorporated guidance on the maximum
thickness of the sleeve that may be welded
on the annular portions of the bellows.
Exchangers constructed prior to 2015
were provided with internal sleeve construction
based on the vendor's engineering
experience and/or judgement, as no
guidelines were available in the applicable
ASME Code editions.
The authors encountered sleeve constructions
(as shown in FIG. 5A) for an
exchanger designed and constructed per
the 2015 edition of the ASME Code1
in
Sleeve
Sleeve
Expansion
below
which no requirements for sleeve provisions
were specified. As the thickness
of the sleeve was not limited by Code,
sleeves were provided without considering
the impact of welding these sleeves on
the performance of the bellows.
In the 2017 edition of the ASME
Code, a paragraph was introduced that
permitted welding the sleeve to the bellow,
if required, with specific thickness
limitations. In many cases, the thickness
limitation per the ASME Code may be
difficult to meet for practical reasons. For
such situations, an alternate arrangement
is used by introducing a transition piece
that eliminates welding of the sleeve to
the expansion joint, as shown in FIG. 5B.
Impingement rods. As per API Standard
6603
, impingement rods should be
supported on both ends and not attached
to the tubesheet by welding alone. For
proper strength, the impingement rods
must be primarily tapped inside the
Sleeve
Transition piece
Expansion
below
Weld
Welded to
transition piece
A
B
FIG. 5. Arrangement of a sleeve for an expansion bellow.
Hydrocarbon Processing | JUNE 2022 85
Hydrocarbon Processing - June 2022

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