Hydrocarbon Processing - January 2022 - 81

Heat Transfer
limit the heat gain from atmosphere with
an ambient temperature of 52.7°C. Client
specifications and NACE MR0175
limit the studs material grade to B7M and
L7M, which are directly exposed to sour
service environment or are in potential
exposure. Refer to Table A.4 from NACE
MR0175 (TABLE 1) for acceptable bolting
materials in wet H2
S service.
Solution. The client was approached
with the following recommended solution
(FIG. 1) in two steps. The first step
was adjusting the extent of insulation:
* Leaving the main girth flange joints
un-insulated. This would allow the
studs to be in direct exposure to
atmosphere and avoid the potential
exposure to sour service situation,
as in the insulated case.
* The calculated heat gain of
26°C and 32°C from the surface
temperature was 425 W/m2
329 W/m2
and
, respectively, considering
52.7°C as an ambient temperature.
Based on the proposed un-insulated
surface area at the tube and shell
sides, the maximum heat gain at the
tube side was 2,632 W: at 0.03%
of the exchanger duty, this was
insignificant. Since the exchanger is
installed in a modular structure and
contains enough obstructions from
direct sunlight, no solar radiation
impact was considered on uninsulated
surfaces.
* The un-insulated flange joint will
assist in early detection of toxic
H2
S gas in case of flange leakage.
The second step utilized alternate bolting
material (FIG. 2):3,4
* Based on minimum design metal
temperature (MDMT), the client's
standard restricts the bolting grade to
L7 for non-sour services. This stud
has a higher allowable stress by 25%
than L7M, but the size is still limited
to 64 mm by ASME Section II.
* The use of L7 studs results in a
flange OD of 3.7 m, which is again
not a reasonable size. An acceptable
recommended alternative was to use
the L43 grade, which has the same
strength as L7, but a higher sizing
limit to 100 mm. With this, the final
flange OD is 2.7 m and the complete
exchanger weight is 125 metric t.
This recommended solution will lead
to an eventual estimated savings of more
than $1 MM for each exchanger.
TABLE 2 gives a comparison of flange
dimensions designed per ASME Section
VIII, Div. 2, Class 1 with SA-350 LF2 Cl.
1 materials for different bolting material
grades for SA-320.
LITERATURE CITED
Complete literature cited available online at
www.HydrocarbonProcessing.com.
PANKAJ KUMAR SINGLA works
as a Senior Engineer at Worley in
Al-Khobar, Saudi Arabia. He has
more than 13 yr of experience in
the detailed engineering of static
equipment in the pre-bid phase,
as well as front-end engineering
design (FEED) and detailed engineering for various
oil and gas, petroleum refining and petrochemical
industry projects. Prior to joining Worley, Mr. Singla
worked as a Static Equipment Engineer for Fluor
Daniel India Pvt. Ltd., Daelim Industrial Co. (South
Korea) and as a Senior Engineer at Valdel Engineers
& Constructors (India). He holds a B. Tech degree
from Punjab Technical University, India. The author
can be reached at pankajsingla99@gmail.com.
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