Hydrocarbon Processing - October 2021 - 72
Heat Transfer
TABLE 2. Overstress plot points near the tube contact location
Case
Contact
angle, °
FEA model at
the tube hole
Overstress region
1
0-10
2
0-20
3
0-30
4
0-60
5
-5-5
FIG. 7. New design changes in the tubesheet holes.
6
40-50
expands, the tube will exert force on the ligament between the
tube holes as the tube tries stay in a straight position. This load
case simulated keeping the tube center line fixed by applying
MPC184 elements. The calculated stresses were very high,
which may have caused the tubesheet failure.
Tubesheet coils at the end of the tubesheets (plated con7
85-95
struction
with refractory) have fixed connections, while the
intermediate tubesheet coils are only supported (rested) and
free to move in the tubesheet holes. This causes relative thermal
expansion/displacement of the tubes during heater startups,
ramp-ups and shutdowns.
The tubesheet is supported above the first tube row. Dur8
130-140
ing
thermal expansion, there is sufficient clearance for thermal
expansion, which will not cause stress concentration near the
support point location. In addition, during axial movement of
the tubes, the bottom tube row acts as a cantilever and bending
stresses occur in the bottom tube row ligaments.
The heater bottom tubesheet has convection coils that carthe
bottom row of the tubesheet (FIG. 6). The high temperature
causes a higher expansion of the bottom row than in any other
parts of the tubesheet. At elevated temperatures, allowable stress
values are reduced and cause overstress in the ligaments-the
ambient temperature considered for the FEA analysis was 35°C.
To check for the possibility of tubesheet failure due to
expansion, tubesheet expansion with various tube rest locations
in the tubesheet hole was simulated. For a conservative
scenario, the tube positions were fixed. When the tubesheet
72 OCTOBER 2021 | HydrocarbonProcessing.com
ry two-phase fluid, which causes flow-induced vibrations during
operations, especially during initial startups. Simulations
for these loads were performed and found that the stresses are
negligible and cannot play a major role in the tubesheet failure.
Case study. Tubesheet expansion in the direction of its length
and the relative position of the tubes may be the reason for failure.
A case study was performed for various tube resting positions-as
might have happened during initial heater construction
and subsequent tubesheet/coil replacement and/or also
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Hydrocarbon Processing - October 2021
Table of Contents for the Digital Edition of Hydrocarbon Processing - October 2021
Contents
Hydrocarbon Processing - October 2021 - Cover1
Hydrocarbon Processing - October 2021 - Cover2
Hydrocarbon Processing - October 2021 - Contents
Hydrocarbon Processing - October 2021 - 4
Hydrocarbon Processing - October 2021 - 5
Hydrocarbon Processing - October 2021 - 6
Hydrocarbon Processing - October 2021 - 7
Hydrocarbon Processing - October 2021 - 8
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Hydrocarbon Processing - October 2021 - 86
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Hydrocarbon Processing - October 2021 - 89
Hydrocarbon Processing - October 2021 - 90
Hydrocarbon Processing - October 2021 - Cover3
Hydrocarbon Processing - October 2021 - Cover4
Hydrocarbon Processing - October 2021 - GP-1
Hydrocarbon Processing - October 2021 - GP-2
Hydrocarbon Processing - October 2021 - GP-3
Hydrocarbon Processing - October 2021 - GP-4
Hydrocarbon Processing - October 2021 - GP-5
Hydrocarbon Processing - October 2021 - GP-6
Hydrocarbon Processing - October 2021 - GP-7
Hydrocarbon Processing - October 2021 - GP-8
Hydrocarbon Processing - October 2021 - GP-9
Hydrocarbon Processing - October 2021 - GP-10
Hydrocarbon Processing - October 2021 - GP-11
Hydrocarbon Processing - October 2021 - GP-12
Hydrocarbon Processing - October 2021 - GP-13
Hydrocarbon Processing - October 2021 - GP-14
Hydrocarbon Processing - October 2021 - GP-15
Hydrocarbon Processing - October 2021 - GP-16
Hydrocarbon Processing - October 2021 - GP-17
Hydrocarbon Processing - October 2021 - GP-18
Hydrocarbon Processing - October 2021 - GP-19
Hydrocarbon Processing - October 2021 - GP-20
Hydrocarbon Processing - October 2021 - GP-21
Hydrocarbon Processing - October 2021 - GP-22
Hydrocarbon Processing - October 2021 - GP-23
Hydrocarbon Processing - October 2021 - GP-24
Hydrocarbon Processing - October 2021 - GP-25
Hydrocarbon Processing - October 2021 - GP-26
Hydrocarbon Processing - October 2021 - GP-27
Hydrocarbon Processing - October 2021 - GP-28
Hydrocarbon Processing - October 2021 - GP-29
Hydrocarbon Processing - October 2021 - GP-30
Hydrocarbon Processing - October 2021 - GP-31
Hydrocarbon Processing - October 2021 - GP-32
Hydrocarbon Processing - October 2021 - GP-33
Hydrocarbon Processing - October 2021 - GP-34
Hydrocarbon Processing - October 2021 - GP-35
Hydrocarbon Processing - October 2021 - GP-36
Hydrocarbon Processing - October 2021 - GP-37
Hydrocarbon Processing - October 2021 - GP-38
Hydrocarbon Processing - October 2021 - GP-39
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Hydrocarbon Processing - October 2021 - GP-44
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