Hydrocarbon Processing - December 2020 - GP-30

HEAT EXCHANGE

Safely design brazed aluminum heat
exchangers to avoid thermal shock
I. HUSSAIN, OQ, Muscat, Oman

Although brazed aluminum heat exchangers (BAHEs) are designed per
American Society of Mechanical Engineers (ASME) Pressure Vessel Code
Section 8, they are still very sensitive to
temperature fluctuations. The corrugated aluminum plates are tightly brazed
with one another, and they expand and
contract together. This expansion/contraction between the corrugated plates
or other parts of the BAHE can be disproportionate if the rate of temperature
change is high, resulting in metal fatigue
and possible cracks or leaks.
The material will be slightly deformed
due to these external forces. If these forces are lower than its yield strength, then
the material will return to its original
shape as the forces are removed. However, if these low forces due to temperature changes are repeated regularly, then
the material can be thermally fatigued
and cause fatigue cracking. Process fluid

can leak to atmosphere or adjacent layers
from these cracks.
If the brazing joints between the fins
and cap sheet fail due to thermal fatigue, it
will increase the stresses on adjacent joints
and cause a possible chain failure on the
fin matrix. This chain reaction can result
in sudden rupture at an operating pressure that is less than the design pressure. It
means that the BAHE passes must be depressurized by removing the process fluid,
which would help reduce the stresses.
Further dialogue between designers,
manufacturers and operators is necessary
to evaluate the impact of cyclic temperature fluctuations, which depend on the
size and configuration of the BAHE.
The Brazed Aluminum Plate Fin Heat
Exchanger Manufacturers' Association
(ALPEMA) recommends not to exceed
the rate of temperature change across any
heat exchanger pass beyond 2°C/min
or 60°C/hr, as high thermal stresses can
60

40
30
Temperature of metal wall in contact with vapor

Should BAHEs be depressurized?

50

20
40

10

30
-10
Temperature of metal wall in contact with liquid

-20

20

-30
10
Actual pressure

-40

Bulk liquid temperature

-50

0
0

300

600

900

1,200

1,500
Time, sec

1,800

2,000

2,400

2,700

FIG. 1. Effect of pressure reduction on a gas of 80 mol% methane, 10 mol% ethane,
10 mol% propane.

30

NOVEMBER/DECEMBER 2020 | GasProcessingNews.com

3,000

Pressure, barg

Temperature, °C

Bulk vapor temperature
0

damage the aluminum cores.1 If stream
temperature changes are cyclic or recurring, then the allowable rate of temperature must be less than 1°C/min to prevent thermal fatigue.
Some operators do not strictly follow
these limits during heating or cooling
operations (e.g., startup, shutdown and
emergency depressurizing). Generally,
the ALPEMA members allow up to 5°C/
min for these not-so-frequent-scenarios.
If a BAHE experiences high-temperature
changes for a longer period of time, then
the manufacturer or maintenance experts
should be consulted for inspection and
possible leak tests or maintenance.
For example, on June 27, 2016, Enterprise Products' gas plant in Pascagoula,
Mississippi saw the failure of a BAHE,
which resulted in a major loss of containment that shut down the plant for 6 mos.
This article suggests how to safely design
and operate BAHEs to avoid thermal shock
and fatigue. This will also help remove the
" black box " tag from these heat exchangers.
Two practices are mostly followed for
depressurizing of BAHE passes in case
of an emergency situation, e.g., fire and
gas detection:
1. Provide shutdown valves at the
inlet/outlet of each pass and keep
the exchanger under pressure
2. Depressurize in a controlled
manner to remove the inventory.
Some companies decide not to depressurize the BAHE and leave the liquid/
vapor inventory inside the cores in case
of emergency, including confirmed fire
and gas detection. With this approach, automatic emergency shutdown valves are
provided at the inlet and outlet of all passes
and are forced closed in case of external fire
or manual shutdown by an operator. These


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Hydrocarbon Processing - December 2020

Table of Contents for the Digital Edition of Hydrocarbon Processing - December 2020

Contents
Hydrocarbon Processing - December 2020 - Intro
Hydrocarbon Processing - December 2020 - Cover1
Hydrocarbon Processing - December 2020 - Cover2
Hydrocarbon Processing - December 2020 - Contents
Hydrocarbon Processing - December 2020 - 4
Hydrocarbon Processing - December 2020 - 5
Hydrocarbon Processing - December 2020 - 6
Hydrocarbon Processing - December 2020 - 7
Hydrocarbon Processing - December 2020 - 8
Hydrocarbon Processing - December 2020 - 9
Hydrocarbon Processing - December 2020 - 10
Hydrocarbon Processing - December 2020 - 11
Hydrocarbon Processing - December 2020 - 12
Hydrocarbon Processing - December 2020 - 13
Hydrocarbon Processing - December 2020 - 14
Hydrocarbon Processing - December 2020 - 15
Hydrocarbon Processing - December 2020 - 16
Hydrocarbon Processing - December 2020 - 17
Hydrocarbon Processing - December 2020 - 18
Hydrocarbon Processing - December 2020 - 19
Hydrocarbon Processing - December 2020 - 20
Hydrocarbon Processing - December 2020 - 21
Hydrocarbon Processing - December 2020 - 22
Hydrocarbon Processing - December 2020 - 23
Hydrocarbon Processing - December 2020 - 24
Hydrocarbon Processing - December 2020 - 25
Hydrocarbon Processing - December 2020 - 26
Hydrocarbon Processing - December 2020 - 27
Hydrocarbon Processing - December 2020 - 28
Hydrocarbon Processing - December 2020 - 29
Hydrocarbon Processing - December 2020 - 30
Hydrocarbon Processing - December 2020 - 31
Hydrocarbon Processing - December 2020 - 32
Hydrocarbon Processing - December 2020 - 33
Hydrocarbon Processing - December 2020 - 34
Hydrocarbon Processing - December 2020 - 35
Hydrocarbon Processing - December 2020 - 36
Hydrocarbon Processing - December 2020 - 37
Hydrocarbon Processing - December 2020 - 38
Hydrocarbon Processing - December 2020 - 39
Hydrocarbon Processing - December 2020 - 40
Hydrocarbon Processing - December 2020 - 41
Hydrocarbon Processing - December 2020 - 42
Hydrocarbon Processing - December 2020 - 43
Hydrocarbon Processing - December 2020 - 44
Hydrocarbon Processing - December 2020 - 45
Hydrocarbon Processing - December 2020 - 46
Hydrocarbon Processing - December 2020 - 47
Hydrocarbon Processing - December 2020 - 48
Hydrocarbon Processing - December 2020 - 49
Hydrocarbon Processing - December 2020 - 50
Hydrocarbon Processing - December 2020 - 51
Hydrocarbon Processing - December 2020 - 52
Hydrocarbon Processing - December 2020 - 53
Hydrocarbon Processing - December 2020 - 54
Hydrocarbon Processing - December 2020 - 55
Hydrocarbon Processing - December 2020 - 56
Hydrocarbon Processing - December 2020 - 57
Hydrocarbon Processing - December 2020 - 58
Hydrocarbon Processing - December 2020 - 59
Hydrocarbon Processing - December 2020 - 60
Hydrocarbon Processing - December 2020 - 61
Hydrocarbon Processing - December 2020 - 62
Hydrocarbon Processing - December 2020 - 63
Hydrocarbon Processing - December 2020 - 64
Hydrocarbon Processing - December 2020 - 65
Hydrocarbon Processing - December 2020 - 66
Hydrocarbon Processing - December 2020 - 67
Hydrocarbon Processing - December 2020 - 68
Hydrocarbon Processing - December 2020 - 69
Hydrocarbon Processing - December 2020 - 70
Hydrocarbon Processing - December 2020 - 71
Hydrocarbon Processing - December 2020 - 72
Hydrocarbon Processing - December 2020 - 73
Hydrocarbon Processing - December 2020 - 74
Hydrocarbon Processing - December 2020 - 75
Hydrocarbon Processing - December 2020 - 76
Hydrocarbon Processing - December 2020 - 77
Hydrocarbon Processing - December 2020 - 78
Hydrocarbon Processing - December 2020 - 79
Hydrocarbon Processing - December 2020 - 80
Hydrocarbon Processing - December 2020 - 80A
Hydrocarbon Processing - December 2020 - 80B
Hydrocarbon Processing - December 2020 - 81
Hydrocarbon Processing - December 2020 - 82
Hydrocarbon Processing - December 2020 - Cover3
Hydrocarbon Processing - December 2020 - Cover4
Hydrocarbon Processing - December 2020 - GP-1
Hydrocarbon Processing - December 2020 - GP-2
Hydrocarbon Processing - December 2020 - GP-3
Hydrocarbon Processing - December 2020 - GP-4
Hydrocarbon Processing - December 2020 - GP-5
Hydrocarbon Processing - December 2020 - GP-6
Hydrocarbon Processing - December 2020 - GP-7
Hydrocarbon Processing - December 2020 - GP-8
Hydrocarbon Processing - December 2020 - GP-9
Hydrocarbon Processing - December 2020 - GP-10
Hydrocarbon Processing - December 2020 - GP-11
Hydrocarbon Processing - December 2020 - GP-12
Hydrocarbon Processing - December 2020 - GP-13
Hydrocarbon Processing - December 2020 - GP-14
Hydrocarbon Processing - December 2020 - GP-15
Hydrocarbon Processing - December 2020 - GP-16
Hydrocarbon Processing - December 2020 - GP-17
Hydrocarbon Processing - December 2020 - GP-18
Hydrocarbon Processing - December 2020 - GP-19
Hydrocarbon Processing - December 2020 - GP-20
Hydrocarbon Processing - December 2020 - GP-21
Hydrocarbon Processing - December 2020 - GP-22
Hydrocarbon Processing - December 2020 - GP-23
Hydrocarbon Processing - December 2020 - GP-24
Hydrocarbon Processing - December 2020 - GP-25
Hydrocarbon Processing - December 2020 - GP-26
Hydrocarbon Processing - December 2020 - GP-27
Hydrocarbon Processing - December 2020 - GP-28
Hydrocarbon Processing - December 2020 - GP-29
Hydrocarbon Processing - December 2020 - GP-30
Hydrocarbon Processing - December 2020 - GP-31
Hydrocarbon Processing - December 2020 - GP-32
Hydrocarbon Processing - December 2020 - GP-33
Hydrocarbon Processing - December 2020 - GP-34
Hydrocarbon Processing - December 2020 - GP-35
Hydrocarbon Processing - December 2020 - GP-36
Hydrocarbon Processing - December 2020 - GP-37
Hydrocarbon Processing - December 2020 - GP-38
Hydrocarbon Processing - December 2020 - GP-39
Hydrocarbon Processing - December 2020 - GP-40
Hydrocarbon Processing - December 2020 - GP-41
Hydrocarbon Processing - December 2020 - GP-42
Hydrocarbon Processing - December 2020 - GP-43
Hydrocarbon Processing - December 2020 - GP-44
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