Hydrocarbon Processing - December 2020 - 73
Maintenance
and Reliability
A. K. DATTA, Process Consultant, Brisbane, Australia
High-frequency acoustic excitation-Part 1
Failure of a piping section at the outlet of pressure safety
valves (PSVs) and control valves-where significant differential pressure exists (particularly in gas processing industries)-is a common problem in industries. Most failures are
caused by acoustic-induced vibration. High-pressure discontinuity generates high vibration and sound levels, causing the
failure of the piping system. Generally, the likelihood of failure
(LOF) is established through the calculation of sound power
level (represented as PWL) at the source and at different sections of the downstream piping. Normally, it is the welded
joint that fails due to acoustic excitation. The welded joint
can be of any type, including a branch connection, welded tee,
welded support, etc.
Background. While several modes of acoustic-induced vibration failure exist, this article is restricted to the following
types of flow regime and process connections:
* Flow regime, only gas phase
* Downstream of pressure safety valve
* Blowdown lines, downstream of restriction orifice
* Downstream of control valve
* High-pressure venting.
For control valves, sometimes low noise trim is fitted to
avoid the generation of excessive noise. In such cases, the possible reduction of noise level due to trim will be obtained from
the valve manufacturer.
High-frequency acoustic excitation.1 In a gas system,
high-frequency acoustic energy can be generated by a pressure-reducing device, such as relief valve, blowdown valve,
control valve, etc. Acoustic fatigue is of particular concern, as
it tends to affect the safety related system.
The time to failure is short (typically a few minutes or
hours) due to the high-frequency response. In addition to giving rise to high tonal noise levels external to the pipe, this form
of excitation can generate severe high-frequency vibration of
the pipe wall. The vibration takes the form of local pipe wall
flexure (the shell flexural mode of vibration), resulting in potential high dynamic stress levels at circumferential discontinuities on the pipe wall, such as small-bore connections, fabricated tees or welded pipe supports.
The high noise levels are generated by high-velocity fluid impingement on the pipe wall, turbulent mixing and, for
choked flow, shockwaves downstream of the flow restriction.
They are a function of pressure drop across the pressurereducing device and the gas mass flowrate.
Typical dominant frequencies associated with high-frequency acoustic excitation are between 500 Hz and 2,000 Hz.
PROCEDURE
The failure possibility is established through the calculation
of likelihood of failure (LOF). It is at the discontinuities with
an LOF equal to one where corrective action is required. The
following parameters are estimated for overall calculation of
LOF number for various scenarios.
Mach number, downstream piping.2 The Mach number of
the downstream fluid is calculated using Eq. 1:
Mach = 3.23 105
ZT 0.5
W
2
Din 2 MW
P2
1,000
(1)
PWL design limit.3 The design limit of sound power level is
calculated with Eq. 2:
PWLD = 173.6 0.125
Din
t
(2)
If the design limit exceeds the sound power level at any point
of the pipeline, the pipeline design is adequate.
Sound power level at source.1 The sound power level at
source is calculated using Eq. 3:
P P
PWLS = 10log 1 2
P1
3.6
2
1.2
W
T1
+
MW
3,600
126.1 + K NLT
where:
Mach
W
P1
P2
Din
Z
T1
=
=
=
=
=
=
=
(3)
Mach number
Gas flowrate, kg/hr
Upstream pressure, kPa
Downstream pressure, kPa
Pipe inside diameter, mm
Downstream gas compressibility
Upstream temperature, K
Hydrocarbon Processing | DECEMBER 2020
73
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
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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
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Hydrocarbon Processing - December 2020 - 29
Hydrocarbon Processing - December 2020 - 30
Hydrocarbon Processing - December 2020 - 31
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Hydrocarbon Processing - December 2020 - 33
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Hydrocarbon Processing - December 2020 - 35
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Hydrocarbon Processing - December 2020 - 40
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Hydrocarbon Processing - December 2020 - 42
Hydrocarbon Processing - December 2020 - 43
Hydrocarbon Processing - December 2020 - 44
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Hydrocarbon Processing - December 2020 - 51
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Hydrocarbon Processing - December 2020 - 54
Hydrocarbon Processing - December 2020 - 55
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Hydrocarbon Processing - December 2020 - 60
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Hydrocarbon Processing - December 2020 - 63
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Hydrocarbon Processing - December 2020 - 67
Hydrocarbon Processing - December 2020 - 68
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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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