Hydrocarbon Processing - December 2020 - 77

Maintenance and Reliability
dext
= Branch pipe external diameter, mm
FLM1 = Correction factor due to branch connection
N2
= Number of cycles to failure after applying
branch connection correction factor
FLM2 = Correction factor due to fittings
N3
= Number of cycles to failure after fitting
correction factor
FLM3 = Correction factor due to piping material
N
= Design number of cycles to failure
Lf
= Failure factor
LOF = Likelihood of failure.

A detailed calculation approach and analysis of more complex problems will be discussed in Part 2 of this article, which
will appear in the January 2021 issue.

Likelihood of failure. Once the design number of cycles to

failure is known, the failure factor is calculated using Eq. 36:
Lf = -0.1303 ln(N) + 3.1

LITERATURE CITED
Energy Institute, Guidelines for the avoidance of vibration induced fatigue failure in
process pipework, 2nd Ed., Energy Institute, London, U.K., 2008.
2
API Standard 521, " Pressure-relieving and depressuring systems, " 5th Ed.,
American Petroleum Institute, Washington, D.C., 2007.
3
NORSOK Standard L-002, Piping system layout, design and structural analysis, 3rd
Ed., Standards Norway, Norway, 2009.
4
API Standard 520, Sizing, selection and installation of pressure-relieving devices in
refineries-Part 1: Sizing and selection, 8th Ed., American Petroleum Institute,
Washington, D.C., 2008.
5
Crane Technical Paper No. 410, " Flow of fluids through valves, fittings and pipe, "
Metric Edition-SI Unit, 1986.
6
Datta, A., Process Engineering and Design Using Visual Basic, 2nd Ed., CRC Press,
New York, 2014.
1

(36)

The design value of failure factor is calculated using Eqs. 37
and 38:
If Lf < = 0.0 then Lf = 0
(37)
If Lf > = 1.0 then Lf = 1
(38)
Once the value of Lf is known, the likelihood of failure is calculated using Eqs. 40 and 41:
If Lf >= 0.5, LOF = Lf
(40)
If Lf < 0.5, LOF = 0.29

(41)

ARUN K. DATTA has been working as a consulting engineer
in the oil and gas, refining and fine chemical industries
for more than 30 yr in the field of process engineering and
design. He has served as a consultant for many process
engineering organizations in India and Australia. His
experience includes heat and mass transfer, process
simulation, exchanger design, pressure vessel design, design
of safety systems, design of control systems, etc. Mr. Datta is a chartered
Professional Engineer and an active member with the Institute of Engineers
in Australia. Apart from publishing and presenting numerous papers, he has
authored a book, Process Engineering and Design Using Visual Basic, published
by CRC Press. Mr. Datta holds a BTech degree in food technology and biochemical engineering from Jadavpur University, India, and an MTech degree
in chemical engineering from Indian Institute of Technology, Delhi, India.

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