Technical Briefs

Failure Mode Analysis of Mobile Equipment Hydraulic Leaks

[+] Author and Article Information
Mahmoud I. Awad

Department of Industrial Engineering,  ALHOSN University, Abu Dhabi 38772, UAE

Ali A. Alkelani

BMW Manufacturing Co., 1400 Hwy 101 South, Greer, SC 29651

J. Pressure Vessel Technol 134(3), 034502 (May 18, 2012) (6 pages) doi:10.1115/1.4006342 History: Received March 02, 2010; Revised March 03, 2012; Published May 17, 2012; Online May 18, 2012

Leaks in general and hydraulic leaks in specific are one of the major failure modes for mobile equipment. In-plant leak rates may range from 1% to 25%, while field leaks may range from 1% to 13% depending on the complexity of the system, assembly process, and parts quality. In this paper, the main potential leak causes are discussed and the performance of different types of fittings is compared, including JIC 37 flare fittings, O-ring boss seal, and O-ring face seal. Several potential improvement actions related to assembly process, torque specifications, and quality of manufactured fittings are proposed to reduce leaks. Among the many benefits leak reduction will result in improved customer safety and satisfaction, assembly down time reduction, cost and warranty reduction, and environmental impact reduction.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 15

Leaks by root cause: (1) loose joints, (2) pinched o-ring, (3) missing o-ring, (4) replace part, (5) disassemble and assemble, (6) unknown, and (7) internal leaks

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Figure 16

Leak rates by fitting type

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Figure 14

Process capability example: (a) groove depth and (b) O-ring cross-sectional diameter

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Figure 13

Trapezoidal O-ring

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Figure 12

ORFS torque sweep test

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Figure 11

p-chart example for hydraulic leaks

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Figure 10

Mean torque and standard deviation collected from camover tool

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Figure 9

Mean torque and standard deviation collected from a click tool

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Figure 8

Paint marking of flare fitting connection

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Figure 7

Flare fitting tightened to 14 Nm (left) and to 20 Nm (right)

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Figure 6

Flare fitting tightened to high torque level

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Figure 5

Preventing line twisting by using an alignment fixture and line clip

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Figure 4

Using fixture to assemble a joint with flare fitting

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Figure 3

Fitting with two different types of lubrication to reduce line twisting

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Figure 2

Supplier quality defects (a) cracked through the full length, (b) run out of the tee portion, (c) cracked through the internal surface of the flange, and (d) machining witness marks

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Figure 1

Types of fittings: (a) JIC 37 FF, (b) ORBS, and (c) ORFS



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