Journal of Failure Analysis and Prevention

, Volume 12, Issue 1, pp 30–36 | Cite as

Analysis of a Failure in a Polyethylene Gas Pipe Caused by Squeeze off Resulting in an Explosion

Case History---Peer-Reviewed

Abstract

A failure caused by squeezing off a polyethylene (PE) gas pipe was investigated. The failure mechanisms were analyzed. Two modes of fracture were found: brittle and slow crack growth (SCG). The formation of the brittle fracture was particularly interesting because its origin was not produced by a defect in the material, but by the compressive stress fields produced by squeezing and enhanced by the visco-elastic behavior of PE. The micro deformation, which was associated with the nucleation of brittle fracture, was analyzed. The time for the SCG was predicted based on the size of the brittle fracture. It is most likely that the failure would not have occurred if the squeeze and release rates had been controlled.

Keywords

Pipe failure Brittle fracture Slow crack growth Micro-deformation Polymer 

List of Symbols

e

Strain

t

Thickness of pipe wall (Eq 1)

g

Gap = minimum distance between squeeze rods (Eq 1)

t

Lifetime (Eq 2)

A

Measure of the property of a resin that resists slow crack growth

K

Stress intensity

Y

Geometric factor contained in the definition of K

S

Stress

a

Size of notch

t12

Lifetime at 12°C

S12

Stress at 12°C

d

Diameter of squeeze rods

X

Distance along BE in Fig. 2. X = 0 at point B

G

Distance between squeeze rods as a function of X (Eq 4)

go

Minimum distance between squeeze rods

eo

Maximum squeeze strain

e

Strain as a function of X (Eq 4)

ts and tp

Lifetimes in squeezed and not squeezed pipe

as
Effective length of notch in failed pipe based on area of brittle fracture (Fig. 1)
Fig. 1

SEM of the fractured area. Part of the boundary between the brittle and SCG areas is delineated

ap

Size of typical defect in gas pipes = 0.14 mm

ρ

Radius of curvature of bent pipe wall (Fig. 5)

δ

ρ − t/2

Notes

Acknowledgment

Routine legal procedures during the investigation of the explosion provided critical information about the technical factors involved.

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Copyright information

© ASM International 2011

Authors and Affiliations

  1. 1.Department of Material Science and EngineeringUniversity of PennsylvaniaPhiladelphiaUSA
  2. 2.FAI Materials Testing Laboratory Inc.MariettaUSA

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