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.
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Abbreviations
- 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
- t 12 :
-
Lifetime at 12°C
- S 12 :
-
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)
- g o :
-
Minimum distance between squeeze rods
- e o :
-
Maximum squeeze strain
- e :
-
Strain as a function of X (Eq 4)
- t s and t p :
-
Lifetimes in squeezed and not squeezed pipe
- a s :
-
Effective length of notch in failed pipe based on area of brittle fracture (Fig. 1)
- a p :
-
Size of typical defect in gas pipes = 0.14 mm
- ρ:
-
Radius of curvature of bent pipe wall (Fig. 5)
- δ:
-
ρ − t/2
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Acknowledgment
Routine legal procedures during the investigation of the explosion provided critical information about the technical factors involved.
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Brown, N., Crate, J.M. Analysis of a Failure in a Polyethylene Gas Pipe Caused by Squeeze off Resulting in an Explosion. J Fail. Anal. and Preven. 12, 30–36 (2012). https://doi.org/10.1007/s11668-011-9527-z
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DOI: https://doi.org/10.1007/s11668-011-9527-z