Plastic Pipe Facts™

E.I. DuPont de Nemours, Two Texas CPI Plants:

In 2000 and 2002, two DuPont chemical plants suffered HDPE fused flange failures that resulted in costly repairs and, in one case, severe production losses. The failures occurred after 33 and approximately 55 months of service, respectively.1

In the first case, a fused 36" HDPE (PE 3408) fused flange used in a cooling water supply line (60 psi operating) failed at the junction of the flange and the fused-on stub-end, creating a sinkhole. The subsequent investigation found a number of issues:

    1. Several of the 24” fabricated flanges were previously rejected as a result of not meeting manufacturer’s quality acceptance criteria.
    2. Several lengths of pipe bulged "excessively" during the pressure test and were found to be below the minimum required wall thickness.
    3. The melt-flow of the failed 36" flange was 45% higher than that of the stub-end, creating the suspicion that high variability in melt flow might interfere with fusion integrity, but not a definitive cause for failure.
    4. SEM fractography indicated brittle fracture around the fracture zone.
    5. Oxidation Induction Times (OIT) were highly variable, with the fabricated flange having lower OIT's than the pipe itself; thermal degradation (insufficient anti-oxidant package) was "very likely" on the flange which could have resulted in a weak weld.
TX1
"Polyethylene Fabricated Flange Failures" 2003, S. Whitlow; NACE International.

 

In the second case, a water return line operating at 77 psi experienced a failure in a 36" fabricated fused-on HDPE (PE 3408) flange after about 55 months of service. As a result of the failure, the plant production capacity was halved with "major" business impact. The investigation found:

  1. During project installation, two fusion joints on a branch connection failed requiring replacement.
  2. The failed fusion joint (90% of circumference) exhibited little bonding except at the outer edge – indicating a "cold weld" or poor fusion as the cause of the failure.
TX1
"Polyethylene Fabricated Flange Failures" 2003, S. Whitlow; NACE International.

 

  1. "Polyethylene Fabricated Flange Fitting Failures", S. Whitlow, NACE International 2003.