Instrument tubing failure resulting in a serious injury

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On May 1 2011, during commissioning of a high pressure gas well in Canada, an operator identified a small leak in newly installed small bore tubing that connected the wellhead to a meter skit. He obtained wrenches and attempted to tighten the connection. As he commenced the task with the tubing containing full well bore pressure, the tubing parted and the operator was blasted in the face by the released high pressure gas. The gas caused a 4 ½” tear in his esophagus, deflated one lung and partly deflated the other.

Description of Incident

Operations was commissioning a high pressure gas well (approx 3000 psi). Contractors had installed instrument tubing from the wellhead to the pre-fabricated meter skid. All tubing in the skid was to have been checked for correct installation and marked with an “x”. Three days later while flowing the well, an operator noticed that a ½” to 3/8” inch tubing fitting was leaking at the point where it was installed into a “T”’. This fitting and tubing carried full well pressure to a transmitter. The operator went to his truck and returned with two wrenches. The operator bent over the knee high fitting at about a 30 degree angle. As he placed his 11/16th wrench on the fitting nut, the tubing gas was released from the nut and the operator was blasted in the face with the full force of the gas pressure. The gas caused a 4 ½” tear in his esophagus, deflated one lung and partly deflated the other. He was transported by air to hospital where he is recovering.

The scene of tubing failure connections at the high pressure gas wellhead.

What Caused It

  • The tubing was 3/8” .049 wall thickness stainless steel. The fitting is a double ferrule style. All met manufacturer’s specs.
  • The tubing had been installed into the fitting nut to the correct depth and the ferrules were installed in the correct order.
  • The fitting nut had not been tightened as per manufacturer’s recommendations (finger tight plus 1 ¼ turns) therefore the ferrules were not “set” into the tubing. When examined post event, the nut was found to be finger tight (3 full turns).
  • The installer had ‘batch marked’ the fittings in his post installation check vs. checking then marking one at a time.
  • The well commissioning process had not caught the leaks.
  • Fittings under pressure need to be depressured before tightening; this practice may have not always be followed.

Corrective Actions

  • Leaking tubing fittings under pressure can be extremely dangerous and must be depressurized before being touched.
  • Field correcting of tubing installation deficiencies without follow up with the contractor prevents the sharing of findings and the opportunity for the contractor to correct the deficiencies and implement the necessary corrective actions into their procedures.
  • Field installed tubing should be hydrostatically or pneumatically tested per ASME B31.3 methods in conjunction with the contractor’s QA/QC program.
  • Review well commissioning processes to identify tubing installation testing and verification.
  • Verify training for the correct installation and operation of fittings.

References

  • Safety alert, ISSUE #: 10-2011, the Safety Association for Canada's Upstream Oil and Gas Industry.


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