Pressure Testing Incident at Expo Group 2003

Please review the attached incident investigation report relating to an incident that occurred in a workshop when pressure testing was being carried out on a 5K choke manifold TX 54-10.
Please review pressure testing practices on your rig to ensure this risk is appropriately managed.

• Pressure testing 5K choke manifold TX 54-10
• Choke tested inside GY base well test pressure test bay
• Workshop Foreman and Technician inside test bay to inspect for leaks
• Thermowell 3/4″ NPT failed (The thermowell is about 9 ins long and weighs approx 1 kg.)
• Hit Workshop Technician on his knee from approx 0.5 meters, resulting in serious injury.

Severe corrosion had affected the mechanical integrity of the female thread.
The forces generated by the 5000 psi test pressure overcame the mechanical strength of the corroded thread and caused the thermowell to be ejected.

Procedural Failure

Pressure retaining threads and tappings should have been inspected for wear and corrosion during the maintenance of the choke manifold.
See the photographs and answer the question, had they been?
Calibrated thread gauges are to be used for checking the condition of the threads. The gauges were specified in the procedures but had not been used.
A review of the risk assessment for pressure testing had not been conducted prior to starting the test.
Two maintenance technicians entered the test bay to investigate leaks from the choke manifold assembly. It was not known if the pressure
had stabilized prior to the technicians entering the bay. Actual pressure on the assembly was not known/recorded.

Procedural ineffectiveness

The procedures were found to be outdated with several cross-references to memos, some 5 years old.
Pressure tests had not been recorded on charts, although calibrated gauges were routinely used.
Job cards were not being completed as the maintenance work was progressed.
The technician was working under the supervision of the workshop foreman during the re-build and testing of the choke manifold.

Facilities

The test bays were built to contain the failure of equipment during pressure testing. However, the bay walls and doors were not fitted with viewing ports or any other means to identify the source of leaks.
Normal practice was to apply the test pressure and wait for pressure stabilization before entering the test bay to visually inspect for leaks.

Calculations

Pressure = Stored Energy
When pressure acts upon an area, a force is generated Pressure is measured in Pounds per Square Inch (psi)
1 psi = 0.0689 bar
1 psi = 6.895 kPa

The higher the pressure (ie 10,000psi) or The larger the area (ie 400 barrel tank) = The Greater the Force

Calculating the force acting upon the thermowell
Force = Pressure x Area
Test pressure = 5000 psi
Affected area = 0.785 sq ins
Force = 1 314 tons

When the NPT thread failed the stored energy was released and propelled the thermowell at a velocity of 42 meters/ sec = 94 MPH

1. Disseminate and roll out the investigation findings to workshop and operations staff involved in maintenance and pressure testing activities.
   Action: Region Manager(s)
2. Perform an audit of all the actions arising from this incident to verify that they are effective and have been consistently applied throughout
   the Region.
   Action: Region HSEQC Manager
3. Review and revise the procedures for the maintenance and inspection of pressure retaining equipment (particularly threads and threaded
   fittings). Revise the pressure testing procedures for all equipment.
   Action: Region Technical Manager/SES BS
4. Train staff in the application of these new procedures and ensure that the training is recorded.
   Action: Region Manager(s)
5. Review and report upon the Region’s pressure testing facilities against industry best practice with a view to implementing best practice.
   Action: Region Technical Manager
6. Dismantle and inspect ALL pressure retaining threads on Yarmouth Base equipment using calibrated thread gauges. Ensure condition of
   threads are established and deficient components are scrapped and replaced as required prior to any further pressure testing activity.
7. Investigate alternative materials and options for pressure retaining threads for Expro owned equipment with a view to adopting same.
   Action: Region Technical Manager/SES BS Issue an alert to all Expro bases and clients upon completion of the investigation (Interim alert already issued).
   Action: Region HSEQC Manager
8. Issue an alert to all Expro bases and clients upon completion of the investigation (Interim alert already issued).
   Action: Region HSEQC Manager