ADC has been tasked to provide a Tubular Handling Assessments for various rigs in order to ensure that equipment was fit for purpose and identify any single-point human barriers present within the drilling system that could result in dropped tubulars, dynamic dropped objects or equipment damage.
During the periods that the ADC teams were on-board, the rigs have conducted various drilling operations and ADC has witnessed all aspects of onboard tubular handling.
ADC conducted a review of all procedures identified within the Tubular Handling process and a physical inspection of all of the equipment utilised within the process. Operations were witnessed to determine if the equipment was being operated as per the Functional Design Specifications, Operating Instructions and work instructions.
The Fingerboard consisted of a set of steel fingers dividing the rows of tubular stands. Each finger (row) was equipped with a number of mechanical locking latches which were closed by a mechanical spring and opened by air pressure through pneumatically operated cylinders. The pneumatic latches were described to be of a failsafe design such that if air pressure loss occurred, each of the individual latches would go into locked down position.
Air Pressure must be applied to the pneumatic cylinders to open the latches as required. A valve cabinet located near the fingerboard contained the control valves that directed compressed air from the control valve to the latch cylinders via pneumatic piping hoses.
The control valves within the valve cabinet also sent signals to control system that provided feedback information to the driller that the solenoid was activated and on the drillers screen the finger appeared as a latch open indication.
The fact that the pneumatic solenoid was activated and indicated did not confirm that the finger was actually open. IADC Alert 15-10 Fatality on Drill Floor described an accident where a tubular was caught in a fingerboard latch and the pipe racking system (PRS) was retracted. As the PRS retracted, the tubular was bent and stored energy was released as the tubular was pulled from the lower racking arm gripper. The lower end of the tubular was catapulted back across the drill floor killing one of the rig crew.
This issue is well understood and most rigs use a system of visual back up or CCTV system to confirm that the latches are open prior to moving tubulars in or out of the fingerboard. However, ADC have identified on more than one occasion that from the roughneck’s position outside of the Red zone, it was not possible to see the position of the latches within certain areas of the fingerboards and that lip service was being paid to these checks.
Crew need to fully understand their responsibility to confirm that latches are open prior to moving tubulars and to fully understand the potential implications if latches remain closed.
The Drillers chair Dolly Retract (Left switch) and Elevator links tilt (Right switch) were virtually identical tactile buttons placed next to each other on the right joystick. Both were controlled by a thumb roll forward or back. It was considered to be very easy to inadvertently press the left switch whilst intending to press the right. Regardless of whether the Dolly was selected in Auto or Manual Mode, the Stick top switch was always active.
In Auto mode the Dolly fully retracted upon activation of the switch. In Manual Mode the Dolly retracted only as long as the button was activated.
The lack of an appropriate interlock to prevent inadvertent dolly retraction with tubular connected to the Top drive or elevators was considered to be a major design flaw in the system because inadvertent dolly retraction could result in a bent drill pipe, damage to the rotary table and damage to the top drive.
A suitable modification was required to prevent accidental dolly retraction. Meanwhile, in order to reduce the consequences of an inadvertent selection of this switch, ADC suggested that the dolly should only be operated in manual mode. Thus, if the button was inadvertently activated, the operator would be more likely to identify the movement and cease the operation before the dolly had moved any significant distance.
E: Email ADC UK
