The BOP storage stump on the side of the cantilever beam on an older cantilever jackup does not easily allow for offline stump testing of the BOP stack. Vertical access to the top of the stack is limited and does not allow for a test mandrel to screw into the test stump. Currently, short test mandrels with shoulders that locate beneath the rams are utilized for all sizes except for 9â…" casing rams. Comments on the following issues would be appreciated.
a) Do most jackups routinely stump test prior to N/U on wellhead? Newer generation vs older generation rigs?
b) Common practices for stump testing on cantilever jackups.
c) Use of test mandrels with shoulders which locate beneath the ram to prevent pumping out (as opposed to test mandrels which screw into the test stump). Can they damage the rams? Can they be used on annular preventers?
d) Any incidents with stump testing: launched test joints, damage to BOPs, injuries, etc.
e) Should stump test date start the interval until the next test or should it start when the stump tested BOPs are installed.
f) Do contracts usually require the drilling contractor to stump test BOP prior to installation?
Usually, to save time, all BOP components (PR, BSR, Annular BP, CL & KL, choke M, ...) are P/tested on a stump (while drilling a surface hole for instance).
After N/up the stack on a wellhead, all BOP components are function tested and a WH connection P/T is performed using either PR or Annular BP.
In order to repeat the BOP P/T after 14 or 21 days (frequency), is there any API RP whether to start counting from P/T on the stump or on the wellhead?Thanks
ONE: Please find below a description of a "near-hit" incident on the drilling unit "Hunter" which is under contract on location 3/7-4.
The incident happened while pressure testing the 15.000 psi BOP stack in situ on the test stump.
Date of incident: 23rd September 1989 Time of incident: 01.30 hours
Injury/damage: no injury, damage sustained involved cable tray, one test joint, BOP rams, perspex corrugated roofing and insert bushing.
Events leading to the incident:While the drilling unit was in the harbour, Contractor changed their previous 10.000 psi BOP stack for a new 15.000 psi BOP stack.
The rig departed on 16th September 1989 with a number of outstanding work items to be completed on the stack including detailed testing of the rams and annular preventers. Preparations for testing were made on 22nd September. A permit to work was issued, warning signs were placed in strategic places and personnel informed. Testing was to be carried out deploying the test stump, which contains a replaceable insert bushing with a 4 1/2" IF box connection. The test stump is a Vetco design with a Vetco H/4 profile.
Replacement of this bushing is done by means of so called "jay" mechanism, which on the top forms a seal by means of an "O" ring placed between the shoulder of the bushing and the tool-joint shoulder of the test joint.
The test joint was a 5" HWDP with the wear knot machined down to 5" OD and a plug welded in place in the bottom of the tool-joint pin. The test joint, already installed by the sub sea engineer on 19th September, had been lowered through the BOP and screwed tight into the insert bushing with a chain tong. The lower pipe rams were closed and testing commenced.
The incident: After a satisfactory low initial pressure test of 500 psi, the pressure was slowly increased to 15.000 psi with the test pump. Without any warning the test joint was ejected at high speed from the top of the BOP through the hatch in the perspex roofing of the BOP test area.
The joint subsequently descended again and penetrated the roof leaving a hole and landed in the electric cable tray which supplies power to the BOP handling cranes. These were bent out of shape but nobody was injured.
Initial investigations revealed the following: The test joint was ejected with such a force that the tool-joint parted from the pipe body leaving the tool-joint, screwed to the insert bushing, on the top of the test stump. The jay upsets on the insert bushing had also sheared off by the force.
The welded plug in the bottom of the test joint was found to be protruding 2 to 3 mm below the crest of the pin end of the tool joint.
This is believed to be one of the causes of the incident, as this prevented the tool joint shoulder from forming a pressure tight seal as the welded plug bottomed out prior to make up thereby allowing the test pressure to act directly upon the cross sectional area of the welded plug and creating a full differential across this area. Shell personnel were not made aware of the pipe being blanked off. The force of the tool joint hitting the bottom of the lower pipe rams caused belling at the outer edges of the rams. These had to be ground down prior to opening the bonnets for inspection.
Follow-up investigation - findings - recommendations: The test joint was replaced with a through bore joint and the BOP repaired and successfully pressure tested.
The authorities were informed and have been requested to issue an industry alert.
A full investigation involving the drilling contractor & vendors has since been carried out and revealed the following:
The previous BOP stack had a different connector and the drilling contractor claimed that testing with a blanked off joint was a Vendor recommended procedure.
Operator investigated this with Vendor, and their procedure clearly states to use an open test joint or a specially designed test button which is placed below the ram to be tested.
The Vetco test procedure also clearly states the requirement of testing with a through bore joint.In addition, the Vetco test stump has a connection in the centre of the stump leading to atmospheric pressure but this line was found to be blind plugged.
Had this line been open then any pressure leaking past the seal or threads would have leaked off without any harm.
It has been recommended that before any pressure testing is to take place a check is made that the test joint is not plugged off and is free from any internal obstructions.
The drilling contractor has changed the testing procedure accordingly and relevant changes have been made to the safety and QA manuals.
The extreme potential for injury was discussed in detail at all levels on this rig and the base.TWO: Incident occurred on a platform whilst pressure testing the 13â…" stack on the stump. The special test joint became detached from the test stump, moved up some 4 ft. Where it was stopped against the drawworks sump. The testjoint was blanked off.