In this series, our head of Rig Inspection Services Steven Lee shares tips on how operators and owners can get through rig inspections with flying colours – and which pitfalls to avoid! Mr Lee has more than a hundred rig inspections under his belt, from all parts of the world. In this chapter we are talking about the importance of Drilling Control Systems.
Advanced Drilling Control Systems have been in operation for a number of years, with proven technology implemented and used worldwide. Although numerous hull and drilling packages have been delivered with the same turnkey design, individual implementations and construction approaches can make each drilling unit control system very unique.
One of the first things that any good control systems inspector will review is the alarm history and the network infrastructure status. Any repeated or inhibited alarms will be homed in on and queried with the crew, as will any network infrastructure issues. These can point other members of the inspection team to potential physical issues or operational problems.
As with most other aspects of surviving a rig inspection, preparation by the rig inspection team, the rig management and crew is key. A good rig inspection team will always review the manuals for the specific system being inspected to ensure that systems are operating as intended by the original equipment manufacturer (OEM).
Visual inspection and documentation review alone will fail to reveal any number of operational and potentially safety-critical faults. The only way to ensure that systems are operating as intended is to conduct proper functional testing to simulate all potential operating scenarios. This could take the form of pipe handling exercises, mud circulation tests, anti-collision system testing, etc.
An example of this was during an acceptance inspection when mud pump auxiliary shutdowns were tested on a 6th generation drillship which had been delivered nine years previously. The particular unit had four mud pumps and there were four auxiliary shutdowns to be tested, so it was agreed, since the unit had been in operation for so long, to perform only a random sample of the shutdowns – one different shutdown per mud pump. It quickly became apparent, however, that the loss of blower motor shutdown did not activate on the mud pump it was tested on as expected based on the manual.
The logical approach was to then test the same shutdown on the three other mud pumps, which then returned an intriguing result – the shutdown only operated on two out of the four mud pumps! Further investigation by the crew with the assistance of the OEM, revealed that the software versions in the PLCs controlling the mud pumps had been inconsistent since delivery, which caused the mismatch in shutdown logic.
This was an excellent lesson to show that nothing can be taken for granted, no matter how long a unit has been in operation for and the benefits in taking the time to understand how the equipment is supposed to function in different scenarios.
Another example was in testing the anti-collision system of a jack-up that had been delivered eight years prior and had an established track record in the Southern North Sea in the UK, Dutch and Danish sectors. It was discovered through systematic testing of all potential collision scenarios that it was possible for the iron roughneck to strike the catwalk machine and was not prevented by the system. The rig crew then reverted to the OEM to investigate and install a software patch. In this case, although the documentation stated that all potential equipment collisions were accounted for in the anti-collision system, thorough testing found an issue that had never been identified.
These examples prove that nothing in rig inspection, especially drilling control systems, can be taken for granted. Proper functional testing carried out in a controlled situation is a much more preferable time to find a potentially dangerous system flaw, instead of while drilling into the reservoir. Which would you rather?