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Supervision of general overhaul of well control equipment

During the period from 12 March to 20 May 2003, the Norwegian Petroleum Directorate has conducted audits of Transocean, Cameron, Subsea Services and DnV-Stavanger. The audit activities were aimed at the respective company's management and implementation of general overhaul of well control equipment on the Transocean Searcher.


Transocean Searcher

Transocean Searcher

Background for the audit

The audit activity is a continuation of an activity in 2002 and a follow-up of the industry's transfer of experience and measures after other audits aimed at general overhaul of well control equipment a few years back.

The NPD has had somewhat mixed experiences from previous audits of a similar nature. There have been cases where the supplier's recommendations and specifications have not been followed by the shipowner. Third-party verifications of BOP equipment have been deficient, in part based on insufficient information concerning the suppliers' tolerance specifications, welding procedures, etc.

Over the past ten years, mobile drilling rigs have largely been used to conduct production drilling and completion. The experience gained can indicate that BOPs are now far more exposed to aggressive well fluids, which leads to extensive corrosion on seal faces and components.

This has led to extra wear and tear which is often not discovered until a general overhaul is conducted. In addition, the requirements for use of more environmentally-friendly additives in the control fluid have resulted in substantial challenges.

Because of the new additives' poorer inhibiting effects, this can lead to undesirable corrosion and increased growth of bacteria inside the control system, accompanied by more frequent faults.

Experiences from the industry related to previous general overhauls and extension of the general overhaul intervals may signal a potential need for the NPD to tighten requirements for the industry's quality assurance and control of the general overhaul and maintenance program.

Viewed in light of the BOP's key importance in handling well kick situations and preventing potential ensuing explosions or other serious accidents, the NPD has chosen to emphasize the player's systematic general overhaul programs in order to ensure the quality and accessibility of the equipment.

The audit activity was carried out vis-à-vis the mobile drilling rig Transocean Searcher, which is on a long-term contract for Statoil on Åsgard.

Trancoean Searcher has a system whereby SPS is divided into intervals rather than gathering everything together, which was the case previously. Several shipping companies in the sector use this method. In addition, the rig and the BOP are scheduled for general overhaul/SPS in the spring of 2003. The NPD wanted to verify the following:

· that maintenance recommendations are followed up

· how the suppliers' recommended upgrades are handled by the shipowner

· handling of condition reports

· the role of the verification company in inspection and preparation of the condition report

· that previous overhauls have been carried out in accordance with requirements

· that historical information from BOP overhauls is collected and used systematically

· that the most recent overhaul is verified according to requirements

· that the BOP has been function-tested in accordance with requirements

· whether components that are used are produced in accordance with acceptable standards.

Purpose of the audit

1. The NPD wants to contribute to maintaining and further developing the reliability of BOPs. Ref. Preventor's report on safety on the shelf, in which blowouts are considered to be the largest single contributing factor to the risk of major accidents.

2. Contribute to ensure that the players follow up the preconditions for regulatory reform as regards changing the frequency of general BOP overhauls from every four years to every five years.

3. Verify that normative industry standards are followed when critical components are replaced.

Result of the audit

The NPD has the impression that the understanding that Transocean, DnV, Cameron and Subsea Services have regarding the requirements for management and implementation of general overhauls of well control equipment are in concurrence with the applicable regulatory requirements.

Based on the audit activity, it is the NPD's impression that Transocean ensures safety in the management of both technical and operational aspects associated with the planning and execution of activities related to the general overhaul of BOPs.

The NPD notes that there are some outstanding items from Transocean's own audit of Subsea Services that have not yet been closed.

The NPD has no further comments on these items as they are being followed up by Transocean.

It is the NPD's impression that the technical condition of the BOP is safeguarded through the maintenance system on the rig. Transocean's methodology for general overhaul of the BOP in various periods with a complete assembly test every fifth year which covers pressure testing of valves and function testing of the entire BOP control system with associated components/equipment, is regarded as being in accordance with regulatory requirements.

The assessment of condition conducted offshore to determine the scope of work for the general overhaul is regarded as being an important part of the methodology applied.

There is a need to clarify temperature restrictions for use of the Regan Diverter.

The NPD is of the opinion that the audit activity confirms that the industry has implemented and continues to implement the necessary transfer of experience and quality enhancement of planning, follow-up and implementation in connection with general overhaul of BOPs in relation to previous, similar audits conducted by the NPD.