The development of the guideline – DNV RP-F116: Integrity management of submarine pipeline systems – means that the integrity of a subsea pipeline can be managed with a unified and reliable reference for both authorities and the industry. Companies will be able to use their adherence to it as part of documenting their compliance with regulations. For authorities, it provides a useful tool when reviewing or defining their regulatory regime.

A joint industry effort

The recommended practice (RP) was developed as a Joint Industry Project (JIP), with DNV, CNOOC, DONG Energy, ENI Group, Gassco, GDF Suez, Norske Shell, SINTEF, and Statoil participating. The JIP started developing RP-F116 in 2007 and the final document, released in October 2009, provides guidance on how to establish, implement and maintain an integrity-management system (IMS).

The document’s main focus is the integrity management process (IMP), which is the combined process of threat identification, risk assessment, planning, monitoring, inspection, and repair.

The IMS

In order to ensure the safe operation of its pipeline system, it is required that an operator establishes, implements, and maintains an IMS within its own organisation. The IMS consists of an IMP supported by a number of elements.

The IMP consists of the following steps:

• 1. Integrity management planning including threat identification and assessments of associated risks. This activity provides long and short-term (annual) plans;
• 2. Performance of inspection, monitoring, and testing activities;
• 3. Integrity assessment based on inspection and monitoring results, and other relevant historical information; and,
• 4. Mitigation, intervention and repairs activities.

Each of these steps, on which RP-F116 provides guidance, needs to be planned in detail, executed, and documented.

Prior to a pipeline being put into service, an integrity philosophy should be developed, taking into consideration the pipeline design and how the integrity of the system should be managed and reported.

Pipeline system integrity

The function of submarine pipeline systems is to efficiently and safely transport a variety of fluids. The pipeline system’s integrity is defined as the structural/containment function, which is the system’s ability to operate safely and withstand the loads imposed during the pipeline’s lifecycle. If a system loses this ability, a failure has occurred.

The RP defines two main failure modes relating to a pipeline’s containment/structural function:

• Loss of containment – leakage or full-bore rupture; and,
• Gross deformation of the pipe cross section, resulting in either reduced static strength or fatigue strength.

Pipeline system threats and damages/anomalities

An overview of typical threats to a submarine pipeline system (including onshore sections) and associated damage and anomalies is given in Table 1. A third-party threat, such as trawling interference, may cause a gouge in the pipeline surface which can, under certain conditions, act as an initiation site for fatigue-crack growth and subsequent rupture. Managing the risk related to such threats is essential for maintaining the integrity of a pipeline system.

Integrity management in a lifecycle perspective

Pipeline integrity is established during the concept selection, design, and construction (fabrication and installation) of the pipeline system, and maintained during the operations phase.

DNV OS-F101: Submarine pipeline systems gives criteria and guidance with regard to both integrity stages, with its main focus on the first stage. DNV RP-F116 also gives recommendations for both stages, but mainly addresses maintenance, with particular focus on the IMP. The IMP begins during the established integrity stage and it is carried out continuously throughout the entire life of operation, until abandonment of the pipeline.

The choices that are taken in the early design work, such as selection of pipe materials (carbon steel, stainless steels, clad-pipe, etc.), monitoring systems, inhibitor systems, piggability, buried or not-buried, the novelty or robustness of design, and quality of the design/construction/installation phases will be decisive for the inspection and monitoring programme developed and implemented in the operation phase.

If a pipeline has been inappropriately designed for its intended use and lifetime, then extra effort will be required during operations to ensure that its performance (regarding safety, environment, flow capacity, etc.) is acceptable. Similarly, an appropriately designed pipeline that is poorly constructed would be expected to experience similar challenges.

Further, if design and construction are acceptable but the in-service integrity management is inadequate, early loss of integrity becomes more likely.

Integrity is said to be transferred from the development phase to the operations phase: this interface involves the transfer of vital data and information about the system required for safe operation of the pipeline system.

Addition to DNV’s pipeline standard

The RP formally supports and complies with DNV’s recognised pipelines standard, according to which 70 per cent of the world’s pipelines are built. However, the recommendations can also be used separately and are also considered relevant for pipelines designed according to other codes such as ISO 13623, API RP 1110, and API RP 1111.

Extension of DNV RP-F116

The objective of the DNV RP-F116 development was to cover the entire pipeline system in consistency with the definition in the DNV OS-F101 offshore standard. However, the need to cover additional aspects in the RP and provide more detailed guidelines has already been identified through presentations at conferences and feedback from early use of the RP.

The topics listed below are examples of what has been requested by the industry:

• Working process for detailed risk assessment of individual threats;
• Third-party threats – inspection, planning, and damage assessments;
• Key performance indicators for monitoring of the IMS;
• Corrosion management of in-field and/or unpiggable pipelines;
• Shore approach and onshore sections;
• Flexible pipelines; and,
• Operations readiness.

On 9 March 2010, the industry was invited to attend an industry seminar to discuss relevant topics related to the operation of submarine pipeline systems. The industry was given the opportunity to influence and contribute to forming the scope of a forthcoming JIP for extending the DNV RP-F116, making the document more comprehensive than it appears at present. More such seminars will take place prior to establishing a scope and issuing a formal JIP during the second quarter of 2010.