This paper helps defining the Inspection, Monitoring, Maintenance and Repair requirements for the subsea and flowline systems.

  • Trees Systems & Subsea Structures
  • Pipeline systems (including production, water injection, gas lift and gas Injection
  • Rigid or flexible jumpers, spools & risers
  • Subsea control system, jumpers, dynamic risers, Instruments and monitoring elements
  • Topside located subsea system elements (Hydraulic Power Unit, Electronic Power Unit, Subsea Production Control System and supporting sub systems)

The objective should be to achieve optimized subsea and pipelines system integrity, expenditure (considering both CAPEX and OPEX) and availability through systematic application of risk assessment to drive:

A. Design of the subsea system accounting for:

  • Compliance with integrity control and management in line with DNV-RP-F116 (Integrity Management of Submarine Pipeline Systems)
  • Functionslity of the subsea and pipelines system to support operating requirements

B. Inspection, monitoring, maintenance and repair requirements to:

  • Demonstrate system vulnerabilities are Identified and addressed;
  • Validate assumptions made in design;
  • Validate compliance with Integrity requirements;
  • Facilitate operational compliance within system limits;
  • Allow Identification of degraded operation / performance and onset of failure;
  • Permit troubleshooting of faults.

All Inspection, Monitoring, Maintenance and Repair activities must address the following functional requirements:

  • Inspection: Allow determination of conformity to specified requirements by physical verification and assessment of components in order to detect changes (for example as-installed location and condition) as identified by comparison to a previous or baseline inspection
  • Monitoring: Allow determination of the status of a system, process, product, service, or activity by surveillance of relevant properties or the physical and chemical environment that a piece of equipment is exposed to, to determine if and when damage may occur, and (where relevant) predict the rate or extent of that damage
  • Maintenance: Those activities required (e.g. when applicable and/or required by design) at regular or planned intervals to prevent deterioration or failure of equipment, or to maintain reliability or performance before failure or unacceptable deterioration occurs
  • Repair: Those activities required to return failed and / or nonconforming equipment to a state in which it can perform its required function. Items must be packaged to allow removal and replacement.

Project specific risk-response assessments and an Inspection, Monitoring, Maintenance and Repair Plan must be generated during each lifecycle phase.

Optimization of Inspection, Monitoring, Maintenance and Repair functions and activities must account for potential grouping of activities depending on frequency and execution requirements. All Inspection, Monitoring, Maintenance and Repair activities must:

  • Be planned and resourced (vessel / tooling) to a level commensurate with the assumptions considered for application in the subsea & pipelines Inspection, Monitoring, Maintenance and Repair procedure
  • Align with the project requirements for sparing and tooling (Subsea Sparing and Tooling Philosophy)
  • Align with the project isolation philosophy (Subsea Isolation Philosophy)
  • Align with project requirements for logistics accounting for (but not limited to) berthage, warehousing and materials management
  • Align with the framework according to pipeline repair to address the risk and consequence of pipeline damage (addressing both flooded and non-flooded scenarios) and subsequent repair strategies


Monitoring must be the reference case for addressing requirements related to Inspection, Monitoring, Maintenance and Repair philosophy with inspection, maintenance and repair considered on a justify in basis.

Riser Monitoring

Full time integrity monitoring of the flexible riser system (throughout its length) during operations must be considered in design (as applicable) to demonstrate compliance with:

  • Overall system dynamic motions (both extreme and fatigue)
  • Performance of appurtenances
  • Design and operating assumptions and associated system performance
  • Integrity of overall pressure containment layer (e.g. riser annulus condition)


Inspection scope, when identified by risk analysis basis, must consist of planned underwater campaigns. Inspection techniques must be selected based on their suitability to manage risk associated with the particular failure scenario being considered in accordance with subsea & pipelines Inspection, Monitoring, Maintenance and Repair procedure.

Pipeline walking monitoring (if applicable and when required) should be in accordance with subsea & pipelines Inspection, Monitoring, Maintenance and Repair procedure and performed on a risk-based assessment of likelihood. The extent of flowline walking should be assessed and appropriate measurement/monitoring methodology incorporated to minimize ongoing OPEX spend.

Maintenance and Repair

There must be no planned maintenance of subsea facilities and pipelines with the exception of topsides based equipment which must comply with the requirements as per Offshore Facility Operations Philosophy.

Equipment designs must allow replacement of worn or failed components to be performed by diverless methodology.

Intervention for repair or replacement must be carried out on an as-needed basis should equipment fail in service.

Flowline Repair

The flowline repair system must consider the risk and consequence of flowline damage (involving both flooded and non-flooded scenarios). This strategy does not apply to flexible risers.

Initial response to an event, damage assessment and eventual repair of the flowlines must comply and be consistent with recommended pipeline repair system and associated pipeline repair plan, procedures, repair equipment, tooling, project specific connectors and spare linepipe (as applicable) must be established for the flowlines and handed over at or prior to ready for startup. A procedure should be developed to incorporate a combination of critical spares, tooling and procedures allowing an effective flowline repair to be executed during its design life. The procedure must cover all credible failure and repair scenarios. Development of the procedure must adopt an agreed state of readiness considering HSE and production outage risks associated with varying repair response times.

Design Requirements

The designs must comply with the following requirements:

  • The subsea system must be designed and manufactured with the objective of minimizing intervention and inspection frequency and complexity. The target must be zero planned maintenance for the subsea system
  • The subsea system must be provided with sufficient isolation (Subsea Isolation Philosophy)
  • The Inspection, Monitoring, Maintenance and Repair philosophy must address all likely requirements for intervention, maintenance and future expansion (see Subsea Futures Development and Expansion Philosophy) with no production impact
  • Critical components should be designed for replacement to be performed using a Remote Operated Vehicle (ROV) and/or Remote Operated Tooling (ROT) run from a suitable vessel. Critical components are defined as those with higher probability of failure and can affect the integrity and/or availability of the system (e.g. subsea control module)
  • ROV operations should be in accordance with the Engineering Standard and Guidelines to Autonomous Subsea IMR Operations
  • Valve interface, override design and location should be suitable for ROV intervention
  • Design must facilitate cleaning and capping of any exposed interfaces
  • Design must enable easy reconfiguration through swapping of hydraulic/chemical lines within subsea structures in case of component failure. i.e. configurable ROV stab plate / Logic Cap
  • Designed with industry standard connections to facilitate future monitoring and/or inspection systems
  • The design of subsea indicators, ROV interfaces and connection points should be designed to minimize visual and functional impact of the marine growth and calcification and retain functionality post cleaning operations
  • Each intervention scenario must accommodate an appropriate range of suitable and appropriated vessels
  • Facilitate vibration monitoring for piping/components that are susceptible to flow induced vibration