Integrity management and Engineering

Z-Subsea asset (Pipeline, Subsea, Riser and Topside facilities) integrity Engineering group provides integrated full life cycle services to the oil and gas industry. The group involvement starts from Concept/Design phase and continues to Construction, Procurement, Fabrication, Installation and Operation phases. Due to the growth in the number of aged assets in regions such as North Sea, the group specifically offers specialised services beyond the design life or assets Life extension.


In summary, the group provides consultancy services to the oil and gas industry on the following specialised areas:

Risk Based Integrity Management

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Risk-based approach is now a well accepted method in the industry for managing integrity of the oil and gas systems. DNV RP-F116, Energy Institute guideline and ISO/ASME are amongst available procedures developed based on the risk-based approach.

At Z-Subsea we assist our clients by providing risk-based integrity management following and providing expertise in all the steps below:


  • Itemizing large assets into smaller sub assets and components
  • Identifying threats and their associated failure mechanisms for each component employing analyses such as Failure Modes and Effect Analyses; FMEA or Failure Modes Effects and Criticality Analyses; FMECA
  • Calculation of probability and consequences of failure (Qualitative or Quantitative)
  • Calculation of Risk
  • Construction of a project-specific Risk matrix incorporating client's corporate risk matrix
  • Highlighting high risk areas require remediation (design alteration, operational change and/or more frequent inspections).
  • Running Risk Assessment workshop inviting client's technical representatives in order to  finalizing an acceptable Risk matrix specific to the project.
  • Determination of inspection intervals for the assets of interest as an ongoing process.
  • Issuing project-specific integrity management reports summarizing the outcome of the Risk assessments
  • Development and implementation of Inspection, monitoring, maintenance and repair philosophies. 
  • Development and implementation of the Pigging Feasibility study reports
  • Audit and review of the produced integrity management reports should any change in operation and service is identified (Management of change)


At Z-Subsea we see the added value of engaging with our clients on the integrity management subject from the conceptual project phase as we believe that our clients will benefit economically as well as technically post incorporating outcome of the risk-based integrity management (IM) performed during the conceptual phase into the design stage as any design change at early stages is deemed to be less expensive, technically feasible. 

Life Extension and Remaining Life Calculation

As part of this study, Z-Subsea could perform remaining life calculations for the existing assets which may require operation at a higher operational condition, longer life and change in safety margin as a result of a new Tie-in, capacity increase, and or new field development

With many offshore installations in the UK and Norwegian sector of the North Sea now reaching or being in excess of their original anticipated design life, usually 20 years, there is a particular need to evaluate approaches to the structural integrity management by offshore operators. Ageing processes can affect the structural integrity of the installation and demonstration of adequate performance beyond its original design life is thus a necessary requirement.

At Z-Subsea we provide Life Extension (LE) assessments consultancy to operators and/or Independent Verification Bodies (IVB) on the aged oil and gas assets based on the procedures outlined in NORSOK N-001, ISO 19900/19902, ISO13822 and API RP2A-WSD.

At Z-Subsea, we follow the following steps during any LE process for our clients:


  • Gathering relevant historical and current data from the asset
  • Generating values not available such as applied stresses using Finite Element Analysis (FEA) techniques, pushover/Redundancy analysis, etc.
  • Understanding of the degradation processes on the asset with reference to earlier Risk Assessments reports, inspection data, etc., if available. If none available, Z-Subsea could perform risk-based integrity studies to overcome this gap (Section 6.1).
  • Use of best technology / latest assessment methods to determine remaining life and safety margins on the asset and hence checking the need for repair
  • Development of new techniques (e.g. online monitoring) implementation strategy

Engineering Criticality Assessment (ECA)

ECA or Engineering Criticality Assessment is a Fracture mechanics based approach in that significance of cracks and crack-like features either in the weld (Lack of Fusion, Lack of Penetration, Slag inclusion, etc.) or in the parent metal (Lamination, Lamellar tearing) on the integrity of an oil and gas component is assessed. This approach is proved to be very cost-effective as it avoids unnecessary repairs.

Z-Subsea integrity team has been actively involved in the development of the ECA related codes/standards such as BS7910, DNV OS-F101 (Appendix A), SINTAP and FITNET and use of codes such as DNV RP-F108, API579-1/ASME FFS-1. That said we are confident that we are aware of the cutting edge developments on the relevant/international standards which could be easily pass on to our client in their projects.

At Z-Subsea, we have in-depth knowledge of using the ECA approach during the projects full life cycle (from the conceptual phase, Fabrication, Construction, Operations up to the end of asset life) and beyond (Life extension) under both static (Fracture) and cyclic loading (Fatigue). Engineering Criticality Assessment (ECA) of installations and operations in extreme conditions, i.e., strain-based installations (Reeling or installations in the deepwater), High Temperature and High Pressure (HP&HT) operations and exposure to the hostile environments such as sour-service (high level of H2S), are also  amongst Z-Subsea cutting edge expertise and in-depth knowledge on the subject.

The outcome of the ECAs would be in forms of tolerable defect sizes (acceptable flaw depth versus defect length) for a project full life cycle, indication of fatigue life of a welded/non-welded component and determination of the inspection intervals.   

Managing Specialised Mechanical Testing

At Z-Subsea we plan, manage, and witness mechanical tests on the welded/non-welded oil and gas assets such as pipe materials, welds, risers, and pressure vessels in order to obtain required materials input data for the integrity assessments (ECA/FFS) or as part of the welding qualification procedure.

At Z-Subsea, we could perform and manage standardized and tailor-made mechanical tests such as:


  • Round/Flat tensile tests to EN100012
  • Standard and sub-size V-notched Charpy tests
  • Fracture toughness tests (CTOD/J) on Single Edge Bend Notched (SENB) and Single Edge Notched Tension (SENTS) specimens and determination of single value of fracture toughness and J/CTOD-R curves to BS7448, DNV RP-F108 and other relevant standards approved by the client
  • Testing of segment specimens extracted from pipelines of interest
  • Full-scale/pressure testing of the pipes


In case such experimental data are available, Z-Subsea experts will review, assess and upgrade testing reports in case any change in the material and operations have been introduced to the oil and gas system.

Failure Investigation

Z-Subsea integrity and materials engineering groups as a common practice team up in order to manage failure investigations by focusing on facts finding studies, data gathering and interpretation and reporting.  

Fitness for Service (FFS) Assessment

FFS or Fitness for Service assessment is an approach is being used in the oil and gas industry in order to assess safe continued operation of assets at presence of defects such as Corrosion (local and general metal loss), dents, gouges, etc. The assessment requires analysing the past and recent inspection data, usually in forms of NDT or In-Line Inspections (ILI) data, listed all the anomalies detected as a result of the inspections.


As part of ay FFS assessment, Z-Subsea integrity experts perform the following activities:


  • Review and analysis of the recently gathered NDT and ILI reports and matching/comparing that with the historical data gathered for the similar asset in order to establish the growth rate variation over the time (Box or signal to signal matching)
  •  Highlighting the most critical features that need immediate integrity assessment
  • Calculation of safe working pressure for the asset at presence of those critical features according to DNV RP-F101, API579-1/ASME FFS-1, RSTRENG, PDAM, etc.
  • Calculation of Remaining life of the asset at presence of the critical features, grown at a rate which is usually calculated by Z-Subsea flow assurance/process engineers or during the box or signal matching exercise
  • Calculation of the inspection intervals
  • Development and implementation of the repair procedures and philosophies