DNV released a new revision of Submarine Pipeline Standard—DNV OS F101, effective Nov. 13, 2007, harmonizing the existing standard with ISO, increasing its focus on integrity management, and improving the document’s structure.
The revised Submarine Pipeline Standard complies with the new ISO 3183 on line pipe material, with additional and modified requirements that make it the only pipeline standard in compliance with ISO 13623 on pipeline design. The DNV standard also increased its focus on the integrity of operational pipelines.
ISO harmonization
Newly revised ISO 3183, the material standard for C-Mn steel line pipe, triggered revisions to DNV-OS-F101. DNV wants to harmonize its standards with the ISO codes, with DNV-OS-F101 focusing on both ISO 3183 (material) and ISO 13623 (design). The new revision of ISO 3183, a merger between the old revision and API 5L, sought to bring US and global standards into conformity.
DNV chose to provide a self-contained standard instead of providing additional requirements to ISO. ISO requirements are repeated, with any additional or modified requirements clearly marked, including revision of the welding and nondestructive testing requirements. The component section also now reflects new ISO standards. DNV intends this document to stipulate most of the additional requirements purchasers normally specify regarding ISO-API.
The update also improves requirements regarding in-service pipelines, introducing new integrity-management system requirements and adding a separate section on documentation.
The document now subdivides the pipeline life cycle into concept and business development, design, construction, operation, and abandonment. All the standard’s sections now refer directly to one of these phases, and some of the contents have been moved to fit the new structure.
DNV introduced a new section, “Design—materials engineering,” that includes design-phase requirements relating to material selection, corrosion, sour service, hydrogen induced stress cracking, and other topics.
Modifications made regarding pipeline design were minor. Most changes constitute fuller interpretations of already existing guidelines and do not alter requirements. Pressure definitions, however, did change and the slightly modified criteria clarify requirements regarding the pressure protection system.
DNV course
DNV offers a course covering modifications to pressure and design criteria and introducing the structure of the line pipe section, including ISO 3183 requirements.
The course also includes modifications to components and referenced ISO standards and installation and operational requirements, and addresses the latest updates to welding and NDT requirements. The course targets engineers who have already been using DNV-OS-F101, 2000.
Software
DNV also offers software for checking code compliance. The code-compliance software is programmed in Excel-Visual Basic and includes the following checks:
- Burst (pressure containment) related to system test condition and operation.
- Collapse.
- Propagation buckling.
- Load-controlled load interaction (moment, axial force, and overpressure).
- Displacement-controlled load interaction (axial strain and overpressure).
The program calculates minimum required wall thickness for given conditions and use based on a wall thickness given by the user. The program also includes report sheets meant for paper printout and inclusion in reports, containing all relevant input, some intermediate data, and results from the check.
RP updates
DNV issued updates to recommended practices RP F109, On-Bottom Stability Design of Submarine Pipelines and RP F110, Global Buckling of Submarine Pipelines in October 2007.
Updates to these publications followed DNV’s call earlier in the year for two joint industry projects addressing integrity management of subsea pipelines. The first JIP, managed by DNV Høvik, invites oil and gas companies, survey companies, and other interested parties to participate in developing DNV Recommended Practice RP-F116, Subsea Pipeline System Integrity Management.
DNV Houston is managing the second JIP, developing a “Guideline for the development of a Subsea Pipeline Integrity Management Program for the Gulf of Mexico.” Pipeline owners and operators in the Gulf of Mexico are funding this JIP. Current industry practices, a significant percentage of unpiggable pipelines, local regulatory requirements, and Gulf of Mexico reporting requirements require establishment of a local guideline for pipelines in this area.
The results of this JIP will be referenced or incorporated into DNV RP-F116. Preliminary input from both JIPs informed the integrity-management content of the updated DNV OS-F101.
Operators currently apply onshore standards, such as API1160 “Managing System Integrity for Hazardous Liquid Pipelines” and ASME B31.8S “Managing System Integrity of Gas Pipelines,” and their own integrity-management systems to offshore pipelines, according to DNV.
DNV introduced the JIPs in response to the pipeline industry’s recognition of:
- An aging pipeline system.
- The lifetime extension and requalification of existing pipelines.
- Optimized design, which implies a stricter need for monitoring.
- Novel designs producing new challenges.
- The introduction of pipeline integrity-management standards for onshore pipelines (API1160, ASME31.8S).
The output from both JIPs will address in-service issues of concern, from early design through operation. The development and use of DNV RP-F116 and the guideline for the Gulf of Mexico will increase focus on the operational phase from the early design phase, allowing a better inspection and maintenance regime and reducing operational costs, says DNV. Operators can also use the RP to document compliance.
The Gulf of Mexico guideline will identify the components of a subsea pipeline integrity-management program and provide a detailed framework that producers or pipeline operators can use when preparing integrity-management programs for their own pipeline systems.
The guideline will also include a detailed framework for a direct-assessment methodology, which would be applicable to unpiggable subsea pipelines and will be submitted to the National Association of Corrosion Engineers, International (NACE) for review and approval.
Both DNV RP-F116 and the Gulf of Mexico guideline are intended to apply to subsea pipelines, both piggable and unpiggable, which transport natural gas or hydrocarbon liquids, and will address integrity management relating to both internal and external corrosion as well as other relevant threats to the system, such as free spans and third-party damage.