DNV undertakes classification, certification, and other verification and consultancy services relating to quality of ships, offshore units and installations, and onshore industries worldwide, and carries out research in relation to these functions. Provide principles and procedures of DNV classification, certification, verification and con- sultancy services. Provide technical provisions and acceptance criteria for general use by the offshore industry as well as the technical basis for DNV offshore services. Provide proven technology and sound engineering practice as well as guidance for the higher level Offshore Service Specifications and Offshore Standards.
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Pipeline subsea repair. Edition November The documents are available free of charge in PDF format. DNV GL recommended practices contain sound engineering practice and guidance. Any comments may be sent by e-mail to rules dnvgl. DNV GL does not accept any liability or responsibility for loss or d amages resulting from any use of this document.
Changes — current. Text affected by the main changes in this edition is highlighted in red colour. However, if the changes involve a whole chapter, section or sub-section, normally only the title will be in red colour. Main changes November Page 3. B Fitting capacity. C Typical tests. A - Code breaks and design factors.
D - Stress analyses for fillet welds. E - Design resistance; welding on a pipe in operation. F - Calculation example - mechanical coupling axial locking capacity. G - Pipeline risk assessment and failure statistics. H - Guidelines - longevity of polymer seals. I - Recommended practice on the fatigue strength of pipes with ring marks in the base material.
Editorial corrections. In addition to the above stated main change s, editorial corrections may have been made. Page 4. Basic philosophy. Pipeline repair activiti es. Page 5. Preparedness strategy. Pipeline design basis. Pipeline exposures. Fitting design. Page 6. Local radial expansion loads. Seal capacity. Installation and attachment to the pipeline.
Isolation plugs. In-line isolation period. Hot tapping. Above water tie-in. Failure modes. Structural integrity. Page 7. Welding procedure qualification. Production welding re quirements.
General requirements. Documentation and quality assurance. Page 8. Code breaks and design factors. Fitting capacity. Typical tests. Stress analysis of fillet weld. Design resistance; welding on a pipe in operation. Calculation example - mechanical coupling axial locking capacity. Pipeline risk assessment and failure statistics. Guidelines - longevity of polymer seals.
Recommended practice on the fati gue strength of pipes with ring marks in the base material. Checklist for qualification.
Page 9. Revision history of this recommended practice RP :. The overall integrity management system and the integrity management process, including a more detailed description of these activities , are covered by DNVGL-RP-F Integrity management of submarine pipeline systems. Figure Integrity management system, ref. Page This RP applies to fittings used to repair and tie-in submarine pipelines. These fittings include: couplings, clamps, T-branch connections and isolation plugs. The RP provides guidance on pipeline repair method s such as pipeline hot tapping and above water tie-in.
In addition, recommendations and guidelines on pipeline preparedness strategies, pipeline damage assessments and testing are given in this document. Figure gives an overview of typical fittings covered in this document. Figure Typical installed repair fittings. Repair coupling with flange adapter.
Welded split sleeve repair clamp. Couplings connect pipes by being directly attached to th e pipe walls via mechanical or welded joints. Flange connectors differ from mechanical couplings as flanges join pipes via thick, machined pieces of additional material that are welded or forged onto the pipe ends prior to installation. Hot tap T-branch connections are fitted externally to the pipeline assembly during operation. Pipeline isolation plugs are pumped with the suitable flui d to the repair site and then activated in order to form an isolating barrier that can resist differential pressure, or the isolation plug can be installed locally via hot tap penetration.
The pipe itself represents the key member of the repa ir assembly, with consequential limitations such as, but not limited to, pipe wall strength, surface irregulari ties and deviations in shape.
Pipeline repair fittings must be installed with caution to reduce the likelihood of damage, e. The fitting's coupling strength shall be sufficient to resi st stresses from all relevant loads, within a factor of safety as defined in [6.
The section [6. The given load and resistance factors to be accounted for in the fitting strength capacity are based on pipelines designed and manufactured according to DNVGL-ST-F For the repair of pipelines designed according to other standards, the desi gn factors applied must be assessed.
Some fittings will be a permanent part of the repair ed pipeline, while others like isolation plugs are installed temporarily to enable the repair process, see [3. Further, an overview of typical pipeline repair proj ect activities, including the root cause and integrity assessment of the damage, selection of the repair method and pipeline repair strategy Sec.
Pipeline damage that may require repair is typically caused by degradation mechanisms such as internal and external metal loss due to corrosion or hydrogen in duced stress cracking HISC , or by events such as unstable seabed conditions, anchor hooking, trawl gear interference and objects dropped from the surface. The risk of damage depends on the intensity of surf ace activities such as ship transport and offshore operations as well as the depth, seabed conditions and design and operation of the pipeline itself.
The extent of possible damage will vary from insignificant to a fully buckled or severed pipeline. Consequently, the repair and repair preparedness strategy must be based on all these factors. Pipelines are accepted as a safe form of energy transportation and the industry has many years of operational experience. However, pipeline failures do oc cur. Learning from pipeline failures is important and can help to reduce future failure risks through the impl ementation of mitigating measures such as a repair and repair preparedness strategy.
Th e failure probability and type vary in different parts of the world, depending on design philosophies and risk exposures, and need to be accounted for when utilizing the data. Reports on public pipeline failure statistics are limited, but some of the available data are presented below:. The database also covers all types of offshore cables used in the petroleum activities and is continuously updated.
In addition, fitting, flange and valve failures are a major problem. The pipeline damage statistics vary for different parts of the world, but th is RP on pipeline repair is applicable worldwide. Incidents connected to fittings and valves in the North Sea, whic h were app. Figure illustrates the complexity of a subsea pipeline repair. Figure Typical support system for a pipeline repair.
Historically, shallow water repairs have mostly been performed by divers. Howe ver, the water pressure limits human hyperbaric intervention to a water depth of a few hundred metres due to the human physiology.
National authorities further regulate this type of diving to more shallow depth limits as a means to safeguard the divers.
DNVGL-RP-F113 Pipeline subsea repair
DNV RP F113 - Pipeline Subsea Repair
DNVGL RP F113