DNV’s initiative to improve pipeline design and installation to ensure safe operations
The DNV Standard ST-F101 Submarine pipeline systems (with the latest August 2021 edition and earlier versions) is the world’s most widely used standard for offshore pipeline design. Approximately 75% of new submarine pipelines in the energy industry worldwide are designed and installed to this code.
Design, installation, operation
Traditionally, pipelines are used for the transport of natural gas over long distances, and in the energy transition natural gas will still be very important. Unfortunately, 73% of new gas fields and gas resources contain high levels of CO2 and H2S - posing a major challenge for the design, installation, and operation of the pipelines. Once the CO2 has been sequestered and the acid gas removed, the CO2 will be injected in subsea depleted gas wells. Some of the natural gas will be steam reformed to hydrogen and for this purpose, pipelines for CO2 and hydrogen transport are required. Green hydrogen from electrolyses using sustainable electricity and blue hydrogen generated from natural gas by steam methane reforming or enabled by carbon capture and storage needs to be transported in pipelines. Hence, pipelines are a very important element to facilitate the energy transition.
Due to the importance of the DNV pipeline standard ST-F101, DNV Pipeline Committee Meetings have been arranged twice a year for the past 25 years. The main objective of these meetings, attended by the energy industry majors, engineering contractors and manufacturers of pipelines is to obtain feedback to improve the pipeline standard and the associated recommended practices. Additionally, an important component in the meetings is to discuss the latest technology developments in pipeline design, installation, and operations.
In connection with the 49th DNV Pipeline Committee Meeting held at DNV Groningen on 19 April 2023, a workshop was led by DNV’s Dr Jens Tronskar to obtain feedback from pipeline operators and engineering, procurement, construction, and installation contractors to update the Recommended Practice DNV-RP-F108 Assessment of flaws in pipeline and riser girth welds, which was last amended in September 2021.
Workshops
The intent in arranging this workshop was to consider the significant comments that had been received by several parties and users of the DNV RP, indicating the need to update the document. The update applies primarily to Appendix C, which provides guidance on materials and girth weld testing for sour service. This RP provides guidance on assessments to develop flaw acceptance criteria for automatic ultrasonic testing (AUT) of the girth welds during offshore pipeline installation accounting for its future operation until its end of life. The workshop was attended by 40 participants from energy companies, pipeline operators, EPCIs and pipe manufacturers.
The invited presenters, Dr Bostjan Bezensek (Shell), Laurent Pomie (TechnipFMC), Dr Hu Bin (Allseas), Varun Prakash (McDermott) and Dr Mark Fryer (Subsea7) and the following discussion highlighted a number of issues which require follow-up. As a result, Dr Tronskar arranged a series of workshops following the DNV Groningen event, with the support of DNV colleagues Dr Wu Youyou (Singapore), Dr Ramgopal Thodla and Dr Gui Feng (Columbus), Dr David Baxter (Aberdeen) and Dr Erling Østby (Høvik). These workshops each attended by 37 to 50 participants from major energy companies and EPCIs globally, covered the following topics:
- Workshop 1: Pipeline design limits for sour service and material testing requirements - facilitated by Dr Bostjan Bezensek, Shell on 30/05/2023
- Workshop 2: ECA materials input data - facilitated by Dr Jens P. Tronskar, DNV on 23/05/2023
- Workshop 3: Welding/AUT - facilitated by Dr Jens P. Tronskar, DNV on 24/05/2023
- Workshop 4: Laboratory testing procedures - facilitated by Dr Wu You You, DNV 25/05/2023
- Workshop 5: Hydrogen pipelines and pipeline re-purposing for hydrogen is confirmed to be held on 29/06/2023 facilitated by Dr Erling Østby, DNV
Mentimeter survey
As part of the design limitations for sour service and materials testing workshop, a Mentimeter survey was performed. This showed that most companies use the DNV pipeline standard and the DNV-RP-F108 as a basis for the design philosophy, design and material selection and installation requirements for sour service pipelines. Eighty percent (80%) of the people surveyed answered that they use DNV-RP-F108 and Engineering Critical Assessment (ECA) as a basis for the early design of sour service pipelines and especially for severe sour service.
The survey results showed how important the DNV pipeline standard and the DNV-RP-F108 is to the energy industry. It is expected that these codes will be important for CO2 and H2 pipelines, for new designs and construction or for re-purposing of existing natural gas pipelines.
Update of guidance
A major outcome so far of the workshops is a proposed R&D project for the update of guidance related to fracture toughness and fatigue crack growth rate in sour environments. In sour service, the weld fracture toughness is significantly reduced (3-15 times depending on the severity of the environment) and the fatigue crack growth rates can be 30 to 130 times higher than for a natural gas pipeline.
For fatigue, the current guidance in DNV-RP-F108 takes the form of an equation to derive a fatigue crack growth rate acceleration factor, from environmental parameters pH and H2S partial pressure.
A work pack is proposed to provide updated guidance based on a review of available fatigue crack growth rate data obtained by testing carried out by energy companies, EPCIs and DNV. A much wider dataset is now available, compared to the SAFEBUCK JIP, which was the basis for the current equations in the DNV-RP-F108. The review will require JIP participants to donate data to the project. The data can be anonymized to remove any confidential information.
After collating donated data, DNV will develop more sophisticated models for predicting fatigue crack growth rates, as a function of key environmental and loading parameters. Its aim is to model the influence of cyclic loading frequencies and applied stress intensity range factors which are expected to be critical. Similar to sour service, high pressure hydrogen gas degrades the material and weld fracture toughness and increases the fatigue crack growth rates.
For the future design of hydrogen pipelines and the reuse of natural gas pipelines for hydrogen transport, these R&D initiatives are expected to serve as a model to develop guidance for the integrity assessment of hydrogen pipelines.