The Magazine for Underwater Professionals

Mar/Apr 2017

ASSOCIATION NEWS

Society for Underwater Technology

Subsea projects and lessons for the future

An audience of approximately 100 converged on the Robert Gordon Institute in Garthdee for the SUT Aberdeen Branch evening seminar on the theme of ongoing subsea projects and lessons relevant to the current straitened times in the subsea industry. A loss of CAPEX funding and OPEX cost-cutting has resulted in numerous projects being either cancelled or suffering severely curtailed budgets. But even under these circumstances our speakers were here to show how the right approach could still bring success.


Crawford Brown, Apache project manager for the Beryl Far North Terrace project, explained how even in the middle of this downturn, Apache was able to develop a four-kilometre single well tieback. The project went from sanction to first oil in 11 months by focusing on what could be achieved by use of existing designs and infrastructure. Under normal circumstances the well might not have been developed if a front-end engineering process had added cost and consumed time optimising production profiles and infrastructure options.

 

LIMIT
David Mitchell of Subsea 7 discussed the design, construction and installation of the Catcher subsea systems. With 90 metres water depth at the FPSO, the flexible riser system was on the limit of what could be achieved when accounting for mid-water arches, their foundations, vessel motion and the risk of riser clashing. Another feature of the project was the need to comply with third-party specifications at the export tie-in, adding time and cost in an environment in which the subsea industry is frequently discussing standardisation and ‘fit for purpose’ designs.


Tony Boyle of BP and Richard Wylie of Technip discussed the collaborative measures required to achieve efficiency on the Quad 204 redevelopment with the need to have multiple vessels working in close proximity. A key point was that by spending time engineering the process of performing repetitive subsea operations, a pipeline connector for example, each step of the procedure could be scrutinised to remove or improve it and by monitoring the efficiency improvements offshore, the team was able to justify the time spent on this amount of detailed engineering.


With such detailed stories to tell, it was not surprising that each talk overran by a few minutes. As a result, we kept the time for questions short, making for a livelier networking buffet afterwards, with all our speakers engaging with the audience members.


Martin Harley

The latest design and analysis challenges for advanced service valves

The SUT North of England Branch’s first evening meeting of 2017 was held at Newcastle University on an unseasonably warm evening. The event focused on the latest challenges involved in the design and validation of advanced service valves for increasingly onerous operating conditions.


The audience was welcomed by branch chair Michael Williams, managing director of PDL Solutions. He was followed by the chair of the evening, Elizabeth Waterman, senior engineer at PDL Solutions, who informed us of the evening’s agenda and introduced us to the first speaker – Malcolm Hay, project engineer at BEL Valves Ltd.


Malcom joined BEL Valves 10 years ago as an apprentice and having won apprentice of the year and the prestigious HT Lamb Award, has continued working within the valve industry and is involved with valve development processes from start to end. Malcom’s presentation focused on the design challenges valve manufacturers face to avoid valve failure and how these require stringent testing and design verification.

 

SPLIT
Malcolm’s presentation was titled Design Challenges and Verification of Valves to Keep Pace with Oil Field Development Rate. Malcolm jumped straight in with a project he had recently been involved with, and the difficulties faced with replacing a split gate valve which was leaking whilst in service – not supplied by BEL Valves! This valve presented many challenges: the fierce operating conditions (a large range of temperatures with a low pressure), it must fit within an existing valve system, be proven to seal under operating conditions (bore pressure and external loads) and meet the all standards for various tests. BEL Valves was faced with supplying a valve which provided a robust solution to these challenges whilst being under a tight development schedule.


The terminology of the split gate valve with visual aids along with the specific characteristics of this valve were explained. Using FEA (finite element analysis) models to test all of the design considerations is advantageous as it can relatively quickly and cheaply show which considerations would have a positive or no impact at all on the valves, and verify which design is best. The stringent testing and standards which must be met were explained in depth; FE testing to the client specification, FAT to API 6D and qualification and bending testing to the client specification. The bending test required the design of a new rig to test the external forces in all directions. The valve passed all of the testing stages (FEA and physical testing). Malcolm concluded by observing that the leaking of a valve can have a knock on effect with the necessary testing – key to providing the client with confidence in the design.

 

FOCUS
The next speaker was Lee Brimer, a senior engineer who joined PDL Solutions more than five years ago. He is heavily involved with valve designs and analysis and has worked with BEL on numerous projects. The focus of Lee’s presentation was to talk about the FEA process and how it is carried out to ensure customer confidence.


Lee’s presentation was titled Advanced Engineering Analysis as a Valve Design Verification Tool. Lee presented an overview of the typical analyses used in valve assessment using FEA, including structural (linear elastic and nonlinear elastic‐plastic), thermal and thermal‐structural (to mitigate gate jamming). The analyses included hydrogen induced stress cracking (HISC), relevant for Duplex materials, and various specific components, such as gaskets, bolting and trims.


The presentation focused on the FEA work carried out to validate the split gate valve designed by BEL Valves for the same project Malcolm discussed. Particular focus was applied to the performance of the valve design under large external loads, due to previous issues observed by the operator, to ensure that the valve sealing functionality was maintained. Lee described the FEA setup, involving a complex assembly model with non‐linear contacts, and outlined how the worst case loading was determined.

 

PRESSURE
The results showed the sealing pressure obtained and how that compared to the pressure required to maintain sealing. Lee showed how a valve capacity could be predicted regarding the maximum external loading that would be acceptable to maintain sealing. FEA was shown to be an invaluable tool in modelling valve operation early in the design process, in order to provide confidence in the design performance and to highlight areas for improvement.


The final speaker was James Brierley, a graduate project engineer at BEL Valves who is in a good position to assess the current challenges faced in valve production for onerous environments, having completed an R&D dissertation with BEL Valves.

 

EXTRACT
James’ presentation was titled Expected Challenges and Design Verification of HP/HT Valves Developed for Subsea Service. The motivation for the talk was that, as oil resources have become more depleted, further oil field discoveries require engineering for more onerous conditions to extract the oil. The particular focus for the presentation was high pressure and temperature conditions, at which BEL Valves has led the way in terms of valve development for some of the biggest projects in the subsea engineering sector.


James described the particular regimes involved in high pressure, high temperature and soar service environments for valve operation and various associated problems, such as corrosion, how to maintain valve function over its lifetime and how to comply with safety integrity levels (SIL). The importance of high integrity pressure protection system (HIPPS) valves in protecting subsea piping networks was described, along with the development of valve sizes and operating conditions over time. It was detailed how specialist materials were required under the conditions for corrosion resistance and to reduce friction, such as tungsten carbide and the development of diamond‐like carbon (DLC) coatings.


The development of analysis techniques over time was described. FEA has moved from simple linear elastic assessments to assembly models with nonlinear contacts, to nonlinear material models and fatigue assessments. James offered a view about how the future of FEA will involve assessment of fracture mechanics. In terms of computational fluid dynamics (CFD), analyses have moved from single phase to multiphase, and assessment of HIPPS valve closure times. An advantage of analysis was explained in terms of being able to reduce the size and weight of valve components and therefore minimise cost. James concluded the presentation with a description of the rigorous testing regime required to mitigate the risk of valve failure.


Thanks go to the speakers for their time and effort in delivering the presentations, and to PDL Solutions and BEL Valves for their sponsorship.

 

Eugenie Warden and Nick Brown

 

 

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