- Published on Wednesday, 21 April 2010 01:00
- Written by Luigi Cannistraci
As exploration for new oil and gas sources goes deeper into the ocean and further from shore, valves in service to that industry will have new pressure, temperature and durability requirements.
Despite short-term reduction in exploration activity caused by the recent global recession, world energy demand continues to grow, which will fuel an explosion in offshore exploration over the next decade.
Deep and ultra-deep prospects will continue to eclipse mature shallow water hydrocarbon production, which has seen a decline in capital expenditures in recent years. Thanks to major technological improvements and deep water exploration and production successes, the definition of deep water has changed over the last decade—passing from a threshold of 200 meters to over 1,000 meters. What was considered deep 20 years ago is now considered shallow; and the greatest potential is now represented by fields located at depths of over 1,000 meters. In fact, most new projects under development today range between 1,000 and 2,000 meters. These deeper (than decades past) water projects—together with increased distances from shores and increasingly harsh environments—represent the next frontier in exploration, production and transmission. This deepwater shift also is driving technology changes across many subsea components, including risers, connectors, separators, pumps, inspections, umbilicals and valves.
As far as valves, many new challenges in the high-pressure, high-temperature subsea environment exist, including the need to develop special alloys, coatings, elastomers and thermoplastics that can withstand the rigors of ultra-deep operation. For subsea actuation, new forms of power sources are under development. In addition, challenges that impose further demands on technology have been added to the mix through harsh arctic environments (where large reserves potentially reside); through ice and ice load, through short intervention windows, and through zero pollution requirements and zero discharge regulations.
A UNIQUE CHALLENGE
One situation that differentiates subsea valves from even nuclear valves is the desire to meet zero maintenance for the life of the valve. This means an operating life of more than 25 years, and in some cases up to 50 years. When you consider that true subsea valves must operate in water depths of thousands of meters, far from shore, where maintenance is simply not possible, you understand why the design and manufacture of these valves is unique.
Add to that reality the fact that subsea valves will be in service in very sensitive environmental areas such as Barents and other Arctic seas, where a valve failure could cause a dramatic environmental impact, and you see why we must also add another mandatory requirement—zero risk of emission to the environment.
With the above criteria in mind, the essential design and manufacturing characteristics of a subsea valve require:
- Materials that are corrosion resistant (CRA), verified and tested during the whole process with mechanical features that meet or exceed limits of acceptability—documented and traceable at the highest level.
- Design verified with the most modern software and the most demanding criteria.
- Mechanical components created with the most advanced machine tools to achieve dimensional accuracy, tolerances and repeatability considered unattainable only a few decades ago.
- Cladding carried out by robotic processes to reach and guarantee the highest possible quality, ensuring life-long valve cycling without failure.
- Soft component materials, elastomers and thermoplastics selected and formed to the degree they do not introduce any element of failure risk. Rubber is the most common soft component for other types of valves, but because of the possibility of degradation through aging, rubber can’t give the guarantee required for a valve that needs to be maintenance free. Soft sealing is used, but only as backup for the most precise and durable metal-to-metal primary sealing.
- Metal-to-metal seat-to-ball interface dynamic sealing by hard coating such as HVOF (high-velocity oxygen fuel). This is a significant factor in the reliability analysis.
- Once assembled and tested, a subsea valve has to pass a second level of demanding gas tests ensuring both safe and reliable operation of the valve before it’s placed in service.