Subsea Accumulator Module (SAM)
Subsea Accumulator Module (SAM)
The SAM, illustrated in Figure 3-13, is the subsea unit that stores hydraulic fluid such that adequate pressure is always available to the subsea system even when other valves are being operated. SAM is used to improve the hydraulic performance of the subsea control system in trees and manifolds. Basically, it will improve hydraulic valve actuation response time and system hydraulic recovery time, at minimum system supply pressures.
Description
When a subsea system is required to operate a number of trees located a long distance away from the host, the hydraulic fluid from the topsides HPU will take a considerable time to reach the subsea equipment, particularly where small hoses are used in the umbilical. This can result in a drop in pressure at the subsea tree when a valve is opened, as the pressure cannot then be restored immediately via the umbilical. If the pressure drops, other open tree valves may begin to close, before the pressure can be restored.
If the pressure drops too much, the pilot valves in the SCM will “drop out,” that is, close, causing one or more tree valves to close irrespective of whether pressure is then restored via the umbilical. To maintain an adequate level of pressure at the subsea location, some degree of local accumulation may be required. This can be provided by individual accumulators on the SCM itself, but more usually, a self-con- tained skid containing several accumulator bottles is often provided, this being termed a subsea accumulator module or SAM. The SAM will house sufficient LP accumulation to maintain pressure during valve operations. In addition, it is also sized to hold sufficient fluid to perform a number of subsea control operations, even if the supply from the surface no longer functions, thus giving a degree of reserve power. A trade- off must be made against the size of skid required and the amount of accumulation and this is done via a hydraulic analysis performed by the manufacturer against the specifications. Sometimes the analysis will demonstrate that HP accumulation is also required. The requirement for an increased nitrogen precharge pressure in deepwater applications will decrease the efficiency of subsea accumulation, which will increase the number of accumulator bottles required.
References
1. P. Collins, Subsea Production Control Umbilicals, SUT Subsea Awareness Course,
Houston, 2008.
2. T. Horn, G. Eriksen, W. Bakke, Troll Pilot - Definition, Implementation and Expe-
rience, OTC 14004, Houston, 2002.
3. International Standards Organization, Petroleum and Natural Gas Industries – Design
and Operation of Subsea Production Systems – Part 8: Remotely Operated Vehicle
(ROV) Interfaces on Subsea Production Systems, ISO 13628-8/API 17F, 2002.
4. International Standards Organization, Petroleum and Natural Gas Industries – Design
and Operation of Subsea Production Systems – Part 4: Subsea Wellhead and Tree
Equipment, ISO 13628-4, 1999
5. National Aerospace Standard, Cleanliness Requirements of Parts Used in Hydraulic
Systems, NAS 1638-64, Class 6, 2001.
6. International Standards Organization, Hydraulic Fluid Power – Fluids – Method for
Coding the Level of Contamination by Solid Particles, ISO 4406, 1999.
7. Deep Down Company, Subsea Accumulator Module, <http://www.deepdowncorp.
com/deepdown/products/sams>.
