In the interests of efficiency and reliability it’s necessary for umbilical systems to be tested and cleaned at regular intervals and after production. For this purpose, RMI Pressure Systems has developed a new test rig with all the necessary approvals for onshore/offshore use which allows for streamlined cleansing and pressure testing in-situ.
As the name suggests, the umbilical system is the lifeline for the subsea structures used in offshore oil and gas production. It provides the link from the host facility through which control is exercised, power is transmitted and utilities such as injection chemicals are supplied to the subsea wells. With the continuing trends in subsea to shore installations and operations in deeper and deeper locations, umbilical systems are subjected to increasing levels of stress.
The umbilical is a long, flexible construction - its length can be anything from a few miles to more than 180 miles - which consists of tubes, cables, armouring, fillers and wrapping contained within a protective sheath.
The multiple functions it performs and the demanding environment in which it is installed and operates, mean that the umbilical is necessarily a very hi-tech product which must perform reliably while in operation.
The critical nature of the systems and valves which are controlled by the hydraulic umbilicals throughout the subsea networks, requires that the hydraulic fluid be cleaned strictly in accordance with the industry’s specifications. The lines and connections must also be regularly checked for leakage to ensure that they operate correctly and with the necessary reliability and efficiency. In order to carry out the cleansing and checking procedures a test rig is required which is capable of flushing out the entire umbilical length and submitting it to a pressure test.
Hitherto, the size of the pump needed for the operation meant these tests were traditionally carried out onshore, which added to the complexity of the logistics and rendered the process rather inefficient. To improve the efficiency of the client’s process, a leading manufacturer of bespoke umbilical products, wanted to develop a test rig which would be suitable for offshore use. The list of design criteria was long and exhaustive.
The new test rig had to be enclosed in a custom steel framework which would allow it to be lifted by a crane and also be able to fit inside a standard cargo container. With the dimensions of the rig established, the heart of the system would be the high pressure pump, which would have to be capable of producing pressures up to 15,000 psi (1,035
bar) with flows between 3 to 15 US gallons/min (11 to 56 litres/min).
Achieving these figures would reduce the overall time required to fill, flush
and pressure test the umbilical system, which in turn would reduce the cost of the installation. With the test rig being designed for offshore use, it was essential that the pump offered the highest level of reliability.
In addition to these standard requirements, and to make it suitable for use on the pumping platform, needed to be intrinsically meeting Class I, Div II classification offshore and onshore rig was also required fluids being used in procedure to ensure the umbilical were not contaminated.
The filtration package requires 3 micron filters installed on both the suction the pressure sides of reservoir to prevent contamination during the testing procedures.
Additionally, two filters were added to minimal contaminants the reservoir.
RMI Pressure Systems meeting this challenge, design of the steel frame of the test rig on its Trimax S250 high pressure pump. The pump is controlled by a Toshiba variable frequency drive (VFD) and Omron PLC and is suitable for both the flushing operation and the high pressure testing. Using a single pump for both procedures reduces the overall
operation time which in turn reduces costs. RMI’s Mike Sherman takes up the story:
“In the past the client had contracted out the task of testing and flushing its umbilical systems, but there was a requirement to bring these operations back ‘in-house’, which would allow greater The completed test rig provided this facility with a much more efficient pump, providing substantial savings in time, six days down to two days, and money to complete the testing and flushing operations.”
The Trimax range of crankshaft-driven, reciprocating pumps provides high efficiency
pumping at pressures up to 1,050 bar and flows up to 610 litres/min. The S200 and S250 are both three piston, crankshaft driven, positive displacement pumps.
The design of the pumping system enables the units to operate in hazardous conditions without modification; however, to meet the intrinsically safe specification for the entire
test rig, several modifications were required, including the installation of a nitrogen
purge system for the VFD and various explosion-proof fittings.
All of the pumps are fitted with a robust, fully supported crankshaft with con-rods assembled with lead bronze big- and small-end bearings. Extremely high wear-resistant solid ceramic plungers, combined with Kevlar fibre seals provide long-lasting, high-pressure sealing. All pumps undergo a rigorous testing programme prior to dispatch, which includes oil temperature and pressure checks plus vibration monitoring, as well as the normal pump performance criteria.