Proserv adds pumps for subsea work

Hydrostatic pressure testing and flushing subsea umbilicals for the offshore oil and gas industry is a relatively complex procedure involving the deployment of specialised equipment.

The flushing of umbilicals and hoses is essential to ensure that following manufacturing, any debris or contaminants are completely removed.

Pressure testing is performed in order to ensure the integrity of hoses and umbilicals prior to deployment subsea. Any deformation of the umbilicals resulting from their inability to withstand subsea pressures can have an adverse effect on the performance of the hoses contained inside the umbilicals and the umbilicals themselves.

Aberdeen-headquartered Proserv is one of the industry’s leading experts in flushing and hydrostatic pressure testing services, constructing and supplying pre-fabricated and purpose built rigs to hose and umbilical manufacturers as well as end-users.

Key to the operation and performance of a flush and test rig is fast and effective filling of the hose or umbilical with fluid and Proserv selected triplex plunger pumps because the design is suited to handling the liquids involved, which can vary from job to job and can be water, water / glycol or hydraulic oil.

The Cat Pumps’ 3507 series pumps chosen also provide the high pressures and flow required, typically around 342 Bar at 30lt/min. This degree of pressure is required in order to circulate the fluid at the required flow rate along hoses and umbilicals, which are typically up to 15km in length.

“When we get an application, we look at the fluid being handled, the flow rate, pressure and from there we will decide on which pump type to use,” reports Mick Woolner, at Proserv’s Great Yarmouth site.

“The big advantage that [these pumps] have is their ability to pump fresh water, so that is one of the main reasons why we specified it for this specific application.

“In earlier days, most of the subsea fluids used for testing were oil-based, which meant that several types of pumps could be used. The change to water or water-based fluids has resulted in a requirement for a pump type that can handle this low lubricity media and provide the high pressure required to fill the umbilical or hose quickly.”

Proserv’s Great Yarmouth, Aberdeen and Newcastle-upon-Tyne branches are the main operations for pressure test and hydraulic flushing equipment, as well as accessories such as valves, pipework, tanks etc for the offshore oil and gas sectors.

The company’s transportable pressure testing and flushing rigs are self contained and include a holding tank, pressure and return filtration and flow indication.

Pressure testing is performed prior to flushing and involves the Cat Pump pre-filling the umbilical or hose with the specified fluid at temperatures varying between ambient and 60ºC at pressures up to 340 bar.

When completely filled, pressure testing can be performed and on completion the umbilical or hose is then flushed with the control fluid which is circulated using the same pump at a set pressure.

The tank feeds the pump through a filter, control valve, temperature gauge and flow meter and then into the umbilical or hose. During the flushing process a sample is taken for analysis to ensure that the fluid meets with the required cleanliness specification.

The fluid is then returned to the skid via a filter, flow meter, temperature gauge and back into the IBC for subsequent reuse.

According to Cat Pumps, Proserv has been using its equipment for several years and the 3507 series is proving effective for handling water-based fluids. The problem with these fluids is that they tend to dry the seals.

However, these pumps incorporate an internal re-circulation of fluid at low pressure to the secondary plunger seals ensuring that they are always cooled and lubricated, which in turn leads to extended operating life.

There is no definitive length of time that the pump is required to operate continuously when flushing, as this is dependent on the length of the umbilical and the levels of cleanliness required.

What is important, said the equipment maker, is that a continuous pulse free flow at high pressure is maintained, and that is what the triplex plunger pumps provide.