High pressure clean of subsea structures

Cat Pumps
Cat Pumps
Hi Flow/Hi Pressure ROV system for cleaning marine growth from structures.

When one provider needed to produce such a system quickly, they turned to Cat Pumps as they were the only company that could offer an ATEX Zone 1 pump at short notice to the specification.

There can be few more challenging cleaning processes, nor ones that demand ingenious methods, than that of remote cleaning marine growth from subsea structures such as the legs of offshore platforms. For several years Aberdeen-based HPR UK has provided a one stop shop for ROV’s (Remote Operated Vehicles) and ancillary equipment, experienced pilots and survey engineers to carry out inspection projects where the use of divers could be time and safety prohibitive.

Amongst its range of specialist services are ‘Hi Flo / Hi Pressure’ systems for cleaning marine growth from structures to allow for clear visual inspection (Figure1). Unique to HPR UK, these systems use ROVs which can launch and operate in higher sea state conditions than divers. They can also stay in the water for longer, thereby maximising up-time for the project. Also this means that the company has fewer problems with HSE issues.

Cat Pumps high pressure positive displacement triplex plunger model 6821.

High pressure

Cleaning or blasting marine growth from structures involves the use of high pressure water delivered to the point of application through specially designed lances. These create cavitation in the water flow, with the bubbles resulting from this action exploding onto the marine growth. To be wholly effective, the systems require pumps capable of providing the continuous flow of high pressure water from the platform. A pump type that is best suited for this is the high pressure positive displacement triplex plunger pump.

“Most platforms can give us a safe location for our other electrical pumps,” says HPR UK director Dave Gillies, “but we have had several requests for ATEX Zone 1 & 2 pumping equipment. The most recent one came from a customer for whom we had to building a system into a 10’ x 8’ container against a tight deadline.”

Having a very short time-frame for building and delivering the system, HPR UK turned to Cat Pumps as they were the only company that could offer an ATEX Zone 1 pump at short notice to the specification. The pump supplied was the Cat Pumps high pressure positive displacement triplex plunger model 6821 (Fig.2), a compact pump capable of handling seawater at the required flow rate of 70 litres/min at 200 bar. Along with the pump, the container included an Ex-light and flashing beacon, an ATEX approved electrical control panel for managing the motor thermistor and heater, plus a small air driven reeler for the delivery hose deployment.

“Over the last two years we have found an increasing number of our customers are asking for ATEX pumps and pump packages for use in explosive atmospheres,” says Cat Pumps General Manager Brian Hubbard. “Here at Cat Pumps UK we have developed and tested a full range of PD pumps that meet ATEX Zone 1 and 2 areas. The area in which they operate might be designated hazardous even though our pump may be handling a non-flammable liquid, such as seawater. Equally, just because the pumped fluid may be flammable, this would not automatically create an explosive atmosphere, provided that special consideration is given to the pump construction and installation.”

High specification

Due to their extremely high specification of design and manufacture, standard bareshaft Cat Pumps products require very few modifications to make them suitable for use in ATEX areas. Generally, it is only necessary to minimise the risk of static electricity and to strengthen a few external parts to protect against accidental impact damage. Fundamentally the pumps never get hot enough in normal use to ignite most flammable vapours.

“Using seawater being taken from the platform’s fire water ring main, our ROVs typically work down to depths of 50 m, but we can provide up to 200 m of half-inch hose for the larger systems,” continues Dave Gillies. “The ROVs can be in the water for anything between eight and ten hours cleaning large areas of hulls and intricate areas between risers and conductors. This level of duty requires pumps that can maintain both the required pressure and a constant flow over the period of use, which is why the high pressure triplex plunger pump is specified. For this recent contract, we urgently needed an ATEX pump and we knew that Cat Pumps was the only company that could supply a skid-mounted ATEX approved motor and pump in the time available.”