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Hydromilling for Process Pipeline Cleaning Operations

Hydro milling of pipe systems can be described as a system designed for the specialised internal cleaning of pipes, process lines, and tubes.

Hydro milling has been widely used in Industrial Cleaning and Pre-commissioning applications for the removal of hard deposits from Steam, Lube oil, Compressor, and Process line systems, as well as tube bundles and vessels for many years.

Hydro milling is often selected and used as a preferred method to remove mill scales, deposits and debris that standard Retro Jetting techniques cannot as effectively remove.

Hydro milling (also known as Aqua Milling) is the most technologically advanced system of cleaning the internal surfaces of pipe spools and small vessels, using high pressure water jets.

Standard Retro Jetting pipe cleaning systems involve a rotating (spinning) or static nozzle, with symmetrical water jet pattern configuration, fixed on the end of a high pressure hose which is 'pulled' into the pipe by the thrust created by rearward facing water jets installed on the nozzle head.

The above type of retrojet nozzle typically sits in the pipe invert removing debris from the lower pipe area, but has little cleaning effect on the upper pipe surfaces in larger pipelines. This can sometimes be overcome by using nozzle centralizing skids in the pipes, but this limits cleaning distance attainable, especially if there are multiple bends in the pipe length.

The Hydro milling method offers a much more technically advanced solution to this problem. The nozzle head, fixed on the end of the high pressure hose is static, the entire length of HP hose itself is then rotated using a Rotating Hose Device (RDR unit). The RDR unit is either hydraulically operated or pneumatically operating rotary device. The RDR unit (a wheeled rotary joint) sits externally from the pipe being cleaned, in such a manner that the rotary device can travel the cleaning distances with the rotating hose length which is inserted into the pipeline opening.

The high pressure swivel installed on the RDR unit allows rotational speeds from as low as 10 rpm up to 300rpm thus cleaning the internal pipe wall in its circumference. The High pressure nozzle head and water jets are specially configured to ensure the nozzle stand-off distance from the pipe internal wall surfaces is kept constant, and the hose rotational speed is set to ensure the optimum water jet dwell time is achieved to clean the hardest scales and debris requiring removal from the pipe surface.

This is achieved by configuring the nozzle inserts so that the jet streams are not in balance, which results in the nozzle being 'unbalanced' i.e. it is pushed onto the pipe sidewall by the extra thrust from the larger water jet inserts placed on one side of the nozzle head only. The nozzle head with the high pressure water jets is therefore always close to the pipe surface, thoroughly cleaning the full internal pipe circumference.

The rotating hose is fed though a roller feed system that is speed adjustable, allowing both forward hose feed and return rates to be set according to cleaning requirements. This advanced feed system is so efficient that it can feed a hose up to 1500 feet (450 meters) into a pipe system, and can pass through multiple bends, dependant on pipe diameter, bend radius, etc. The nozzle is also able to climb vertical pipe sections up to 30 meters in height.

Due to the nature of the above working process, Hydro milling has been utilized alongside Retro Jetting by Major Oil and Gas Companies for commissioning purposes prior to process lines being in service, offering a superior system of cleaning pipelines against standard Retro Jetting procedures.

Hydro milling is effective in pipes of diameter 3" up to 72" and above. Key pipeline configuration and varying elements will determine the type of nozzle selection and the pressure and flow requirements of the Hydro milling High Pressure pump unit.