Technical guidance on deposits, surfaces and washwater
High Pressure Jetting Methods and Applications
High pressure jetting uses a directed water jet to loosen or remove material from a pipe, vessel or surface. The suitable method depends on the deposit and the material beneath it. Pressure is one part of the specification; access, water flow, jet arrangement, recovery and the required finished condition also matter.
Silt, mineral scale, roots, coatings and process residues behave differently. Loose sediment may need mobilisation and recovery, while a strongly attached deposit can require a different approach. An unknown residue needs identification before assumptions are made about how it will respond to water.
The pipe or surface must be considered alongside the deposit. Material, wall condition, linings, coatings, earlier repairs and vulnerable fittings can limit the available method. A clean-looking surface is not a useful result if the underlying asset has been damaged.
A cleaning objective that can be checked
The intended result may be restored passage, removal of a particular deposit, access for an inspection or preparation for a later coating. Those are different objectives. The work description should make the required extent and finish clear enough to assess afterwards.
Before-and-after inspection can show the accessible condition, but it does not establish every hidden defect. For a drainage run, remaining sediment, open connections and visible pipe defects are relevant. For a prepared surface, the acceptance criteria come from the next operation and the asset specification.
Access and the work area
Pipe length and diameter, available openings, bends and the distance from the equipment affect how the jetting head can reach the deposit. A vessel has different access and isolation arrangements from an open pavement. The same material can therefore need a different cleaning setup in two installations.
Work on plant has to fit the maintenance arrangements for that plant. The HSE guidance on maintenance of work equipment explains the importance of planning and suitable isolation. Those controls are part of the job assessment rather than evidence that a particular cleaning technique is suitable.
Recovering what the water removes
Loosened material remains part of the job. Moving silt down a drain can leave it at the next restriction; washing contamination from a surface can transfer it into runoff. The recovery method therefore needs to be considered with the cleaning method.
The amount and character of the washwater affect containment, separation and the route for treatment or disposal. For sites in England, the Environment Agency pollution-prevention guidance explains how drainage routes and potentially contaminated water should be managed. Surface-water drains, foul sewers and controlled waters have different requirements. Cleaning a drain does not itself authorise a discharge into it.
Using the library for a particular deposit
The existing guides below separate mineral scale, concrete ingress, roots, silt and coating removal. They explain which asset information is useful and where cleaning needs to be distinguished from repair. A deposit name alone does not choose the equipment or establish a finished-work standard.
For example, root removal can expose an entry defect that needs a separate repair. Silt and grit recovery focuses on taking material out of the system. Keeping those objectives distinct makes the work easier to specify and the result easier to assess.
Water jetting can remove coatings from steel, but the required surface condition, the steel itself and the route for residues and washwater all need to be defined.
Water jetting has specialist applications in casting cleaning. The casting material, the residue to be removed and the required finish determine whether the process is suitable.
Technical notes
Casting: material, dimensions and surfaces that must be protected.
Residue: type, location and how firmly it is attached.
Finish: the dimensional or surface requirement after cleaning.
Water jetting can be used to prepare concrete surfaces. The existing concrete, the material to be removed and the specification for the next operation define the required finish.
Technical notes
Concrete: condition, repairs and any areas that must not be removed.
Preparation objective: contamination or coating removal, or removal of concrete itself.
Finished condition: the surface requirement for the next coating, repair or construction stage.
Hydrodemolition uses high-pressure water to remove concrete. The engineering specification needs to define the area and depth of removal, what must remain and the required condition of the exposed surface.
Technical notes
Removal limits: area, depth and concrete that must remain.
Structure: condition of the concrete and any reinforcement or features that must be protected.
Finished surface: the engineering requirement after removal.
Water jetting has specialist deburring and deflashing applications. Part material, the burr or flash and the dimensional or surface requirement determine process suitability.
Technical notes
Part: material, dimensions and features that must not be damaged.
Burr or flash: size, location and production process.
Finished condition: dimensional and surface requirements after removal.
Water jetting is used to remove paint-booth build-up. The coating, booth surfaces, nearby equipment and the way residues and washwater will be contained all affect the method.
Technical notes
Build-up: coating type, thickness and any available product information.
Surfaces and equipment: materials that must remain undamaged and anything nearby that needs protection.
Containment: how paint residues and washwater will be collected.
Water jetting is used to remove pavement markings and runway rubber. Pavement type, the material being removed and the finish required afterwards determine whether it suits the area.
Technical notes
Surface: asphalt, concrete or other pavement construction and its condition.
Material to remove: marking, coating or rubber build-up and the area involved.
Finish and recovery: the condition required afterwards and how water and debris will be collected.
Water jetting can be used to strip coatings from pool surfaces. Pool construction, the existing coating and the finish needed for the next treatment define the cleaning objective.
Technical notes
Pool surface: construction material, condition and any repairs.
Coating: type, condition and any available product information.
Required finish: what the next coating or repair specification calls for.
