NCCER Hydroblasting flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Injection injury

A high-pressure water jet can penetrate skin at pressures as low as 100 psi, causing deep tissue damage; requires immediate medical treatment even if the wound looks minor.

Reaction force formula

Reaction force (lbf) on a straight nozzle ≈ 0.0526 × flow (gpm) × √(pressure in psi). Example: 10 gpm at 10,000 psi gives about 52.6 lbf.

Water jet velocity

Velocity (ft/s) ≈ 12.4 × √(pressure in psi / fluid density in lb/ft³). For water at 10,000 psi, velocity is about 1,240 ft/s.

Noise hazard

Hydroblasting often produces noise above 100 dBA. Use dual hearing protection (earplugs plus earmuffs) when levels exceed 100 dBA.

Minimum PPE

Impact-rated face shield over safety glasses, hard hat, heavy waterproof gloves, steel-toe boots, and waterproof suit. Never wear loose clothing near rotating equipment.

Hose inspection

Inspect hoses before each use for cuts, bulges, or exposed wire. Tag defective hoses out of service; use a 4:1 safety factor for restraints.

Confined space testing

Before entry, test atmosphere: oxygen 19.5–23.5%, LEL below 10%, H2S below 10 ppm, CO below 35 ppm. A standby attendant with retrieval system is required.

Triplex pump power

Brake horsepower (bhp) ≈ (flow in gpm × pressure in psi) / (1714 × pump efficiency). Efficiency is typically 0.85–0.95.

Nozzle orifice size

Nozzle size number equals flow in gpm at 4,000 psi. Flow at other pressures = size × √(pressure/4000). Example: size 4 at 10,000 psi flows about 6.3 gpm.

Fan vs rotating nozzle

Fan nozzles produce a flat spray for surface cleaning. Rotating (turbo) nozzles increase impact for pipe and tube cleaning.

Hose burst rating

High-pressure hoses are rated by burst pressure, typically 4:1 over working pressure. Observe minimum bend radius and temperature limits marked on the hose.

Accumulator precharge

Accumulators dampen pressure pulsations and protect the pump. Precharge pressure is typically 60–80% of operating pressure.

Relief valve setting

Safety relief valves must be set at or below the pump's rated working pressure and tested regularly. Never plug or disable a relief valve.

Deadman control

A foot pedal or remote control valve allows the operator to depressurize the lance instantly. Deadman controls are required for safe operation.

Pre-start checks

Before start-up, confirm connections are tight, hoses restrained, relief valve functional, and all personnel clear of the nozzle path.

Start-up procedure

Start the pump at low pressure, then gradually increase to working pressure while monitoring gauges and listening for cavitation or knocking.

Lance length

Use a lance with a minimum length of 4 feet for hand-held operations. Keep both hands on the lance and maintain a stable stance.

Pipe cleaning technique

Use a back-out or rotating nozzle and control insertion rate. Never exceed the hose manufacturer's recommended pull force.

Shutdown sequence

Reduce pressure to zero, stop pump, lock out/tag out, bleed residual pressure, and secure the lance before disconnecting hoses.

Cold weather care

Drain hoses and pump after use to prevent freezing. Store hoses coiled at a diameter larger than the minimum bend radius.

Communication

Use hand signals or radios. The pump operator must maintain visual contact with the nozzle operator or have a dedicated signal person.

Concrete removal pressure

Pressures of 10,000–20,000 psi are typical for concrete removal. Paint removal may require 3,000–10,000 psi depending on coating adhesion.

Standoff distance

Closer standoff increases impact but reduces coverage. Typical standoff is 6–12 inches for fan nozzles.

Traverse rate

Slower movement increases cleaning but may damage substrate. Test on a small area to determine optimal rate.

Nozzle selection

Use fan nozzles for broad surfaces and rotating nozzles for pipes, tubes, and heat exchanger bundles.

Post-cleaning inspection

After cleaning, inspect surface for remaining coating or damage. Use a profile gauge or visual comparator to verify cleanliness.

Wastewater containment

Wastewater from hydroblasting may contain contaminants. Contain and dispose of according to environmental regulations.

Daily inspection

Check hoses for cuts, bulges, or abrasion; check nozzles for wear or blockage; inspect couplings and fittings for leaks.

Pump maintenance

Check oil level and condition, packing or plunger wear, and valve condition. Change oil per manufacturer's interval.

Nozzle wear

Replace nozzles when flow increases more than 10% above rated or spray pattern becomes uneven. Worn nozzles reduce impact.

Low pressure troubleshooting

Check relief valve, worn nozzle, or pump internal leak. Pulsation may indicate accumulator precharge loss or valve wear.

Hose failure signs

Pinhole leaks, bulging, or exposed wire indicate hose failure. Remove from service immediately and tag.

Maintenance log

Record inspections and maintenance in a log. Include date, equipment ID, findings, and corrective actions.