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High-pressure water jetting is a core technology for cleaning pipes, heat exchangers, reactors, and other equipment in the chemical industry. It is efficient, environmentally friendly, and safe. It uses a high-pressure pump to pressurize water to extremely high pressures (typically 70-280 MPa or higher), forming a high-speed jet through a specially designed nozzle, relying on the impact force and shear force of the water itself, and possibly cavitation effects, to detach, pulverize, and remove various stubborn deposits from the inner walls of the pipes.

The following is a detailed analysis of high-pressure water jetting for chemical pipelines:

I. Core Principles

Water Jet Energy: ? When high-pressure water passes through a nozzle with an extremely small aperture, potential energy is converted into extremely high kinetic energy, forming a water column with powerful impact force.

Impact and Shear: ? The high-speed water flow directly impacts the surface of the fouling, generating a huge impact pressure wave that causes the fouling to break and loosen. At the same time, the water flow generates shear force at the interface between the fouling and the pipe wall, peeling off the fouling.

Water Wedge Effect: ? Water flow penetrates into the micro-cracks of the fouling or the gaps with the pipe wall, producing a wedge-like effect that accelerates the detachment of the fouling.

Cavitation Effect (more significant at high pressure): ? Tiny bubbles generated in the water flow collapse instantly near the surface of the fouling, producing local high pressure and micro-jets, which have a good pulverizing effect on brittle fouling.

Fluid Transport: ? The detached fouling fragments are carried away by the subsequent water flow and discharged from the pipeline.

II. Main Advantages (especially in the chemical field)

Highly Efficient and Thorough: ? It can effectively remove various hard scales (such as polymer coking, catalyst powder, inorganic salt scaling, carbon deposits), soft scales (such as oil sludge, viscous residues), and even some coatings.

Safe and Environmentally Friendly:

No Chemical Reagents: ? Avoids the use of hazardous chemicals, eliminating the risks and environmental pollution associated with chemical cleaning, storage, use, and waste liquid treatment.

No Sparks: ? Pure water operation, inherently safe, especially suitable for flammable, explosive, and toxic chemical environments (such as oil and gas, petrochemicals, coal chemicals).

Easy Waste Disposal: ? The waste generated is mainly water and solid residue, which is easier to separate and treat than chemical waste liquid.

Non-destructive to Base Material: ? By selecting the appropriate pressure and nozzle, fouling can be effectively removed without damaging the metal pipe body (carbon steel, stainless steel, alloys, etc.).

Wide Range of Applications: ? Suitable for various pipe diameters (from capillaries to large-diameter pipelines), complex shapes (elbows, tees, U-tubes), long-distance pipelines, and sensitive equipment.

Potential for Online Cleaning: ? In some cases, local isolation online cleaning can be achieved to reduce downtime.

High Cleanliness: ? Can achieve very high cleanliness standards to meet the requirements of subsequent processes (such as catalyst loading, product purity).

III. Detailed Cleaning Process

Preliminary Preparation and Safety Assessment:

Risk Assessment: ? Identify risks such as chemical residue, confined spaces, high-pressure water jets, noise, and slips, and develop contingency plans (rinsing water, first-aid points).

Personnel Protection: ? Operators must wear a complete set of qualified PPE: High-pressure water-resistant chemical protective clothing (Type 5/6), full-face mask (with hearing protection), puncture-resistant and anti-slip safety boots, heavy-duty cut-resistant gloves.

Equipment Inspection: ? Check that the high-pressure pump, hoses, gun rods, nozzles, joints, safety valves, and pressure relief devices are in good condition, and that the pressure gauge calibration is valid.

Wastewater and Waste Residue Collection: ? Set up an effective wastewater and waste residue collection system (such as a dike, vacuum suction equipment) to prevent secondary pollution.

Pretreatment:

For particularly viscous or hardened fouling, low-pressure hot water rinsing or chemical soaking may be used to soften it (safety and necessity must be assessed).

Equipment Connection and Parameter Setting:

Connect the high-pressure pump water source (usually clean industrial water) to the system.

According to pipe material, inner diameter, fouling type, thickness, and hardness , select the appropriate:

Working Pressure: ? (Key!)

70-140 MPa: Removes soft scales, oil sludge, and general deposits.

140-250 MPa: Removes moderately hard scales (such as carbonates, sulfates, some polymers).

250-280+ MPa: Removes extremely hard scales (such as sintered coking, hard polymers, catalyst hard blocks).

Flow Rate: ? (In synergy with pressure) Typically 20-100 L/min or higher. High flow rates provide stronger scouring and debris removal capabilities, especially important for large-diameter and long-distance pipelines.

Nozzles:

Type: ? Front nozzles (straight-in cleaning), rotating nozzles (360° coverage, high efficiency), fan nozzles (surface cleaning), self-propelled nozzles (automatic advancement in long straight pipelines).

Aperture and Quantity: ? Determine the final jet velocity and impact force. Small apertures produce higher speeds, and multiple nozzles increase coverage area.

Connect the high-pressure hose, lance (rigid rod or flexible hose), and selected nozzle.

Carefully insert the nozzle (usually connected to a rigid rod or hose) into the pipe inlet.

Cleaning Operation:

Advancement Method:

Manual Push and Pull: ? Suitable for short distances, large diameters, or accessible straight pipe sections. The operator holds the rigid rod or hose and slowly, steadily pushes and pulls it through the pipe.

Automatic Advancement System: ? Used for long-distance (tens to hundreds of meters) pipelines. It utilizes the reaction force of the water jet or an external traction device (such as a winch) to drive the nozzle automatically forward and backward in the pipe. This is the standard method for cleaning long pipelines.

Cleaning Mode:

Targeted Cleaning: ? Concentrated cleaning on key fouling areas (such as bends, welds, and diameter changes).

Continuous Scanning: ? The nozzle continuously rotates and jets during the advancement/retraction process, covering the entire pipe wall.

Travel Speed: ? Adjust in real-time according to the fouling removal situation. Too fast a speed will result in incomplete cleaning, while too slow a speed will reduce efficiency and may damage the pipe wall.

Debris Observation: ? Closely observe the color, turbidity, and presence of large debris in the outlet water flow to judge the cleaning effect.

IV. Key Equipment

High-Pressure Plunger Pump: ? The core power source, providing a stable high-pressure water flow. Key parameters: pressure, flow rate, power.

High-Pressure Hose: ? Transports high-pressure water; it must be high-pressure resistant, wear-resistant, and flexible. Available in different pressure ratings and lengths.

Spray Gun/Lance:

Rigid Spray Gun: ? Metal rod, used for cleaning short-distance, straight-through pipelines; direct operation.

Flexible Spray Gun: ? Made of high-strength steel wire-wrapped hose, it is bendable and used for pipelines with complex routes or those requiring bypassing obstacles.

Nozzles: ? The core working component, determining the jet shape and performance. The material is super-hard alloy (tungsten carbide, diamond, etc.).

Nozzle: ? A device that installs multiple nozzles; common types include fixed and rotating types.

Automatic Advancer/Reel: ? Used for long-distance pipeline cleaning, automatically retracting the hose or driving the nozzle.

Safety Devices: ? Pressure control valve, safety relief valve, emergency stop switch, lance safety locking device, etc.

Water Treatment Unit (Optional): ? Filters and softens the water source, reducing nozzle wear and system clogging.

Wastewater Recycling System: ? Vacuum trucks, cofferdams, separation tanks, etc., used for collecting and preliminary treatment of wastewater and waste residue.

Detection Equipment: ? Pipeline borescope, pressure gauge, etc.

V. Safety Precautions (Extremely Important!)

High-Pressure Water Jet Hazards: ? High-pressure water jets have extremely strong penetrating power and can cause serious lacerations, penetrating wounds, tissue tearing, and even amputation. 。 Strictly prohibit any part of the body from contacting the jet! ? Strictly adhere to the prescribed safety distance.

Chemical Residue Risk: ? Even after purging, toxic and harmful substances may still remain in the pipeline. Conduct strict gas detection (combustible gases, toxic gases, oxygen content); entry into confined spaces must comply with permit procedures.

Confined Space Risk: ? Pipelines, manholes, etc., are confined spaces and have risks of hypoxia, hyperoxia, and toxic gas accumulation. Forced ventilation and continuous monitoring are crucial.

Noise: ? High-pressure pumps and jets produce tremendous noise (>85 dB); effective hearing protection must be worn.

Slips/Trips: ? The work area is wet and slippery, and high-pressure hoses may also become obstacles. Keep the work area clean.

Equipment Integrity: ? Regularly inspect and maintain all high-pressure equipment, especially hoses, joints, and protective devices. Do not use defective equipment.

Training and Qualifications: ? Operators must receive strict professional training and obtain the corresponding qualifications, being familiar with equipment operation, risk identification, and emergency response.

Work Permit: ? Strictly enforce the work permit system.

Communication and Warning: ? Set up clear warning signs in the work area and ensure smooth communication between operators (using gestures or walkie-talkies).

VI. Common Problems and Countermeasures

Incomplete Cleaning:

Reasons: ? Insufficient pressure/flow; improper or worn nozzle selection; excessive travel speed; special nature of fouling (such as elastic polymers).

Countermeasures: ? Optimize cleaning parameters; replace suitable or new nozzles; reduce travel speed; consider pretreatment (such as hot soaking) or change cleaning methods (such as PIG cleaning + water jet).

Nozzle Clogging:

Reasons: ? Many impurities in the water source; fouling debris is too large; foreign objects in the system.

Countermeasures: ? Strengthen water source filtration; use larger aperture nozzles or rotating self-cleaning nozzles; thoroughly purge the system; install filters.

Hose/Joint Leakage or Rupture:

Reasons: ? Wear and tear; exceeding rated pressure; improper connection; external force damage.

Countermeasures: ? Regularly check and replace; strictly prohibit overpressure; connect and tighten correctly; avoid excessive bending or crushing of hoses; use protective sleeves.

Excessive Recoil:

Reasons: ? Excessive pressure/flow; improper operation (such as sudden opening).

Countermeasures: ? The operator should stand firmly, hold the spray gun with both hands; use a spray gun with a support bracket or automatic equipment; open the valve smoothly; appropriately reduce pressure/flow.

Pipe Damage:

Reasons: ? Excessive pressure; nozzle too close to the pipe wall; prolonged stay at weak points (such as welds, corrosion points); unsuitable material (such as soft metal, lining).

Countermeasures: ? Strictly control pressure according to pipe material and condition; maintain a reasonable spraying distance; avoid staying at weak points; assess pipe condition before cleaning.

VII. Application Scope

Remove coking, polymers, catalysts, salt scales, oil sludge, etc., from reactors, polymerization kettles, distillation column trays and downcomers, and heat exchanger tubes/shell sides.

Clean process pipelines that transport various chemical raw materials, intermediates, and products.

Ash and scale removal from boiler water wall tubes, economizer tubes, and air preheaters.

Cleaning storage tanks (requires special equipment and methods).

Pretreatment of surfaces (such as before coating, before lining).

Summary:

High-pressure water cleaning is an indispensable efficient, safe, and environmentally friendly technology for the maintenance of chemical pipelines. Its successful implementation depends on accurate assessment of fouling and pipeline conditions, appropriate equipment selection (especially pressure and nozzles), strict and standardized operating procedures, and absolutely prioritized safety management The professional skills of operators and their respect for safety risks are crucial. Compared with chemical cleaning and mechanical cleaning (such as drill rods), high-pressure water cleaning has significant advantages in the chemical industry, especially in handling flammable and explosive media residues and pursuing environmental benefits.