During long-term operation, industrial equipment — affected by water quality, media, temperature, and pressure factors — gradually accumulates various types of fouling on heat exchange surfaces, pipeline inner walls, and vessel surfaces: water scale, rust deposits, oil coke, polymer crystals, and microbial slime. These deposits not only reduce heat transfer efficiency and increase energy consumption, but in severe cases can trigger under-deposit corrosion and even equipment perforation and leakage. According to statistics, industrialized countries suffer economic losses from fouling amounting to approximately 0.25% of GDP annually, with energy waste from heat exchange equipment fouling being particularly staggering. Selecting the appropriate cleaning technology is a critical step in maintaining equipment performance and extending service life. This article systematically overviews the mainstream industrial equipment cleaning methods and their application scenarios, from chemical cleaning and high-pressure water jetting to emerging technologies such as dry ice blasting and ultrasonic cleaning.

1. Chemical Cleaning: Penetrating Every Inch of Metal Surface

Chemical Cleaning utilizes chemical reactions — dissolution, complexation, oxidation — between chemical agents and fouling to convert deposits into soluble substances that are then discharged with the circulating solution. Its greatest advantage is that liquids can penetrate dead zones inaccessible to mechanical tools: tube bundle gaps, weld roots, baffle plate backsides, and other areas where dense hard scale removal is particularly effective. Chemical cleaning can be divided into the following three categories based on the agent system:

Acid Cleaning is the most commonly used chemical cleaning method. Strong inorganic acids such as hydrochloric acid (HCl) rapidly dissolve carbonate water scale and rust, per the reaction: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑. For silicate scale, hydrofluoric acid (HF) is required to react with SiO₂ to generate gaseous SiF₄. Organic acids such as Citric Acid and Sulfamic Acid are mild, and when used with corrosion inhibitors can significantly reduce corrosion risk to metal substrates — particularly suitable for precision cleaning of stainless steel equipment. The standard acid cleaning procedure includes six stages: water flush → alkaline degreasing → acid descaling → rinse → passivation → inspection and acceptance, with the entire cycle typically lasting 1–2 days.

Alkaline Cleaning is primarily used for degreasing. NaOH solution under heated conditions saponifies animal and vegetable oils into water-soluble sodium fatty acid salts and glycerol; combined with surfactants, it achieves emulsification and dispersion stripping of mineral oils. Alkaline cleaning is an essential pre-commissioning step for new installations — anti-rust oil and cutting fluid residues on new equipment inner walls must be thoroughly removed, otherwise they become "seed" points for scale growth during subsequent operation.

Complexometric Cleaning, represented by EDTA, forms stable chelates with Ca²⁺, Mg²⁺, and Fe³⁺ under mildly alkaline conditions, achieving "acid-free" descaling. Because the cleaning solution pH is near neutral with virtually no corrosion, EDTA cleaning is widely used in nuclear power plant steam generators, food-grade stainless steel equipment, and other scenarios with extremely high safety requirements. The drawback is higher chemical costs compared to conventional acid cleaning.

The core safety measure in chemical cleaning lies in the scientific application of corrosion inhibitors. Urotropine, Benzotriazole (BTA), Sodium Molybdate, and other inhibitors form molecular-level protective layers on metal surfaces through physical adsorption or chemical film formation, reducing corrosion rates by over 99% and enabling acid cleaning to proceed safely under the principle of "removing scale without damaging the substrate."

2. High-Pressure Water Jetting: Shattering Stubborn Scale with Hydraulic Force

High-Pressure Water Jetting uses water as the medium, pressurizing it to 500–3,000 bar through high-pressure pumps and forming high-velocity jets through specialized nozzles. The kinetic energy of the water impact strips scale, rust, and old coatings from equipment surfaces. Its essence is the conversion of pressure energy into kinetic energy — when the jet impact force exceeds the bond strength between fouling and substrate, the scale layer fractures and is carried away with the water flow.

The core equipment for high-pressure water jetting includes diesel or electric motor-driven high-pressure plunger pumps, ultra-high-pressure hoses, foot pedal valves (safety control), and various specialized nozzles. Nozzle selection determines cleaning effectiveness: straight nozzles have strong penetration, suitable for clearing completely blocked pipes; rotating nozzles cover large areas, using centrifugal force to sweep the jet in a spiral trajectory across tube walls — the primary tool for heat exchanger tube bundle cleaning; 3D rotating nozzles can spray simultaneously forward and radially, used for comprehensive cleaning of storage tank and reactor inner walls.

The standout advantage of this technology is that it requires no chemical agents — the wastewater consists only of clean water and stripped scale debris, making it environmentally friendly with no corrosion risk. For severely fouled equipment with scale layers exceeding 3 mm thickness, high-pressure water jetting delivers rapid "forceful demolition"-style cleaning — for example, a heavily scaled shell-and-tube heat exchanger can have all tube bundles restored to patency within hours using 1,500 bar high-pressure water tube-by-tube. However, its limitations are also evident: for equipment with densely packed tube bundles (tube spacing less than 5 mm), extremely small tube diameters (below φ10 mm), or excessive bends, the nozzles cannot reach all areas. Furthermore, high-pressure water poses serious safety risks to operators — jets above 1,500 bar can penetrate skin and protective clothing, requiring operation exclusively by certified professionals strictly following safety protocols.

3. Dry Ice Blasting: Residue-Free "Sublimation" Cleaning

Dry Ice Blasting uses solid carbon dioxide particles (-78.5°C) as the cleaning medium, accelerated by compressed air to supersonic speeds and projected onto fouled surfaces. The cleaning mechanism involves three effects: cryogenic shock causing rapid cooling and embrittlement of the scale layer, producing micro-cracks; kinetic impact from dry ice particles propagating cracks to detach the scale layer; and the "micro-explosion" effect when dry ice penetrates scale layer crevices and instantly sublimates (volume expansion approximately 800×), thoroughly stripping residues from the substrate surface — while the dry ice itself completely sublimates into CO₂ gas, leaving zero secondary waste.

The defining characteristics of dry ice blasting are "dry" and "residue-free" — no water used, no chemical agents introduced, no wastewater generated, with equipment ready for immediate use after cleaning without drying. These properties make it irreplaceable in the following scenarios: electrical cabinet and motor winding cleaning (avoiding short circuits from water and chemicals), food production line cleaning (no chemical residue risk), precision mold online cleaning (no shutdown, no disassembly), and smoke stain removal from historical artifacts and building surfaces. The limitations of dry ice blasting include low efficiency for thick hard scale layers (exceeding 2 mm), high equipment operating noise (requiring hearing protection), and stringent storage and transportation requirements for dry ice pellets — dry ice continuously sublimes at ambient temperature and must be used within 24–48 hours of procurement.

4. Ultrasonic Cleaning: Micro-Purification of Precision Components

Ultrasonic Cleaning utilizes the "cavitation effect" generated by ultrasound in liquid — high-frequency sound waves (typically 20–80 kHz) create alternating positive and negative pressures within the cleaning solution. In negative pressure zones, the liquid is stretched to form micron-scale bubbles, which collapse violently during positive pressure transients, releasing localized micro-jet shockwaves with temperatures reaching thousands of degrees Celsius and pressures of hundreds of atmospheres. These shockwaves strip microscopic particles, oil films, and oxide layers from workpiece surfaces. Thousands of bubbles cavitating simultaneously is equivalent to countless miniature high-pressure water guns acting on the workpiece surface.

Ultrasonic cleaning achieves micron-level precision, capable of removing contaminants from blind holes, cross-holes, and narrow slits inaccessible to conventional methods, making it widely applied in precision manufacturing: automotive engine injectors, hydraulic valve bodies, medical devices, semiconductor wafer carriers, and watch components all depend on ultrasonic technology. In industrial equipment maintenance, ultrasonic cleaning is primarily used for small removable components — such as heat exchanger gasket grooves, instrument probes, filter elements, and valve assemblies — for deep purification. Its limitations include the cleaning tank dimensions restricting workpiece size (large equipment cannot be directly immersed), and limited efficiency for high-viscosity oil coke and thick hard scale, typically requiring heated chemical cleaning solutions for combined use.

5. Sandblasting and Shot Blasting: The "Rebirth" of Metal Surfaces

Sandblasting and Shot Blasting both belong to mechanical impact cleaning, removing rust, mill scale, old paint films, and welding spatter by high-velocity projection of solid abrasives onto metal surfaces. Sandblasting uses compressed air to accelerate abrasives such as quartz sand, steel grit, or corundum to 60–100 m/s for projection onto workpiece surfaces, suitable for irregularly shaped large structural components — such as storage tank interior and exterior walls, steel structure platforms, ship hulls, and bridges. Shot blasting uses high-speed rotating impellers to hurl steel shot with greater impact force and better uniformity, primarily for batch processing of regular workpieces — such as steel pipe interior and exterior walls, steel plate pretreatment lines, and casting cleaning.

These two technologies are not only cleaning methods but also important components of surface treatment processes — post-sandblasting metal surfaces can achieve Sa 2.5 (near-white) cleanliness and 50–75 μm roughness, providing an ideal anchor profile for subsequent coating. In industrial equipment maintenance, sandblasting/shot blasting is commonly used for heat exchanger head interior rust removal, reactor jacket exterior refurbishment, and surface pretreatment before pipeline external corrosion protection coating repair. The drawbacks include generation of substantial dust and waste abrasive, requiring dust collection and recovery systems, and the need for masking protection on precision mating surfaces and soft metals to prevent dimensional damage.

6. Technology Selection and Combination Strategies

No single cleaning technology is the "optimal solution" — in actual engineering, effective cleaning approaches are often synergistic combinations of multiple technologies:

"Hydraulic Clearance + Chemical Precision Cleaning": For heat exchangers with extensively blocked tube bundles, first use high-pressure water jetting to rapidly clear 70%–80% of blocked tubes, opening flow paths before following with chemical circulation cleaning to dissolve the remaining 20%–30% of stubborn hard scale. This combination can reduce total construction duration by over 40% and halve chemical consumption, making it the standard operating mode for large heat exchanger cleaning projects.

"Chemical Soak + High-Pressure Flushing": For reactors and digesters with silicate mixed scale, first use HF-based cleaning solution to soak and soften silicate scale for 4–6 hours, then strip the loosened scale with high-pressure water jetting — efficiency far exceeds single-technology approaches.

"Dry Ice Pre-Cleaning + Ultrasonic Precision Cleaning": For precision molds and valve body assemblies, first remove surface oil and release agent residues with dry ice blasting, then place in ultrasonic cleaning tank for micron-level deep purification — two complementary processes delivering both efficiency and thoroughness.

Selection decisions must comprehensively consider five dimensions: scale layer type and thickness, equipment material and structure, site construction conditions, environmental discharge requirements, and economic budget. A principle worth remembering: any cleaning plan must undergo small-sample testing before full-scale construction — trial cleaning on a non-critical area of the same equipment to verify cleaning effectiveness and material compatibility, confirming parameters before full deployment.

7. Safety and Environmental Protection: Non-Negotiable Bottom Lines

Regardless of which cleaning technology is employed, safety and environmental protection are non-negotiable bottom lines. Chemical cleaning requires strict management of acidic waste liquid neutralization treatment and heavy metal precipitation removal — waste liquid pH and heavy metal content must meet standards before discharge. High-pressure water jetting operators must hold certification and wear cut-resistant protective gear, with warning lines and emergency stop devices established in the work zone. Dry ice blasting sites require adequate ventilation to prevent CO₂ accumulation. Sandblasting operations must be equipped with positive-pressure supplied-air respiratory protection and high-efficiency dust collection systems.

As environmental regulations tighten and corporate ESG requirements rise, the "green cleaning" philosophy is driving industry transformation: biodegradable Citric Acid formulations are progressively replacing strong inorganic acids; high-pressure water jetting is evolving toward ultra-high pressure (above 3,000 bar) and automation to reduce human exposure; dry ice blasting is expanding from food and electronics sectors into general industrial applications; and research and application of online cleaning technologies (no equipment disassembly, no shutdown) is accelerating. The future of industrial cleaning will no longer be merely an auxiliary maintenance process but a systems engineering discipline integrating chemical engineering, fluid mechanics, materials science, and automation control.

Danyang Blue Star Cleaning has cultivated deep expertise in the industrial equipment cleaning field for over 20 years, possessing complete construction capabilities and professional qualifications in chemical cleaning, high-pressure water jetting, and dry ice blasting. We can develop "one-machine, one-plan" combined cleaning processes based on equipment materials, scale characteristics, and site conditions. For technical consultation or equipment cleaning services, please call: 18952832843.

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