Reactor Cleaning Procedure: An 8-Step Route from Shutdown Isolation to Passivation Acceptance

Abstract:Reactor cleaning runs in eight steps - shutdown and displacement, isolation, confined space entry, deposit identification, process selection, circulation set-up, cleaning control, waste liquor handling, passivation and acceptance. The governing rule is to identify the deposit before choosing the route: carbonate scale is removed by circulating LX-903 compound cleaner (sulphamic acid type), oil and organic fouling is stripped first with LX-902 compound cleaner, and tar or polymer is soaked with LX-901 compound cleaner. Fluoride systems are excluded on enamel reactors and chloride is controlled throughout on stainless steel. Cleaning quality is judged under GB/T 25146-2010 and HG/T 2387, and water jetting inside the vessel follows GB/T 26148-2025.

1. Scope and Preconditions

This procedure covers enamel, stainless steel and carbon steel reactors in chemical, pharmaceutical, fine chemical and food plants, including the vessel wall, agitator and shaft, internal coils, jacket and outlet valve group, cleaned by chemical methods and high-pressure water jetting. Where the vessel is a fixed pressure vessel, cleaning must not start without an approved procedure stating the cleaning medium, temperature, liquid level and pressure limit; on jacketed or coil-fitted reactors the jacket and the vessel interior are run as separate circuits and are never connected in series.

The three material groups behave differently. On enamel, inspect the glass lining first: spalled areas cannot take a high-velocity jet and fluoride systems are excluded. On stainless steel, check grade and chloride: 304 and 316L pit and stress-crack in chloride media, so both the cleaning liquor and the rinse water are controlled. On carbon steel, check the corrosion allowance: acid cleaning requires an inhibitor and coupon verification, and neither temperature nor concentration may be raised by feel.

Assemble the documents before start-up: equipment data (volume, material, heat transfer area), the previous cleaning record and chemical system used, the process medium and scaling cycle, and photographs of the deposit sample. Where records are missing, sample first and decide the route afterwards.

2. Steps 1-3: Shutdown, Isolation and Confined Space Entry

Step 1, shutdown: cool down, depressurise and drain the product, then displace according to the medium. Flammable media are displaced with nitrogen or steam, acid and alkaline media with water until near neutral, and toxic media are checked for residue after displacement. Cooling is gradual, and on enamel reactors cold liquid must never enter a hot vessel.

Step 2, isolation: blank off between jacket and interior, disconnect or blind every connected line, lock out the agitator motor, and secure the agitator in the maintenance position so it cannot turn or drop onto the lining during cleaning.

Step 3, confined space entry: work inside the vessel is confined space work and requires a permit, a dedicated attendant and continuous mechanical ventilation, with oxygen and flammable gas monitored. Typical control values are 19.5-21% oxygen and flammable gas below 10% of the lower explosive limit, with the actual figures taken from site measurement and the company permit. Use safety extra-low voltage lighting, and no metal tools are struck against an enamel lining.

3. Step 4: Deposit Identification and Process Selection

Where the sample is taken decides whether the judgement is right: mid and lower vessel wall, outside of the internal coil, root of the agitator, and the outlet. These four places often carry different deposits - the coil outside is usually hard scale, the upper wall carries build-up and polymer, and the outlet collects slime.

Identify by looking and testing: colour and layer structure first; a few drops of dilute acid to see whether it effervesces (carbonate scale effervesces, iron oxide dissolves to a yellow-brown); alkali to test emulsification (oil and organics); solvent to test dissolution (tar and polymer). Mixed deposits are treated by defining one main route for the dominant type plus a single auxiliary step, rather than running two processes at once.

Three material limits belong in the written procedure: fluoride systems are excluded on enamel reactors because HF and fluorides attack the glass lining; chloride in the cleaning liquor and rinse water on stainless steel is set from the equipment technical file, capped at 25 mg/L in the cleaning liquor where stainless steel is present (GB/T 25146-2010 clause 5.2.9), and set conservatively where no file exists; carbon steel acid cleaning carries an inhibitor and same-material coupons for the corrosion rate check.

4. Step 5: Circulation Set-up and Temperature Control

Circuit design: a temporary circulation pump, mixing tank, filter and temporary piping form the loop, with the feed at the lower part of the vessel and the return at the upper overflow level. The jacket is a separate circuit and is not cleaned at the same time as the interior, so that pressure cannot cross over.

Heating and temperature: the alkaline wash temperature follows the material and deposit type - 60-80 C for enamel reactors and heat-sensitive deposits, rising to 80-100 C for 4-8 hours where stainless or carbon steel carries heavy oil fouling, with the cleaning liquor capped at 80 C on glass-lined vessels; the acid clean normally runs at 50-60 C for 4-6 hours and at ambient for light scale, with the heating rate held below 20 C per hour (industry practice, finally fixed by the bench test on the deposit sample and the site conditions). Enamel reactors are heated and cooled more slowly, and the temperature probe sits below the liquid surface with a second point for cross-checking.

Safety fittings: level gauge and overflow on the mixing tank, a vent at the high point of the loop, supports and tagging on temporary piping, earth leakage protection on the distribution box, and equipotential bonding between pump and vessel. The vessel must not be pressurised during cleaning, and the loop is isolated from the relief valve and rupture disc.

5. Step 6: Cleaning and Process Control

The main sequence runs: water flush (loose deposit and residue) - alkaline wash (optional, for oil and organics) - intermediate water flush - acid clean (hard scale) - displacement and neutralisation - passivation - rinse to neutral. Each step is sampled and confirmed before the next begins; the sequence is not run end to end and checked afterwards.

Five items are logged during cleaning: temperature, level, circulation flow, change in cleaning liquor concentration, and visual sample checks. Log every 30 minutes; when the concentration curve flattens and a withdrawn sample no longer effervesces, the end point is close. Elapsed time is not a substitute for an end point determination.

Corrosion monitoring runs alongside: coupons of the same material as the vessel are suspended inside under clause 5.2.11 of GB/T 25146-2010, and the corrosion rate is judged under Table 2 of that standard - not more than 5 g/(m2·h) on site for carbon steel and not more than 1.5 g/(m2·h) for stainless steel. If a coupon shows pitting, the liquor turns from clear to turbid, or the temperature rises abnormally, stop the pump and investigate rather than circulating on to save time.

6. Step 7: Waste Liquor Handling and Rinse Displacement

Waste liquor is collected separately by acidity and alkalinity, neutralised to pH 6-9, and then sent to the effluent treatment system or to a licensed contractor; it is never discharged to the storm drain. Transfer and disposal documents are retained as part of the acceptance file.

Rinse displacement runs in three moves: displace the cleaning liquor with clean water, neutralise residual acid or alkali, then rinse to neutral. On stainless steel equipment a chloride check is made before rinsing is signed off, and the rinse continues if the figure is over limit. This step is the real reason many vessels show rust shortly after cleaning, and it belongs in the procedure's step table.

7. Step 8: Passivation and Acceptance

Passivation is a routine step, not an option: once the acid clean and rinse have passed, passivate immediately so that the vessel wall, welds and coil surface form a passive film, then rinse to neutral and blow dry rather than leaving the vessel wet. Enamel reactors that are not acid passivated are still blown dry after a passed rinse, with the lining condition recorded.

Acceptance runs on two tracks. The visual track checks the wall, coil and agitator for residual hard scale, flash rust and corrosion marks at welds. The data track is judged under GB/T 25146-2010 and HG/T 2387, with scale removal not below 95% for carbonate scale, rust and oil deposits and not below 85% for sulphate scale, silicate scale and other deposit types (including slime), the before-and-after test results being the acceptance basis; the actual figure depends on deposit type, thickness, material, chemical system and site conditions.

Four deliverables close the job: the cleaning procedure (medium, temperature, pressure limit), the process record (temperature, concentration or pH, sample photographs), the acceptance report (coupon and re-test results), and the waste liquor disposal documents. The jacket and the interior are accepted separately rather than under one conclusion, which is the step most often missed on reactors with coils and jackets.

8. Frequently Asked Questions

Does a reactor have to be shut down for cleaning?

Yes for the interior. A reactor has no continuous process flow inside the vessel, so on-line circulation cannot form a working circuit. The practical compromise is a shorter shutdown window: the jacket can be cleaned on line, while the acid clean and passivation inside still require a shutdown, typically 2-4 days including pipework, cleaning, passivation and acceptance.

How do we clean an enamel reactor without spalling the lining?

Three hard limits: no fluoride system, because HF and fluorides attack the glass lining; no cold liquid into a hot vessel, because thermal shock is the main cause of spalling, so the heating rate is held below 20 C per hour; and no metal tools struck inside. Where the lining is already spalled, the water jet is kept off that area and replaced by low-pressure, high-flow rinsing.

Why does a stainless steel reactor rust after cleaning?

Usually chloride pitting or insufficient passivation. On 304 and 316L the passive film breaks down in chloride media, starting as spots and developing into pits. Control chloride in the cleaning liquor and rinse water, passivate immediately after the acid clean, then rinse to neutral and blow dry. If the rust has spread into patches with pitting, the vessel needs re-pickling and re-passivation rather than wiping.

How long does reactor cleaning take and what does it cost?

A typical 5-20 m3 reactor takes 2-4 days per unit, including pipework, cleaning, passivation and acceptance. Cost depends on deposit type and thickness, whether entry into the vessel is needed, and the volume of waste liquor. Pricing follows the deposit sample and site conditions; a scaling risk diagnosis report can be generated on line first, then sent to our engineer for a quotation by phone at +86 18952832843.

Can the waste liquor be discharged directly?

No. Acid and alkaline liquors are collected separately, neutralised to pH 6-9, and then sent to the effluent treatment system or a licensed contractor in line with local environmental requirements, with transfer and disposal documents kept. It is also why the expected waste liquor volume belongs in the cleaning procedure, since direct discharge is both non-compliant and incomplete as an acceptance record.

Related Reading

Process selection on reactors depends heavily on the equipment type and material:

• Reactor Cleaning Technology - enamel, stainless steel and carbon steel routes
• 304/316L Stainless Steel Tank and Reactor Passivation
• Industrial Steam Boiler Chemical Descaling Technology
• Thermal Oil Boiler and Pipeline Cleaning
• Equipment Scaling Diagnosis Tool · Maintenance Cycle Calculator

All cleaning processes, process control and acceptance criteria in this article follow GB/T 25146-2010 Quality acceptance specifications of chemical cleaning for industrial equipment and HG/T 2387 Quality standard for chemical cleaning of industrial equipment. Water jetting inside the vessel follows GB/T 26148-2025 Safety specification for high-pressure water jetting cleaning operations, with equipment complying with GB/T 26135-2020 High-pressure cleaning machines. Temperature and time parameters are fixed by the bench test and site conditions.

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