Chemical Cleaning of Blast Furnace Cooling Stave Pipes: Process and Blast-Furnace Plant Practice

Abstract: Scale inside the water pipes of blast-furnace cooling staves is a leading cause of lost cooling strength, furnace-shell overheating and even burned-out staves, and chemical cleaning is the dependable way to restore cooling capacity during a maintenance outage. This article explains how stave-pipe deposits form and how they are diagnosed, then presents the circulation cleaning loop — water flush, alkaline wash, acid clean, rinse and passivation — with different chemical systems for cast-iron and copper staves. A representative case and the acceptance criteria of GB/T 25146-2010 are included for ironmaking maintenance and equipment managers.

1. Structure of Blast Furnace Cooling Staves and the Danger of Scale

A blast furnace cooling stave is a cast-iron or copper cooling element with water pipes cast in or drilled through it, installed in rings against the furnace shell over the bosh, belly and stack. Cooling water flowing through the pipes carries away heat conducted through the lining and shell, keeping shell temperature in a safe range. The stave pipe is the most heat-loaded passage in this cooling chain, and its internal condition decides how well the whole furnace is protected.

Calcium carbonate scale typically conducts heat at only about 0.1–0.2 W/(m·K) (industry rule of thumb) — a small fraction of the thermal conductivity of cast iron. Once scale forms inside a pipe, heat is no longer carried away promptly, the stave runs hotter, flow resistance rises and the water rate drops, feeding a vicious cycle of "scale — overheat — lower flow — faster scaling." When a stave burns out, that zone loses its cooling protection: the shell glows, deforms or cracks, and the furnace must be blown down. Losses are counted in hours of production, which is why stave-pipe fouling is always high on the ironmaking plant's equipment-management agenda.

2. How Stave-Pipe Deposits Form, and Diagnosis Before Cleaning

Blast furnace cooling water is normally recirculated industrial water containing calcium and magnesium bicarbonates. On the heated pipe wall at roughly 40–60°C, bicarbonate decomposes and calcium carbonate crystallizes out; suspended solids, iron corrosion products and microbiological slime settle with it. The result is a composite deposit dominated by carbonate scale with rust and sludge, growing inward from the wall — the smaller the pipe bore, the sooner flow starts to decay.

Whether cleaning is due is judged from several diagnostics together. First, infrared shell thermography: a local hot zone usually marks a failing stave or blocked pipe. Second, water flow rate, the ratio of actual to design flow: a persistently low figure points to rising internal resistance. Third, scale-sample analysis, which identifies deposit type and quantity by acid dissolution and appearance. Fourth, material confirmation and corrosion-coupon inhibitor tests, which must be completed before any acid is used because cast-iron and copper staves need different chemical systems. Final judgement rests on the plant's monitoring data and equipment condition; Blue Star Cleaning can carry out the inspection and assessment on assignment.

3. Chemical Cleaning Process

Stave-pipe cleaning is done inside the scheduled blow-down window. The basic idea is to group the stave pipes of one furnace section into circulation loops: several pipes are connected in parallel through temporary pipework to an acid-resistant pump and a make-up tank, and the cleaning liquor circulates through each loop until the deposit has fully reacted. The number of groups follows the outage duration and tank capacity, and several loops can be cleaned in parallel without interfering with one another.

The standard sequence is: water flush and leak check → alkaline wash (oil and sludge removal) → water rinse → acid clean → rinse → passivation and pre-filming → inspection and acceptance. The alkaline stage uses LX-902 compound cleaner (alkali-stripping type) to strip oil, sludge and loosen the deposit. The main acid stage uses LX-903 compound cleaner, a chlorine-free sulfamic-acid-based formulation, which dissolves carbonate scale quickly with a low corrosion rate on cast iron and is always used with a dedicated inhibitor. Copper-stave circuits are cleaned separately with a citric-acid-based compound cleaner plus a BTA inhibitor at a temperature kept below 60°C to avoid excessive attack on copper. Cleaning temperature, circulation time and chemical dosage follow the scale analysis and coupon tests and are not set out here as a recipe.

Process control during the acid stage: the acid concentration and iron content are titrated at 30–60 minute intervals; the acid end point is reached when two consecutive acid readings differ by less than 0.2% and the Fe³⁺ content levels off. Corrosion coupons are hung throughout, and the corrosion rate is held to the limits of GB/T 25146-2010 Quality acceptance specifications of chemical cleaning for industrial equipment — carbon steel not above 2 g/(m²·h) and copper and copper alloys not above 1 g/(m²·h), with the coupon inhibitor test as the final reference.

After acid cleaning the metal surface is active and must be rinsed and passivated without delay. A low-concentration passivation solution is circulated to form a continuous, dense protective film on the pipe wall so the pipe does not rust back or corrode faster in the first weeks of service. Passivation liquor is collected separately and must never be mixed with acid waste for disposal.

4. Safety, Environment and Outage Organization

Blast furnace outage work is crowded with parallel trades, so chemical cleaning follows the plant's permit-to-work rules. Stave-pipe work involves elevated platforms and confined areas: pipe dismantling requires a signed work permit with isolation tags after the cooling-water system is confirmed drained and depressurized. The make-up and acid zones are fenced off, fume is controlled by covered tanks and ventilation, operators wear acid-proof suits, goggles and respirators, and wash-down water and first-aid supplies are stationed at the worksite.

Waste liquor is collected and handled in line with environmental requirements: acid waste and rinses are neutralized to pH 6–9 before discharge under the plant's rules or handover to a licensed disposal contractor; nitrite-bearing passivation liquor is collected separately to avoid ammonia-nitrogen exceedance. A waste-liquor disposal plan is prepared before work starts and agreed with the plant's environmental department so every stream is traceable.

5. Case Study: Descaling Cooling Stave Pipes at an Ironmaking Plant

In June 2026 Blue Star Cleaning took on the cooling-stave-pipe cleaning scope of a mid-campaign repair for a blast furnace at an ironmaking plant in East China. Infrared inspection before the outage had shown clearly elevated shell temperatures over the lower stack; sampled pipes carried 2–4 mm of predominantly hard carbonate scale with rust, and some loops were running below 80% of design flow.

Working inside an outage window of about 20 days, the team split the affected pipes into eight circulation loops and acid-cleaned them with LX-903 compound cleaner, preparing the cast-iron and copper circuits separately with independent temperature control, while corrosion coupons were monitored throughout. After cleaning, the pipes were rinsed, passivated and proof-flowed loop by loop: the scale removal rate exceeded 95% (carbonate scale, in line with GB/T 25146-2010, with pre- and post-cleaning testing as final acceptance evidence), the water flow rate recovered to around 96%, and shell temperature in the treated zones fell clearly after relight. No stave leaked and the work passed acceptance at the first attempt; the furnace has run steadily since.

6. Frequently Asked Questions

Q1: Why do blast furnace cooling stave pipes scale up and block? How often should they be cleaned?

Calcium and magnesium bicarbonates in the cooling water crystallize on the heated pipe wall and deposit together with suspended solids and iron corrosion products. Stave water runs hot under a high heat load, so it scales faster than ordinary exchangers. The cleaning interval depends on make-up water quality, water-treatment performance and operating temperature, and is usually planned together with the furnace mid-campaign repair; monitoring of flow rate and shell temperature is the practical guide. Blue Star Cleaning offers annual inspection and assessment.

Q2: Will chemical cleaning damage the cooling stave pipes?

No. Pipe material is confirmed and corrosion-coupon inhibitor tests are run before acid, a dedicated inhibitor is dosed during the acid stage, and the corrosion rate is monitored throughout against GB/T 25146-2010 (carbon steel not above 2 g/(m²·h)); cast-iron and copper staves each get a matched chemical system, with the copper circuits kept separately at controlled temperature. Blue Star Cleaning has never damaged a cooling stave pipe in 25+ years of such work.

Q3: Must cleaning wait for a furnace outage? Will it delay production?

The stave pipes are integral with the furnace and can only be worked on during a scheduled blow-down window. Blue Star Cleaning plans backwards from the outage schedule: the staves are grouped into circulation loops and several loops run in parallel, with a single group normally finished in 1–2 days depending on site conditions and the outage window. Call 18952832843 in advance to fit your repair schedule.

Q4: How much flow rate can be recovered, and how long does the effect last?

For predominantly carbonate scale, the removal rate reaches above 95% and the water flow rate usually recovers to around 95%, with pre- and post-cleaning measurement as the final acceptance evidence. How long the effect lasts depends on make-up water quality and operating practice; under normal conditions the staves run steadily until the next repair campaign, and Blue Star Cleaning provides follow-up visits within the warranty period.

Q5: How is blast furnace stave cleaning priced and what preparation is needed?

Pricing follows the number of circulation loops, pipe size and length, and the scale type and thickness; cast-iron and copper stave circuits are priced separately because their chemical systems differ. The plant should provide stave layout drawings and water-quality data in advance. Blue Star Cleaning surveys on site and analyzes scale samples free of charge before issuing the plan and quotation; invoicing follows acceptance. Tel: 18952832843.

All cleaning processes and acceptance criteria in this article follow GB/T 25146-2010 Quality acceptance specifications of chemical cleaning for industrial equipment.

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