Chemical descaling protocol for the metalworking industry

This protocol describes how to remove limescale, rust, oil and grease from metal parts by prior degreasing, immersion in an acid bath, rinsing to neutral pH and temporary anti-corrosion protection. The doses, temperatures and compatibilities come from the technical data sheets of the products cited; where the data sheet does not set a value, the protocol says so and refers to visual inspection and pH.

Materials required

• Prior degreaser: Desgrasol MO (mixed with water at 1:4) for burnt oil; Grassol (neat or down to 1 %) for general grease; Deplac (neat or down to 10 %, at 70-80 °C) for burnt-on grease
• Acid descaler for the immersion bath: Nitracip Pro (1-5 %, 40-60 °C), Acid Pro (2-5 %, 40-70 °C), Detercal 1N (15-20 %) or Detercal (10-20 %, 40-60 °C)
• Boost for old scale deposits: Vacid (50-100 g/l)
• Acidic cleaner for stainless steel and aluminium: Clinox (neat or at 25 %)
• Temporary anti-corrosion protection: Anti Ox aerosol; stainless steel polishing: Linox
• Dielectric degreaser for electrical components: Electronic or Di elec
• Plenty of water for rinsing, pH meter or indicator paper, thermometer
• Full personal protective equipment (see safety section)

Step-by-step procedure

1. Inspecting and sorting the parts: Examine the parts to identify the type of deposit (limescale, rust, grease or oil) and, above all, the base material. Compatibility rules: an acid descaler such as Decal attacks iron, cast iron and zinc, whereas aluminium, copper and copper alloys are practically not vulnerable when cold. The alkaline degreasers Grassol and Deplac can be used on all types of metal with the exception of aluminium. Sort by material, set aside electrical components (they do not go in the bath) and record the batch.
2. Prior surface degreasing: For burnt oil from engines and machinery, mix Desgrasol MO with water at a 1:4 ratio, apply by spraying (the emulsion forms a foam that clings to vertical surfaces), let it act for about 5-10 minutes and rinse with pressurised water. For general grease on metals other than aluminium, Grassol is used neat or diluted down to 1 % and can be applied with a pressure washer. If there is burnt-on grease, Deplac is applied neat or diluted down to 10 % at about 70-80 °C, left to act for a few minutes and rinsed with plenty of water.
3. Preparing the descaling bath: Add the acid to the water, never the other way round, and choose the product according to the deposit: for limescale and rust, Nitracip Pro (nitric acid, descaler and deoxidiser) by immersion at 1 to 5 % at 40-60 °C; where there are chrome-plated or enamelled parts or rubber seals, Acid Pro by immersion at 2 to 5 % at 40-70 °C, since it does not attack them; in installations with rust and scale with adhered grease, Detercal 1N by immersion diluted at 15 to 20 %, which contains corrosion inhibitors for ferrous metals; for boilers, condensers and circuits, Detercal (orthophosphoric acid, non-foaming) at 10 to 20 % at 40-60 °C. The pH reference is the value at 1 % on the data sheet, for example 1.5 ± 0.5 for Nitracip Pro.
4. Immersion and temperature control: Place the parts in the basket and immerse them completely. Keep the temperature within the range on the data sheet of the chosen product (40-60 °C for Nitracip Pro and Detercal, 40-70 °C for Acid Pro). The data sheets do not set a fixed immersion time, because it depends on the thickness of the deposit; as an order of magnitude, Nitracip Pro works in recirculation for about 15-20 minutes and Vacid in manual use calls for contact times of at least 8 minutes. Agitate gently at intervals. On low-grade steels the use of Vacid at high concentrations must be avoided.
5. Intermediate check and boost on old scale: Remove a sample part, rinse it and assess the result. If residue persists, extend the immersion or brush carefully without damaging the base metal. For old scale deposits, the Vacid data sheet specifies increasing the dose to 50-100 g/l. When the bath loses effectiveness and its pH drifts away from the reference value on the data sheet, the acid is spent and must be renewed.
6. Rinsing to neutral pH: Remove the basket and rinse immediately with plenty of water, as required by the Detercal 1N data sheet. Continue rinsing until neutral pH (the criterion on the Detercal data sheet), checking with indicator paper or a meter on the water draining from the parts.
7. Alkaline neutralisation (optional): If the internal procedure requires chemical neutralisation in addition to rinsing, use a dilute alkaline solution and check that the drain water is at neutral pH. The catalogue does not include a specific neutraliser, so no dose is given; what matters is the rinsing to neutral pH in the previous step.
8. Finishing stainless steel and aluminium: Stainless steel and aluminium parts do not require the strong bath: they are treated with Clinox, an acidic degreasing cleaner that cleans and protects surfaces. It is used neat for stubborn soiling and at a dose of 25 % for maintenance cleaning; let it act for a few minutes and rinse with water. For finishing visible surfaces, Linox is sprayed sparingly and rubbed with a dry cloth, leaving a glossy film that protects against grease and splashes; do not use on food preparation surfaces.
9. Cleaning electrical components (outside the bath): Motors, alternators, transformers and electrical panels are cleaned with a dielectric degreaser, always with the system switched off. Electronic is fast-evaporating and requires no subsequent drying: spray from a distance of approximately 30 cm and use a dry brush if necessary; it does not attack metal surfaces or leave residue. Di elec evaporates slowly but completely: spray from the same distance, let it act and then dry with an air jet. Both may slightly attack certain plastics (Di elec, especially polystyrene).
10. Drying, anti-corrosion protection and final inspection: Drain and dry with clean compressed air or hot air until no droplets or salt marks remain. On ferrous parts to be stored, shake and spray Anti Ox generously: it leaves a thin, permanent, non-drying protective film, protects against moisture and corrosion and replaces protective chrome, wax, lacquer or paint coatings, with easy application and removal. Inspect, record and store in a dry place.

Verification and control

Check at each stage: (1) actual bath dose against the range on the data sheet (1-5 % for Nitracip Pro, 15-20 % for Detercal 1N by immersion); (2) temperature within the product's range, before immersion and every 15 minutes; (3) bath pH compared with the pH at 1 % on the data sheet, as an indicator of depletion; (4) neutral pH of the drain water; (5) visual inspection with no deposit residue or attack on the base metal; (6) absence of droplets and salt marks after drying; (7) record of batch, product, dose, temperature, time and result.

Safety and PPE

• Panoramic chemical safety goggles and face shield when handling concentrated acids
• Chemical-resistant gloves, protective clothing and PVC apron
• Sufficient ventilation in the bath area; otherwise, respiratory protective equipment
• Always add the acid to the water, never the water to the acid
• Do not mix with other chemicals (a warning common to all the data sheets); never acids with chlorinated products or with alkaline degreasers
• Dielectric degreasers are used with the electrical system switched off and away from ignition sources
• Emergency shower and eyewash station accessible; consult the safety data sheet of each product

Recommended Instaquim products

(1) Prior degreasing: Desgrasol MO (burnt oil), Grassol (cold alkaline) and Deplac (carbonised grease). (2) Acid bath: Nitracip Pro (nitric, deoxidising, non-foaming), Acid Pro (controlled foam, compatible with chrome plating and seals), Detercal 1N (corrosion inhibitors for ferrous metals), Detercal (orthophosphoric, non-foaming) and Vacid as a boost. (3) Stainless steel and aluminium: Clinox and Linox. (4) Protection: Anti Ox. (5) Electrical: Electronic and Di elec.

Applicable regulations: Regulation (EC) No 1272/2008 CLP (classification, labelling and packaging of mixtures), Regulation (EC) No 1907/2006 REACH (registration and safety data sheets) and Regulation (EC) No 648/2004 on detergents. If the parts come into contact with food, Regulation (EC) No 852/2004 also applies.

Frequently asked questions

Which acid descaler should I choose for parts with both limescale and rust?

Nitracip Pro, formulated with nitric acid, has high descaling and deoxidising power: by immersion it is used at 1 to 5 % at 40-60 °C. If there is also adhered grease, Detercal 1N combines degreasing power and corrosion inhibitors for ferrous metals and is applied by immersion at 15 to 20 %.

Can I put chrome-plated parts or parts with rubber seals in the acid bath?

Yes, with Acid Pro: its data sheet states that it does not attack chrome-plated or enamelled materials, rubber seals or plastic. By immersion it is dosed at 2 to 5 % at 40-70 °C. Detercal offers the same compatibility with chrome plating and enamel.

What about aluminium and stainless steel?

They should not be treated with the alkaline degreasers Grassol and Deplac, whose data sheets exclude aluminium. For both metals the indicated product is Clinox, an acidic degreasing cleaner that cleans and protects; it is used neat for stubborn soiling and at 25 % for maintenance.

How long should the parts remain immersed?

The data sheets do not set a fixed immersion time because it depends on the thickness of the deposit. As a guide, Nitracip Pro works in recirculation for about 15-20 minutes and Vacid in manual use requires at least 8 minutes of contact.

How do I know the rinsing is sufficient?

The Detercal data sheet sums it up: rinse with water until neutral pH. Measure the pH of the water draining from the parts; as long as it remains acidic, product is retained and will cause rust after drying.

How do I protect the parts after descaling?

With Anti Ox, an anti-rust agent in aerosol form that is shaken and sprayed generously over the surface. It leaves a thin, permanent, non-drying film, protects against moisture and corrosion, with easy application and removal.

Can I clean motors and electrical panels with the same protocol?

No: electrical components do not go in the bath. They are cleaned with a dielectric degreaser, with the system switched off and spraying from about 30 cm. Electronic evaporates quickly and requires no drying; Di elec evaporates slowly and is dried with an air jet.