Additives in the chemical-polishing solution for PU insulated steel pipe inhibit corrosion and increase brightness. They can form a complex adsorption layer on the pipe surface, activating micro-protrusions and passivating micro-depressions so that polishing proceeds effectively. Such additives include viscosity modifiers, corrosion inhibitors, etchants, activators, and defoamers for the polishing bath; because of them, chemical polishing proceeds smoothly and a polished surface is obtained. Additive types include inorganic salts, organic salts, organic compounds, surfactants, and the like.
Inorganic salts: mainly sulfates, phosphates, nitrates, acetates, molybdates, chlorides, fluorides, etc.
Organic compounds: mainly glycerol (glycerin), Rodine, organic amines, gelatin, dextrin, sodium dodecyl sulfate, thiourea, polyols, cellulose ethers, polyethylene glycol, chloroalkylpyridines, halogen compounds, sulfosalicylic acid, azo dyes, etc. Brighteners with a strong gloss-enhancing effect include benzoic acid, salicylic acid, sulfonic acids, benzenediol, and fluorine-containing quaternary ammonium salts.
The type and concentration of chemical polishing additives for PU insulated steel pipe play a decisive role in polishing quality. The typical dosage is 0.1%–1.0%, depending on the composition and temperature of the polishing solution. Thiourea readily decomposes and deteriorates at high temperatures, so it should not be used at high temperatures. Some additives, such as bone glue, dyes, salicylic acid, and hydroquinone, should be prepared as saturated solutions in advance and then added to the polishing solution.
Corrosion inhibitors include rhodine (di-o-tolylthiourea) and hexamine (hexamethylenetetramine), typically used at 1–5 g/L. Brighteners include alkylpyridinium compounds, halogen compounds, and sulfosalicylic acid, used at 3–5 g/L.
