Welded steel tubes are widely used in water supply engineering, petrochemical industry, chemical industry, electric power industry, agricultural irrigation, urban construction, etc. Due to its cheap price, seamless pipes are gradually replaced in many fields. Compared with the welded pipe, the maximum diameter of the seamless pipe sizes can reach 650mm, and the minimum diameter is 0.3mm.
1. Clean the surface of the welded pipe: keep the surface clean, remove rust, iron oxide, etc., so as to ensure the adhesion of the coating! Therefore, the galvanized welded pipe must be surface pretreated. The usual pretreatment includes degreasing, water washing, pickling, re-washing, etc. Dry galvanizing also includes storage, solvent application, drying, etc.
2. Degreasing, the so-called degreasing is actually to remove the grease and dirt on the surface of the clarinet, so as to avoid affecting the pickling effect. Equipment degreasing can also be achieved by burning or caustic cleaning, which is usually chosen. The alkaline washing solution contains about 10-12% sodium hydroxide aqueous solution, and the temperature is 70-80°C. The time for alkaline cleaning of welded pipe equipment is usually 8-10 minutes. Take your time, depending on the situation.
3. In addition to alkali washing, pickling can also be used. Both are used to remove stains, but the stains are slightly different. Pickling is to remove the oxidized iron scale on the surface of the steel pipe.
4. In addition to pickling with hydrochloric acid. Its advantages are that it can be operated at room temperature, has a strong ability to remove iron oxide scale, has less corrosion on the base metal, absorbs less hydrogen, and is not easy to produce carbon black residue pollution. The iron salt formed by pickling is an oxide with a large depth angle, which is easy to remove and will not affect galvanizing. From the perspective of galvanizing, hydrochloric acid pickling is very suitable.