Due to the corrosion resistance and long service life of welded steel tube, seamless steel pipes are gradually replaced in more and more fields, but it is necessary to understand the performance of welded pipes to make them reasonably utilized in order to maximize its service life.

The exposed metal surface will undergo electrochemical or chemical reactions, and it will be evenly corroded. The parts with weak corrosion resistance in the purification film on the surface of the welded pipe will form a pitting reaction due to the self-excited reaction, forming small holes, and with the proximity of oxygen ions, a strong corrosive solution is formed and the rate of the corrosion reaction is accelerated. In addition, the occurrence of intergranular corrosion inside the welded pipe leads to cracking, which will pulverize the purification film on the surface of the welded pipe.

Therefore, the surface of the welded pipe should be regularly maintained to ensure its clean surface and prolong its service life. When washing the surface of the welded pipe, it is necessary to carefully avoid surface scratches; it is forbidden to use bleaching powder, washing liquid containing abrasives, grinding tools for steel balls, etc.; in order to remove excess washing liquid, rinse the surface with clean water after washing.

When there is dust on the surface of the welded pipe and it is easy to remove contaminants, it can be washed with weak ionic detergent, or with alcohol or organic solvent (ether, benzene).

There are grease or lubricating oil contaminants on the surface of the welded pipe. After cleaning with a soft cloth, wash with neutral detergent, ammonia solution or special detergent.When bleach and various acids are attached to the surface of the welded pipe, rinse it with water immediately, then dip it with ammonia solution or neutral carbonic acid and aqueous solution, or wash it with neutral detergent or warm water.

When there is a rainbow pattern on the surface of the welded pipe (caused by excessive use of detergent or oil), it can be washed with warm water neutral detergent when washing. When there is rust caused by pollutants on the surface of the welded pipe, it can be washed with 10% nitric acid or abrasive detergent, or it can be washed with special cleaning chemicals.

The second step is degreasing. The so-called degreasing is to remove the grease and dirt on the surface of the black pipe, so as not to affect the pickling effect. General alkaline washing can be achieved by burning or alkaline washing. The alkaline cleaning time of the welded pipe equipment should be kept at 8-10 minutes.

The last is pickling. Although alkaline washing can also remove stains, the two types of stains are slightly different. The purpose of pickling is to remove the iron oxide scale on the surface of the steel pipe. The advantage is that it can be operated at room temperature.It has a strong ability to remove iron oxide scale, the base metal is less corroded, and the absorbed hydrogen is less, and the possibility of contamination by carbon black residues is small.The iron salts produced by pickling are oxides, which have a large deep angle and are easy to remove, and have no effect on galvanizing. From the point of view of galvanizing, hydrochloric acid pickling is more suitable.