Galvanized steel pipe is divided into cold galvanized pipe, hot galvanized pipe. Cold galvanized pipe has been banned, hot galvanized pipe is also the country to promote temporary use. Galvanized steel pipe surface with hot dip plating or galvanizing layer of welded steel pipe. Galvanized steel pipe can increase corrosion resistance and prolong service life. Sixties and seventies, the international developed countries began to develop new pipe, and have banned galvanized pipe. China’s Ministry of Construction and other four ministries also issued a clear document from 2000 onwards banned galvanized pipe as a water supply pipe, the current new district cold water pipe has rarely used galvanized pipe, some district hot water pipe is galvanized pipe.
Often said galvanized pipe is now mainly used for gas transmission, heating. Galvanized pipe as a water pipe, use a few years later, a large number of rust inside the pipe, the yellow water flowing out not only pollute sanitary ware, but also mixed with the non-smooth inner wall of bacteria; The high content of heavy metals in water caused by rust is harmful to human health.
As the name implies, cold galvanized pipe is through the method of galvanizing, the outer wall of the steel pipe is coated with a layer of zinc. This treatment method is completely different from the principle of hot galvanization, so we call it cold galvanizing pipe. It is precisely because this method does not change the chemical composition of the steel pipe surface so the stability of the zinc coating is not high.
Difference between galvanized pipe and hot-dip galvanized pipe:
1, the process is different, a chemical treatment, a physical treatment; Hot-dip galvanizing coating is firm and not easy to fall off
2, hot galvanizing coating thick, so strong corrosion resistance. And galvanized (electroplating) coating uniform, surface quality is better, the coating thickness is generally between a few microns to ten microns.
3, hot-dip galvanizing is a chemical treatment, belongs to the electrochemical reaction. Galvanization is a physical treatment, just brush a layer of zinc on the surface, there is no galvanization, so the zinc layer is easy to fall off. Hot-dip galvanizing is used in construction.
4, hot-dip galvanized pipe is to make molten metal and iron matrix reaction to produce alloy layer, so that the substrate and the coating combined.
What should be noticed in the welding of galvanized pipe?
- Galvanized steel pipe with diameter greater than 100mm should be connected by flange or special pipe fittings.
2, galvanized steel pipe and flange welding, in order to ensure the welding quality, should be the welding mouth galvanized treatment, the application of hand grinding wheel or sand paper to clean the galvanized layer, or gas welding flame to clear the zinc layer.
3, galvanized steel pipe and flange welding should be galvanized twice.
Measures to ensure welding quality include:
1, the human factor is the focus of gas galvanized pipe welding control. Due to lack of necessary post-weld control hand
Section, easy to jerry-building, affecting quality; At the same time, the welding particularity of galvanized pipe makes it difficult to ensure the welding quality. Therefore, skilled welders who hold the appropriate boiler pressure vessel or equivalent welder’s certificate should be selected prior to the commencement of work. Carry out the necessary technical training and disclosure, refer to the boiler pressure vessel welder examination rules for on-site examination and approval, give the permission to enter the site welding. And shall not be replaced at will, to ensure the welding of the pipeline welders relatively stable.
2, welding material control: to ensure that the procurement of welding materials is the normal channel, there is a warranty, certificate, meet the process requirements; Welding material acceptance, lead material formalities to formal and complete, electrode head recovery control strict, to ensure the flow direction, dosage; Welding materials should be strictly baked according to the process, and not more than half a day of supply.
3, welding machine; Welding machine is welding machine, must ensure reliable performance, meet the process needs; Welding machine must have qualified current, voltage meter, to ensure the correct implementation of welding technology. Welding cable can not be too long, long to adjust the welding parameters.
4, welding process method: ensure the strict implementation of special operation methods of galvanized pipe, according to the welding process before welding groove inspection, welding technology parameters, operation method control, after welding appearance quality inspection, when necessary, add after welding non-destructive testing. Control welding level, welding material consumption of each crossing.
5, welding environment control: to ensure the welding temperature, humidity, wind speed in line with the process requirements. Welding shall not be performed unconditionally.