After the seamless steel pipe is manufactured, it undergoes an acid pickling process, followed by galvanizing treatment according to customer requirements. There are generally three types of galvanizing methods: hanging galvanizing, air-blowing galvanizing, and galvanized strip. Hanging galvanizing for seamless steel pipes achieves the highest zinc coating weight, exceeding 500g per square meter. Air-blowing galvanizing achieves around 300g per square meter, while galvanized strip welded pipes, the most commonly used but with the least amount of zinc coating, have a zinc coating weight of only 60-150g per square meter. Only after the seamless steel pipe has been galvanized can the thread cutting process begin. This process is carried out on specialized lathes, with strict requirements for taper, pitch, and thread type. Standards vary, including American, British, and National Standards. Both ends of the seamless steel pipe undergo thread cutting, thread cleaning, and inspection before one end is fitted with a pipe coupling and the other with a plastic cap to protect the threads. Galvanized steel pipes with threaded ends are further categorized into American Standard and British Standard, with thread counts of 8 or 10 teeth per inch.
The manufacturing of pipe couplings is the most intricate and crucial part of the entire product, as they are the components that bear the most pressure in the entire system. The material quality of pipe couplings must be equal to or higher than that of the seamless steel pipe itself. After being cut from round steel, the pipe couplings are machined to precise dimensions on lathes, followed by thread cutting. Finally, the threads and dimensions are inspected for quality assurance.
Substandard hot-dip galvanized spiral steel pipes often exhibit a folding phenomenon on their surface. This folding is caused by the formation of folds during the manufacturing process, which appear as longitudinal striations on the pipe. This phenomenon arises when manufacturers prioritize efficiency over quality, resulting in excessive pressure during the rolling process that leads to folding. Such substandard pipes are prone to cracking during use, significantly reducing the overall strength of the steel.
