As far as welding technology is concerned, the welding method of spiral steel pipe is the same as that of cold-drawn steel pipe. The production process of cold-drawn steel pipe is relatively simple. The main production processes are high frequency welding cold-drawn steel pipe and submerged arc welding cold-drawn steel pipe. The straight seam pipe has high production efficiency, low cost and rapid development. But cold-drawn steel pipe will inevitably have a lot of T-welds, so the probability of welding defects is greatly increased, and the welding residual stress at T-welds is larger, weld metal is often in a three-dimensional stress state, which increases the possibility of cracking. Spiral steel pipe and cold-drawn steel pipe are one kind of welded steel pipe. They are widely used in national production and construction. Spiral steel pipe and cold-drawn steel pipe have many differences because of different production processes. The differences between spiral steel pipe and cold-drawn steel pipe are discussed in detail below. 在业内生产较大口径冷拔钢管时会使用丁字焊技术，即将一段段短的冷拔钢管再进行对接，接成符合工程需要的长度，丁字焊冷拔钢管缺陷的机率也大大提高，而且丁字焊缝处的焊接残余应力较大，焊缝金属往往处于三向应力状态，增加了产生裂纹的可能性。
In the production of large diameter cold-drawn steel pipes in the industry, T-weld technology will be used, i.e. a short section of cold-drawn steel pipes will be joined to meet the needs of the project, and the probability of defects in T-welded cold-drawn steel pipes will be greatly increased. Moreover, the welding residual stress at T-weld seam is large, and the weld metal is often in a three-dimensional stress state, which increases the possibility of cracking.
The strength of spiral steel pipe is generally higher than that of cold drawn steel pipe. The main production process is submerged arc welding. The spiral steel pipe can produce welded pipes with different diameters with the same width blank, and can also produce welded pipes with larger diameters with narrower blank. However, compared with the straight seam pipe of the same length, the length of the weld increases by 30-100%, and the production speed is lower. Therefore, most of the smaller diameter welded pipes are welded by straight seam welding, while the larger diameter welded pipes are mostly welded by spiral welding.
Moreover, according to the technological requirements of submerged arc welding, each weld should have arc initiation and arc extinguishing points, but each cold-drawn steel pipe can not achieve this condition when welding annular seam, so there may be more welding defects at arc extinguishing points. When a pipe is subjected to internal pressure, there are usually two main stresses on the pipe wall, i.e. radial stress and axial stress.
Someone always asks, what is the difference between spiral steel pipe and cold drawn steel pipe? Which would be better? Generally, DN350 or above, why do spiral steel pipes need to be used instead of cold drawn steel pipes? These doubtful questions, and so on, have now summarized some of this knowledge, hoping to have some help for purchasers and distributors. Perhaps the summary is not comprehensive enough, but also hope that the general public put forward better suggestions.
Specifically speaking, spiral steel pipe and cold-drawn steel pipe belong to a weld form of welded pipe. They are generally used in different areas.
There are general DN350 or more, why use spiral steel pipe instead of cold-drawn steel pipe for larger diameter? The reasons are explained now.
Because the weld seam of spiral steel pipe is spiral, the pressure of liquid will be distributed on each side of the pipe to enhance the strength of the pipe.
If the cold-drawn steel pipe is used, the general large pipe is rolled up and welded directly with steel plate. The larger steel plate is needed, which greatly increases the difficulty of production, so the larger diameter of the pipe will use spiral pipe.
As for which is better, because the scope of application of the two is different, there is no way to say which is better, it should be said that each has its advantages.
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