Pipes or pipes without seams or welds are called seamless pipes. These pipes are solid metal tubes of uniform construction and strength, without joints. Ideally, each end of the tube is connected to the other without any joints. This increases the ability to withstand higher temperatures, pressures, mechanical stress, and corrosive atmospheres.

Seamless tubes or pipes are usually made from solid round rods of metals such as carbon steel, tungsten, stainless steel, or molybdenum. To transform it into a hollow tube, the metal piece is heated and rolled onto a mold.

Push and pull seamless tubing from a small piece of metal rod

Seamless pipes are shorter in length compared to welded pipes

Seamless pipe is more expensive than welded pipe

The seamless pipe provides a higher range of security measures

Seamless tubing offers high corrosion resistance

The seamless pipe has a homogeneous structure

Seamless pipes are widely used in oil refining, petrochemical, fertilizer, electric power, chemical industry, automobile, and other fields. These tubes are considered more reliable and stronger as they do not have any joints or welds. Seamless carbon steel pipes are also made as single or double non-systematic or fixed-length linear units.

The ability to withstand pressure allows these pipes to be used in a variety of processes. Seamless pipes are used for high-pressure equipment, heat exchanger pipes, steam discharge pipes, low-temperature pressure vessels, air cooler pipes, air preheaters, and steam trap pipes.

The production methods of seamless pipes are roughly divided into the cross-rolling method (Mennesmann method) and the extrusion method. The former method is to perforate the pipe with inclined rolls, and then stretch it with a rolling mill. This method has a fast production speed, but has high requirements on the machinability of the tube blank, and is mainly suitable for the production of carbon steel and low alloy steel pipes. The latter method is to perforate the tube billet or steel ingot with a piercer, and then extrude it into a steel pipe with an extrusion machine. The efficiency of this method is lower than that of the skew rolling method, and it is suitable for the production of high-strength alloy steel pipes. Both the cross-rolling method and the extrusion method must first heat the tube billet or steel ingot, and the produced steel tube is called a hot rolled tube.

There are two methods of cold working: one is the cold drawing method, which is to draw the steel pipe through a drawing die to make the steel pipe gradually thinner and elongated; the other method is the cold rolling method, invented by the Mennesmann brothers. The application method of the hot rolling mill in cold working. Cold working of seamless steel pipe can improve the dimensional accuracy and processing finish of the steel pipe, and improve the mechanical properties of the seamless pipe material.

Hot rolling is hot working

Cold drawing is a cold working

The main difference is: hot rolling is rolling above the recrystallization temperature, and cold rolling is rolling below the recrystallization temperature.

Cold rolling is sometimes heated, but the temperature is relatively low because work hardening occurs after cold rolling. If the forming requirements of the material are relatively high, annealing is required.

Cold rolling and hot rolling are generally plates or profiles, while cold drawing is generally cylindrical cross-section wire. In addition, hot-rolled sheets are generally steels with high alloy content and high strength, while cold-rolled sheets are low-carbon and low-alloy steels. Cold rolling can improve the strength and ensure the surface quality of the material.

The difference between cold-drawn seamless steel pipe and hot-rolled seamless steel pipe is that the plates are different. Due to their different manufacturing processes, seamless steel pipes are divided into hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes. Cold-drawn (rolled) tubes are divided into round tubes and special-shaped tubes:

Cold-drawn steel pipe generally requires multiple drawings, and corresponding stress relief annealing should be carried out between each drawing to ensure the smooth progress of the next cold drawing.

From the outside, the cold-rolled seamless steel pipe tends to have a smaller diameter, while the hot-rolled seamless steel pipe tends to have a larger diameter. The precision of cold-rolled seamless steel pipe is higher than that of hot-rolled seamless steel pipe, and the price is also higher than that of hot-rolled seamless steel pipe. Cold-drawn seamless pipes generally have a small diameter, mostly below 127mm, especially since the outer diameter precision of cold-drawn seamless pipes is very high, and the length of cold-drawn seamless pipes is generally shorter than that of hot-rolled seamless pipes. In terms of wall thickness, cold-drawn seamless pipes are more uniform than hot-rolled seamless pipes.

Performance hot rolling and cold drawing are the difference in the production process

Hot rolling is processing at high temperatures without changing the structural properties of the metal. Cold drawing is to perforate the round steel at a high temperature, and then cold draw it on a pipe drawing machine. Working in untempered conditions affects the crystal structure of the metal. In general, hot rolling has better mechanical properties than cold rolling. After heat treatment, its tensile strength, yield strength, plasticity, and toughness will all be improved. In addition, heat treatment can eliminate residual stress, while cold rolling may produce residual stress due to uneven deformation of steel during processing, which has a great influence on stability.

The above briefly introduces the industrial use and production process of seamless steel pipes and other related issues. If you want to know more or want to buy seamless steel pipes, please contact us.

BAOLAI is a professional custom seamless steel tube manufacturer. Seamless steel tubes are seamless hollow section round tubes. Seamless steel pipes are made of carbon steel, alloy steel, stainless steel ingots, or solid tube blanks, which are hot-rolled, cold-rolled or cold-drawn. Our seamless steel tubes are available in sizes 1/2"-36" to API, ASTM, BS, DIN and JIS standards for the transportation and construction of liquids and gases.