How are Seamless Boiler Tubes Made?

Boiler seamless tube is a kind of boiler tube and belongs to the category of seamless steel tube. The manufacturing method is the same as that of the seamless tube, but there are strict requirements on the steel type used in the manufacture of the steel tube. Boiler seamless tubes are often under high temperature and high pressure conditions when used, and the tubes will be oxidized and corroded under the action of high temperature flue gas and water vapor. Steel pipes are required to have high durable strength, high resistance to oxidation and corrosion, and good structural stability. Seamless tubes for boilers are mainly used to manufacture superheater tubes, reheater tubes, gas guide tubes, and main steam tubes for high-pressure and ultra-high pressure boilers.

How are Seamless boiler tubes made?

According to the use temperature, it is divided into two types: general boiler tube and high pressure boiler tube.

(1) Manufacturing method:
1. Both medium-pressure and high-pressure boiler tubes undergo the same initial process of manufacturing, which includes fine drawing, surface bright, hot rolling, cold drawn and heat expansion. However, the following steps are undertaken to make high-pressure pipes stronger and more resistant.
2. Heat treatment includes heating and cooling of the high-pressure boiler pipes which increases toughness, hardness and wear resistance. The different steps that come under heat treatment include quenching, tempering and annealing.
3. Quenching is done to increase the hardness of the high-pressure boiler tube. The pipe is heated evenly to an appropriate temperature and then quickly immersed into water or oil for instant cooling. This is followed by cooling in air or in the freezing zone.
4. Tempering is used to remove brittleness from the pipe. Quenching can cause the pipe to become tapped or broken.
5. Annealing can remove the internal stress in the pipe. In this process, the seamless tube is heated to the critical temperature and then left for slow cooling in ash or lime.

Seamless steel tube production process:

a. Hot rolled (extruded) seamless steel tube: round tube billet → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → tube removal → sizing (or reducing) → cooling → straightening →Hydrostatic test (or flaw detection) → marking → storage
b. Cold drawn (rolled) seamless steel tube: round tube blank→heating→perforation→heading→annealing→pickling→oiling (copper plating)→multi-pass cold drawing (cold rolling)→blank tube→heat treatment→Straightening→hydrostatic test (flaw detection)→marking→warehousing

(2) Boiler tube use:

① General boiler seamless tubes are mainly used to manufacture water wall pipes, boiling water pipes, superheated steam pipes, superheated steam pipes for locomotive boilers, large and small smoke pipes and arch brick pipes, etc.

② Seamless tubes for high-pressure boilers are mainly used to manufacture superheater tubes, reheater tubes, air guide tubes, and main steam tubes for high-pressure and ultra-high pressure boilers.

(3) Rust removal of the boiler tube:
There are several methods for removing rust from the boiler tube, the simplest being cleaning using a solvent and emulsion. However, this can remove only dust, oil, etc. but will not rid the pipe completely off organic remnants.
The second method is rust removal using manual or power tools. Tool cleaning can get rid of oxide coatings, welding slag and rust.
The most common method is through chemical and electrolytic methods, also known as acid cleaning.
Spray rust removal is the most ideal method for cleaning of the boiler tube as it can remove dirt, oxide and rust to a greater level. Furthermore, it can increase the roughness of the pipe.

How to choose good quality boiler tubes?

While choosing seamless boiler tubes, look for the following to pick out the right and good quality tubes:

1. Look at the cross-section of the tube. 

A good quality seamless tube will have a smooth cross-section and will be devoid of bumps and irregularities.

2. Check the surface of the boiler tube. 

A good quality boiler tube will have a smooth surface. If you find the surface to be rough and uneven, you can be sure that the quality is not up to the mark.

3. Check the density of the pipe to understand the percentage of impurities in the pipe. If the pipe shows low density, steer clear!

4. Make sure you check the trademark. 

Reputed manufacturers always put their trademark on their seamless tubes.

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