The steel temperature in pipe production is the main distinction between hot-rolled and cold-rolled seamless pipes.
While both these products go through similar shaping processes, the steel used in the former production type is above the recrystallization temperature, usually well above 900 Degrees Celsius.
In contrast, when making cold-rolled pipes, steel ingots and billets get passed through the mills at a much lower heat, typical at room temperature.
This difference in temperature affects many factors of both pipe types, including finish, torsional resistance, residual stress, and more.
Cold roll pipes must first pass through the hot rolling process. As an extension of the process, producing cold-rolled pipes involves more fuel, labor, and operations than hot rolling.
Steel ingots and billets are necessary to make seamless pipes. Unlike ERW or LSAW pipes, these products are not electrically welded and fused but rather shaped out of steel blocks. To make this possible, heating is necessary.
Therefore, before steel pipes can be cold-rolled, they must pass through the hot rolling process. This step is mandatory because the steel blocks get perforated into hollow tubes during this process.
The steel must exceed the recrystallization temperature to facilitate the smoothness of the production. Only when the alloy reaches this temperature can it be properly shaped.
Before cold rolling, the steel pipes made via hot rolling must pass through the pickling step. The exposure to extreme temperatures during production results in the formation of scales on the tube surface.
This covering is mainly composed of different oxides and can get washed away using oil or water. This process of scale-removal is pickling.
Annealing/Profile Rolling/Cold Rolling
The pipes are ready for cold rolling when the scales have been successfully cleaned. The rolling method employed is profile rolling, and here the steel pipe passes through multiple rolls at room temperature.
- Manufacturers resort to cold rolling to increase the mechanical uses of steel pipes.
- Cold rolling gives the steel greater hardness as the grain gets reoriented from the substance micros hardening with the crystal structure change.
- Cold-rolled tubes have more applications than hot-rolled ones because they have a higher yield strength.
During cold rolling, the tube goes through several shaping operations to get the size/shape right. Many manufacturers use reversing mills to reverse the tube back into the roller in case of any defects. The product goes through the mills multiple times to get the proportions and thickness correctly.
Cold requires cannot achieve the same thickness-reducing effects as hot rolling in one go. For this reason, multi-strand mills and thicker gauges get used. The production also costs more than hot rolling, which is reflected in the product price.
Industry Specifications for Seamless Pipes
Since ASTM A513 covers the specifications for mechanical tubing made from cold-rolled steel, it forms the basis of many production processes.
|ASTM A513 Properties||Details|
|Range of Pipes||These standards cover carbon steel grades 1008 and above, including grades 1021, 1026, 1524, 4130, and 4140.|
|Testing requirements||Tensile, elongation, and yield testing aren't required under A513 specifications unless specifically requested.|
|Uses||These requirements are well suited for electrical welded and alloy steel tubings and get mostly used by the automobile and mechanical industry.|
General Features Of Cold Rolled Pipes
- Cold rolling is used to produce round or specially shaped pipes. Cold-rolled pipes have a lower diameter than hot-rolled pipes, with a maximum outer diameter of 6 mm.
- Pipes made via this rolling method have thin walls up to 0.25 mm thick.
- Temperatures for cold rolling should be well under 1652 Degrees Fahrenheit and typically limited to room temperature.
- Cold-rolled pipes possess greater dimensional accuracy than hot-rolled ones.
- Since they go through extensive shaping operations, cold-rolled pipes are harder and have a smoother surface area.
|Maximum Percentage||0.6 %||0.04 %||99.53 %||0.23 %||0.05 %|
Important Physical Properties
- Yield Strength
- 511.59 mpa
- Max. Tensile Strength
- 910.10 mpa
- Max. Elongation
- 22 %
- Below 1652 Degrees Fahrenheit
- 0.28 Lb/in3
Advantages Of Cold Rolled Pipes
Consistent thickness, smooth aesthetic finish- home appliances, metal furniture, construction materials. The reason manufacturers choose to cold roll their pipes is because it increases the marketability of the product.
Among other advantages, not only is cold-rolled pipes stronger than hot-rolled pipes, but they are also more bendable. Their other characteristics include.
- Cold rolling increases the strength of the pipe, with a 20% increase in hardness.
- Cold-rolled pipes have a higher tolerance despite being smaller and thinner than hot-rolled pipes.
- To produce cold-rolled pipes, steel billets get passed through several rollers. This equipment squeezes and compresses the metal, helping increase the durability and yield strength of the product.
- In cold rolling, pipes are processed further after the exposure to the heat, helping them maintain a consistent uniformity.
- Cold-rolled tubes contain lesser amounts of carbon than hot-rolled ones. This quality makes it smoother, more consistent, and easier to process for blacksmiths.\
- Cold rolled steel tubing has an improved surface finish, boosting its aesthetic appeal.
- Cold rolling improves dimensional accuracy, leading to better product precision and concentricity.
- Cold-rolled pipes have more mechanical properties than hot-rolled ones, increasing their value.
Application Of Cold Rolled Pipes
Cold rolled pipes have a high aesthetic finish, with a smooth surface finish and well-proportioned dimensions. In addition, they are harder while being easier to shape than hot-rolled pipes. For these reasons, cold-rolled pipes have applications in things like;
- Cold-pressed pipes can be used in metal furniture, including desks, filing cabinets, tables, chairs,
- They even get used motorcycle and car exhaust pipes in the automobile industry.
- Cold-pressed pipes can be used to make computer cabinets and home appliances as shelving, lighting fixtures, and more.
- The high aesthetic value of cold-rolled pipes makes them a valuable construction material for projects focusing on visual appeal.
Disadvantages Of Cold Rolled Pipes
- Cold-rolled steel billets contain lesser amounts of carbon than hot-rolled ones. While this makes the product smoother and easier in quality, it also adds to the cost, making them more expensive than hot-rolled pipes.
- These pipes are smaller than hot-rolled ones, limiting their application in oil and gas transport industries.
- Cold rolled pipes several shaping operations to get to the final product, adding to labor and energy costs.
- Since they typically get shaped at room temperatures, these pipes may experience an uneven deformation of steel.
- Cold rolling is not as effective as hot rolling in thinning the steel at one go and must be drawn several times.