Differences between hot-rolled and hot-expanded seamless tubes

Differences in production processes:

‌Hot-rolled steel tube is a steel pipe made by high-temperature heating, rolling and cooling, which has the characteristics of high precision and high toughness. The manufacturing process of hot-rolled seamless tube is mainly divided into three steps: heating, rolling and cooling. The heating part makes the steel billet reach a suitable rolling temperature, the rolling part is to press the steel billet into the required shape and size, and the cooling part is to cool the finished steel pipe to room temperature in the air at a controlled speed.

Hot expansion is a processing method for steel tubes, which is to process small-diameter steel tubes into large-diameter steel tubes. The mechanical properties of hot-expanded steel tubes are slightly worse than those of hot-rolled steel tubes. Hot-expanded steel tubes are a steel pipe made by high-temperature heating and diameter expansion, which has the advantage of high inner diameter accuracy. The manufacturing process of hot-expanded seamless tubes is to expand the end of the formed steel pipe at high temperature, and then undergo a series of processing procedures. The manufacturing process of hot-expanded steel tubes mainly has five steps: billet processing, billet physical treatment, local forced heating, pipe end diameter expansion and overall annealing.

Product characteristics of hot-rolled seamless tubes and hot-expanded seamless tubes:

1. Precision: The hot-rolled steel tube has higher precision, the interior is relatively tight, and the inner diameter precision can reach H9~H11 level; while the surface of the hot-expanded steel pipe is relatively rough and the interior is relatively loose, so it is suitable for high temperature and high pressure environments.
2. Toughness: The hot-rolled steel tube has better toughness and can withstand certain deformation and impact, while the hot-expanded steel tube has poor toughness, and the inner and outer surfaces are prone to cracking and deformation.
3. Welding performance: The hot-rolled steel tube has better welding performance and can meet various processing requirements; while the inner surface of the hot-expanded steel tube is relatively smooth and is not suitable for line welding.

Production efficiency:
The production efficiency of hot expansion is relatively low, and each pipe needs to be processed several times, and the cost is relatively high; while the production efficiency of hot rolling is high, and batch production can be achieved, and the cost is relatively low.

Application scenarios:
1. Hot-rolled steel tubes are suitable for manufacturing various structural parts, mechanical parts and pipelines. The steel pipe specifications that can be manufactured are small, and the maximum diameter generally does not exceed 508 mm.

2. Hot-expanded steel tubes are suitable for pipes, cylinders and various precision mechanical parts. They have high inner diameter accuracy and are suitable for various processing requirements that require high precision. Hot-expanded pipes are suitable for manufacturing high-temperature and high-pressure fields such as aircraft engines, aircraft, nuclear power plants, and chemical equipment.

Cost Comparison:

The overall production cost of hot-expanded seamless steel pipes is significantly higher than that of ordinary hot-rolled seamless steel pipes. Hot-expanded seamless steel pipes are produced by further processing ordinary hot-rolled seamless steel pipes as the "mother pipe." This means it includes the entire production cost of ordinary seamless steel pipes, plus the additional costs of subsequent processes.

Why are more Expensive Hot-expanded Pipes needed?

Technical Limitations: 

Traditional hot-rolled seamless steel pipe processes have an upper limit on the economic diameter (usually below Φ426mm). To produce seamless pipes with diameters larger than this specification, directly using larger steel billets for piercing and rolling would require exponentially higher equipment capacity (rolling mill, piercing mill), resulting in extremely high equipment investment and energy consumption, making it uneconomical.

Advantages of Hot-Expanded Pipes: 

The hot-expansion process cleverly circumvents this limitation. It uses relatively small-diameter ordinary hot-rolled seamless steel pipes as the mother pipe, and expands the diameter through heating to produce large-diameter seamless pipes from Φ406mm to Φ1220mm or even larger.

How to Choose?

Hot-expanded pipes supplement and extend the range of specifications for hot-rolled seamless pipes, mainly used for large and extra-large diameter applications. When the required specifications are within the range of ordinary hot-rolled seamless pipes, always choose ordinary hot-rolled pipes because they are more economical and have more stable quality; only when the required diameter is very large and welded pipes cannot be accepted (such as when pressure bearing or extremely high reliability requirements are met) should hot-expanded seamless pipes be selected.

Conclusion:

Due to differences in process and product characteristics, hot-rolled seamless tubes and hot-expanded seamless tubes are suitable for different scenarios. Although the inner and outer diameter accuracy of hot-rolled steel tubes is slightly worse than that of hot-expanded steel tubes, they have better toughness and welding performance, lower manufacturing costs and a wide range of uses; while the inner diameter accuracy of hot-expanded steel tubes is higher, which is suitable for manufacturing high-temperature and high-pressure fields such as aircraft engines, aircraft, nuclear power plants, and chemical equipment.

Read more: Carbon steel tube material and use or Cold rolled vs. Hot rolled