Cold-Rolling And Hot-Rolling Steel Pipe

Steel products vary in grade, shape, size, specification, and finish, many of which have unique properties. Steel pipe manufacturing has a significant impact on how it will be used across a wide range of industries. For prefabricated steel products, cold-rolled and hot-rolled determines the useability of steel pipe and make up the key differences between the two end products. Steel with differing grades or specifications can be manufactured through either hot-rolled or cold-rolled processes.

Hot-Rolled Steel Manufacturing Process

Hot Rolled Steel Manufactured

Hot-Rolling steel is the process of steel manufacturing through heat, generally separated into low, medium, and high-pressure boiler steel pipes. Hot-rolled steel has been roll-pressed at high temperatures of over 1,700 degrees which rises above re-crystallization threshold temperatures for most steel. Through this process, the steel is easier to form and work with. Manufacturing begins with a large, rectangular piece of metal called a billet. This billet is heated and sent over to be flattened into a roll. Keeping it at a high temperature, it is run (at high speeds) through a series of rollers until the desired dimensions are reached. Hot-rolled steel is cooled after it has been processed and will shrink slightly while it cools, meaning its final form is not as precise as cold-rolling is.

Ex. Hot-Rolling Seamless Steel Pipe Process

Round Billet Heating Perforation Extrusion Sizing Hot Rolling Cooling Straightening Hydrostatic Test Signing Storage

How To Identify Hot-Rolled Steel

  • Scaled Surface - cooling from extreme temperatures
  • Slightly Rounded Edges Or Corners - due to cooling process and shrinkage
  • Distortions - due to cooling process and shrinkage

Cold-Rolled Steel Manufacturing Process

Cold-rolling steel is a process done near or at room temperature, but essentially is hot-rolled steel that has been taken further into processing. After the steel has been hot-rolled and cooled, it is re-rolled at room temperature for better specification of dimensions and higher quality surface qualities. Technically speaking, cold-rolled refers to sheets that undergo compression between rollers. However, cold-roll loosely describes a wide range of finishing processes in the steel industry, including turning, grinding, and polishing (furthering a hot-rolled item into a better and more refined end product).

Ex. Cold-Rolling Seamless Steel Pipe Process

Round Billet Heating Perforation Annealing Pickling Anoint Cold Rolling Heating Straightening Hydrostatic Test Signing Storage

How To Identify Cold-Rolled Steel

  • Finished Surface With Close Tolerances
  • Oily Smooth Surface
  • Uniformity And Straightness (Noticeable For Tubing)
  • True Sizing, Defined Edges
Cold Rolled Steel Manufacturing

Key Differences Between Cold-Rolled Pipe And Hot-Rolled Pipe

Hot-Rolled Cold-Rolled
low, medium, high-pressure boiler steel pipe, stainless steel pipe, oil cracking pipe, geological steel pipe, and other low, medium pressure boiler tube, high-pressure boiler tube, alloy steel pipe, stainless steel pipe, and oil cracking tube, alloy thin wall steel tube, thin-walled stainless steel pipe, and special-shaped steel tube
Does Not Allow Local Buckling Allows Local Buckling (Bending Bearing Capacity)
Distribution Of Residual Stress Is Film Type Distribution Of Residual Stress Is Bending
Higher Free Torsional Rigidity (Better Torsion Resistance) Lower Free Torsional Rigidity
Less Control Over End Result, Lower Dimensional Accuracy High Dimensional Accuracy
Lower Quality Surface Characteristics Smoother, Oily/Greasy Surface Characteristics, Sharp Edges
High Temperature Process, Then Cool Down (Less Control Over Shape) Room Temperature Process Furthering Hot-Rolling (More Control Over Shape)
Highly Used In Agricultural Industry Used For More Technically Precise Applications (Aesthetics)
Cheaper More Expensive (Stronger Properties)

Cold Rolled Steel Fence Pipe Manufacturing Gallery
Cold Rolled Steel Fence Pipe Manufacturing Gallery
Cold Rolled Steel Fence Pipe Manufacturing Gallery

Benefits Of Cold-Rolled Steel: Summary

Greater pressure is required to roll and form steel at room temperature or during the cold-rolling process. Manipulating steel below the recrystallization threshold offers several benefits.

Cold-Rolled Steel Strength

Significantly stronger than hot-rolled steel, cold-rolled steel is compressed by rollers at room temperature, which allows the steel to become stronger through strain hardening. Typically, cold-rolled steel is about 20% stronger than hot-rolled steel.

Tolerances Of Cold-Rolled Steel

The word "tolerance" in metalworking refers to the overall thickness of the metal material. Hot-rolled steel is typically thicker, while cold-rolled steel is thinner without comprising the strength. Because of this, cold-rolled steel has tighter tolerances that are unbeatable.

A Better Surface Finish

Cold-rolled steel has an improved, smooth surface compared to hot-rolled steel. Easy to differentiate from hot-rolled steel, cold-rolled steel has a smooth and often greasy or oily finish and fewer surface imperfections. More suitable for certain application, cold-rolled steel is often used because it is aesthetically nicer.