Cold Rolled Steel Pipe Manufacturing

Nov 24, 2017

What are commonly used heat treatments, purposes and scope of application of steel pipes in cold drawn and cold rolled production?

Heat treatment is an important part in cold drawing and cold rolling of steel pipes. During the production process, heat treatment of steel pipes can be classified into tube billets heat treatment, intermediate tube heat treatment and finished tube heat treatment according to the process. Methods, purposes and scope of application of heat treatment for steel pipes are as the following table.

Heat treatment	Heating temperature	Purposes	Suitable steel	Scope of application
Full annealing	Above Ac3 From 20 to 40℃	Refining grains, eliminating internal stress, network and Widmannstatten structures and reducing hardnes	Hyposteel	Heat treatment of tube billets and finished pipes
Partial annealing	From Ac1 to Ac3 From780 to 800℃ From Ac1 to Acm From750 to 770℃	Improving dispersion of pearlite, eliminating internal stress, preventing decarburization and adopting slow cooling rate can obtain spherical pearlite	For hyper-eutectoid steel	Intermediate heat treatment, finished pipe heat treatment and spheroidizing heat treatment
Recrystallization annealing	Ac1 From 600 to 700℃	Eliminating internal stress and work hardening, reducing hardness and restoring plasticity	All kinds of carbon steel and low alloy steel	Intermediate heat treatment
Normalizing	Above Ac3 From 30 to 50℃	Improving the machinability of mild steel and mechanical properties, refining austenite grains and eliminating net carbide	Hyposteel	Finished pipe heat treatment
Quenching		Eliminating work hardening and internal stress		Intermediate heat treatment and finished pipe heat treatment for stainless steel pipes
Quenching and high temperature tempering	Normalizing and high temperature tempering and annealing and tempering	Eliminating internal stress, improving toughness of the material and obtaining high strength and hardness	Low alloy structural steel	Finished pipe heat treatment

What are the purpose and methods of pickling in the processing of cold-rolled steel pipes?
The oxide scale on the inner and outer surfaces of pipe billets should be removed before the cold drawn and cold roll processes. Methods of removing the oxide scale include mechanical methods such as shot blasting and polishing, chemical methods and electrochemical methods. The pickling method is used for removing the oxide scale on the surface of cold drawn and cold roll steel pipes. Pickling methods include sulfuric acid pickling, hydrochloric acid pickling, mixed acid pickling, hydrofluoric acid pickling and alkali-acid pickling. Sulfuric acid pickling is one of the most widely used methods. Sulfuric acid pickling is usually adopted for carbon steel and low alloy structural steel which don’t have special requirements.