Bosses at Tata Steel have confirmed they are to begin the process off its Hartlepool site.
Two of the pipe mills, in Brenda Road, Hartlepool - where 500 people are employed - will be put up for sale, along with the South Yorkshire-based Speciality Steels business.
Hartlepool’s 20-inch Tube Mill is not part of the deal
Koushik Chatterjee, Tata’s group executive director said: “Both of these operations are largely independent of the strip products supply chain with their own specific characteristics.
“Tata Steel UK has already received interest from several bidders for Speciality Steels and the pipe mills. In each case and a formal process will be commencing shortly.”
The announcement came as the firm announced it has entered into talks with strategic players in the steel industry to explore the feasibility of a potential joint venture for the rest of the troubled company.
The talks are at a preliminary stage and Tata said there can be no certainty of a transaction.
The Community union said the move continued uncertainty for thousands of steelworkers and their families.
Tata said there had been seven expressions of interest in buying its business after it announced in March that it was selling its loss making UK assets.
The board, meeting in Mumbai, said it had decided to look at “alternative and more sustainable” solutions and talks have started with companies to explore a potential joint venture.
Chatterjee said: “We have initiated conversations for a strategic collaboration for our European business. A potential strategic combination of strip product businesses offers the best prospects to create a premium, world-class strip steel business with the scale and scope to compete successfully on the global stage.
“It is too early to give any assurances about the success of these talks.
“Such success, especially the inclusion of the UK business in the potential joint venture, would depend on several issues including finding a suitable outcome for the British Steel Pension Scheme, successful discussions with the UK trade unions and the delivery of policy initiatives and other support from the Governments of the UK and Wales.”
He added: “We will continue to communicate with our employees and inform and consult both works councils and trade unions as these discussions develop.”
Roy Rickhuss, general secretary of Community, said: “The current status of the sales process is unclear and this will be frustrating for our members, and perhaps even the bidders.
“This new approach means that uncertainty will continue for thousands of steelworkers and their families.