Steel tolerates corrosive heat exchanger use

A Sandvik Materials Technology UK product story

Edited by the Engineeringtalk editorial team May 1, 2007

Sandvik SAF 2707 HD steel has been developed to meet industry demands for higher operating temperatures and longer run times in critical heat exchanger applications

A new hyper-duplex stainless steel, designed and developed to increase operating performance and extend service life in severely corrosive heat exchanger applications, has been launched by Sandvik.

Sandvik SAF 2707 HD steel is aimed particularly at the chemical, petrochemical and refinery industries.

It has been developed to meet industry demands for higher operating temperatures and longer run times in critical heat exchanger applications, whilst maintaining the reliability, safety and performance of the equipment.

In order to verify Sandvik SAF 2707 HD and gain industrial reference information, heat exchanger tubes have been extensively evaluated, over periods of up to three years, in a variety of refinery applications.

In particular and in a joint project with a major refiner in the US, there is evidence of increased operating reliability and uptime benefits of using the new grade.

Applications in Europe and the Middle East, under a variety of operating and corrosion conditions, have generated similar positive feedback.

At the end of 2003, in the US oil refinery application, a complete tube bundle was retubed with hyper-duplex Sandvik SAF 2707 HD in a top pump-around exchanger in an atmospheric distillation unit.

The previous carbon tubes had a life expectancy of around nine months but difficulties had been caused by chloride attacks and increased corrosivity from a greater use of lower quality crude oils.

Some upgrading of the metallurgy to the super-duplex grade Sandvik SAF 2507 had extended tube life but even this grade was considered to be operating very close to its performance limits in this application.

After three years, the Sandvik SAF 2707 HD tubes have performed without problems.

Sandvik SAF 2707 HD is a high-alloy duplex stainless steel, specially developed for service in highly corrosive conditions, such as seawater-cooled heat exchangers.

It is particularly suited to aggressive, acidic, chloride-containing environments and displays excellent resistance to pitting and crevice corrosion, stress corrosion cracking and general corrosion.

At the same time, it has high mechanical strength and good weldability.

The superior properties of the new steel, compared with other duplex stainless steels, make it an alternative to super austenitic steels and nickel-base alloys.

Modern duplex and super-duplex stainless steels for heat exchangers have been developed for their high resistance to pitting and crevice corrosion.

Sandvik has used the knowledge gained from producing its previous duplex grades to introduce a higher level of performance into the new grade.

The generally accepted index for comparing resistance to pitting and crevice corrosion is the PRE value.

Sandvik SAF 2707 HD has a nominal PRE value of 49.