Success for titanium tubes in chemical applications

Citation

(1999), "Success for titanium tubes in chemical applications", Anti-Corrosion Methods and Materials, Vol. 46 No. 5. https://doi.org/10.1108/acmm.1999.12846eaf.002

Success for titanium tubes in chemical applications

Keywords Titanium, Sandvik, Marine environments

For many years the chemical process industries viewed titanium as too specialist, expensive and hard to fabricate.

However, process developments in the chemical industry have placed ever increasing demands on materials and titanium is now said to be a cost-effective alternative to stainless and other high alloy steels. According to Sandvik it has become a standard construction material in many chemical production plants. Fabrication and welding techniques have been developed so that it is routinely used in a growing number of applications.

Following its decision, in 1996, to target the chemical, petrochemical, plastics, oil and gas processing markets with not only seamless titanium but also its zirconium tubes, AB Sandvik Steel is now claiming significant worldwide gains in market share.

The most recent contract involves the supply of straight lengths and U bent Commercial Grade 2 seamless titanium tubes (Plate 1) for several heat exchangers required for the refurbishment and modification of a PTA plant in the Far East.

Plate 1 An application for titanium tubes in a desalination skid for an offshore platform

Part of a £350,000 contract, the orders were placed by RMF Engineering Ltd, the Sheffield-based specialists in the design and construction of high quality corrosion resistant plant for the chemical and petrochemical industries.

Sandvik operates in a niche market and specialises in the production of seamless, rather than welded, titanium tubing. Although often interchangeable, the same chemical processes which increase demands on materials determine that in some instances seamless tubes and not welded are now specified or will be in the future. This means a significant worldwide and growing requirement for seamless tubes.

In heat exchanger applications, for example, particularly, where chlorinated sea water cooling is involved, titanium tubes are now regularly specified when potential maintenance costs and life cycle cost calculations are taken into account.

Titanium has excellent corrosion resistance in many environments due to its thin but protective oxide film.

The resistance of titanium to sea water is well-known. As opposed to many other materials, titanium is not susceptible to general corrosion or pitting in sea water, nor is it sensitive to the velocity of the water in, for instance, pipe lines. Crevice corrosion of titanium in chloride-containing environments is usually not observed at temperatures below 80°C, independent of chloride concentration.

Solutions containing oxidising metal chlorides can cause severe corrosion in stainless steels. Pitting and stress corrosion cracking are the main causes of failure. Titanium, on the other hand, has a high resistance to oxidising chlorides.

Stress corrosion cracking is seldom observed for titanium, although it can occur in some special environments such as water-free methanol, carbon tetrachloride and trichloroethylene. This can be prevented by adding small amounts of water to the methanol and by the use of inhibitors for the chlorinated hydrocarbons.

Titanium is now regarded as being straightforward to weld using standard techniques such as tungsten and metal inert gas, electron beam, laser and friction welding. The major differences between welding titanium and stainless steel or nickel alloys is the need for heightened cleanliness and shielding with titanium, since the metal must be completely free of any surface contamination to ensure sound, ductile connections. Inert gas shielding is required, on both sides of the weld.

Details available from Sandvik Steel. Tel: +44 (0)1922 728800; Fax: +44 (0)1922 728827; Internet: www.steel.sandvik.com