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Vanadium sustains the strength of steel at high temperatures for prolonged periods.

Electric Power Generation

For over fifty years of electric power generation, the stability of vanadium carbides at high temperature has formed the basis for the successful operation of many grades of steel used in most of the critical parts of steam turbines and boilers. During this period typical steam temperatures have increased from 480 to 560°C enabling the efficiencies of the plants to increase from 30% to over 43%. Various types of steel have been used for headers, superheater tubes, rotors, casings and blades to resist creep, corrosion and fatigue. Vanadium has been employed in a large proportion of the steels specified in Europe, North America and other parts of the world. Attempts are continuing to increase the efficiency of electric power generation from fossil fuels by increasing steam temperatures and by other methods and in most of these developments vanadium steels play a dominant role.

Steam, superheater tubes and drums

For many years molybdenum-vanadium and chromium-molybdenum-vanadium steels were standard materials for superheater tubes and steam heaters but for a while were superseded by chromium-molybdenum steels.

Today, however, when steam temperatures in some stations are of the order of 580°C, 12% chromium steels with vanadium additions to provide the resistance to creep at high temperature are being adopted. The strength of this steel at high steam temperatures enables the wall thickness and hence the cost to be kept to a minimum. Large steam drums which collect the steam from the boiler tubes are made from plates up to 150 mm in thickness. The steels used contain nickel, chromium and molybdenum to provide corrosion resistance but vanadium is present to give strength at high temperatures. Such drums can involve up to 200 tonnes of steels.

Turbine casings

The casings of turbines have to resist the stresses resulting from the steam pressure at the operating temperature. They are also subject to thermal fatigue and are made as castings. They are commonly made from 0.5% chromium, 0.5% molybdenum, 0.25% vanadium steel where vanadium provides the creep resistance at elevated temperatures

Rotors, Discs and Blades

The turbine rotors, discs and blades of a steam generating plant operate under the most severe conditions having to resist creep, fatigue and corrosion.

Steels containing 1% chromium, 0.5% molybdenum and 0.25% vanadium are widely used for the rotors of high and intermediate pressure turbines because of their high strength and creep resistance. They continue to be used in modern high pressure turbines operating at temperatures up to 565°C and at pressures up to 166 bar. In addition to providing strength and creep resistance to the steels through the carbide precipitates, vanadium has also replaced aluminium for grain refinement. This together with the adoption of vacuum degassing during steelmaking produces cleaner steel with higher fatigue resistance. These developments have led to the manufacture of rotors for high pressure turbines machined from monoblock forgings with considerable economy.

In some countries a steel containing 12% chromium, having higher corrosion resistance, is used for rotor forgings but the steel also contains vanadium to give stability at the high steam temperatures.

Similar 12% chromium steels are used for the turbine blades which have to resist corrosion as well as creep. In low pressure turbines they have to resist erosion from water droplets. In these steels, strength and creep resistance is achieved by vanadium and other alloying elements. The tips of the blades in some large low pressure turbines are subject to particularly severe conditions and inserts of high-speed tool steels containing 0.5% vanadium are used.

In low pressure turbines, operating with steam temperatures below 350°C, corrosion and erosion from water droplets are of greater importance and higher chromium and/or nickel additions are made to rotor steels. These steels also contain vanadium to give the desired heat treatment response.

Transmission towers and poles

Electric power from generating plant is carried across land to towns and industrial areas by copper or aluminium cables supported on a series of steel poles or towers. Many of the transmission routes involve long distance along difficult and remote terrain. For ease, economy of transport and erection, it is important that the towers should be of minimum weight. Vanadium steels having yield strengths 20%

Oil and Gas Production

Vanadium gives strength and low temperature toughness.

The oil and gas industries have for over fifty years continuously offered challenges to the steel industry and more recently to the titanium industry for higher strength materials. Invariably, additional properties are required such as toughness at low temperatures for pipelines laid in arctic regions or special corrosion resistance for lines carrying sour gas.

The greatest developments have taken place in pipeline steels for gas transmission because an increase in strength can enable higher pressures to be used which dramatically reduces the cost of transporting gas. Higher strengths are also important for oil lines to reduce the wall thickness of the pipes and thus to reduce the weight of pipes and the cost of transporting the pipes to site. This is significant in lines stretching for thousands of kilometres.

Where the pipelines operate at low ambient temperatures the steels must be resistant to low temperature brittleness. All steels must be weldable at the highest possible speeds without susceptibility to hydrogen cracking even when welded in regions of high humidity. For pipelines carrying sour gas the steels must be resistant to corrosion by hydrogen sulphide.

Vanadium is used in steels made to specifications involving various combinations of these properties for operation in many types of environment.

Pipelines

Alongside the increasing demand of oil and gas companies for steels having higher strengths, increased low temperature toughness and a capability to be welded at higher speeds, developments have also taken place in steelmaking and rolling which have enabled higher strengths to be attained at lower carbon contents without heat treatment.

The first high strength steels were supplied in the normalised condition and vanadium was added with nitrogen to give a fine grain size and precipitation strengthening.

Special rolling processes which replaced the normalising enabled low carbon steels with increased weldability to be used for pipelines but they required vanadium to maintain the strength of the pipe especially in pipes with thicker walls. Variations have taken place in the pipemaking processes but in both the traditional and new methods vanadium is used to maintain the strength of the pipes.

Vanadium steels were used in most of the major pipelines built in the second half of the 20th century including the Alaskan oil pipeline, the trans-European pipe bringing natural gas from the Russian Arctic to western Europe and the Northern Borders pipeline carrying natural gas from Alberta, Canada to the eastern USA.

Pipes for transport of sour gas

A large proportion of the natural gas coming from below the sea is sour and has to be transported by pipeline to land before the hydrogen sulphide can be removed.

In order to avoid the corrosion which results from hydrogen sulphide in sour gas, lower carbon and manganese contents are used and to compensate for the resulting loss in strength vanadium is added.

Offshore platforms

The legs of offshore platforms are welded from plate steels and in many the strength is achieved by the addition of vanadium.

In platforms built in deep water the weight of the superstructure is of critical importance and extra high strength heat treated vanadium steels are used.

Pipeline Valves and Bends

Valves and bends in pipelines are forged and welded from plates of normalised high strength steels containing vanadium.

Vanadium-titanium Alloy Pipe for Oil and Gas Wells

Vanadium provides the strength in pipes of titanium alloys developed to resist the severe corrosive action of sour gas and oil in some wells in North America

Oil Storage Tanks

Oil storage tanks are made by welding normalised or quenched and tempered steels which depend for their strength on vanadium carbide precipitation.