Spring material: Selection matters

For structures and equipment operating in harsh environments, springs and spring fasteners must be able to withstand different types of extreme conditions including underwater, outdoors and very high or low temperatures, as global spring company Lee Spring explains

Challenging working conditions can be encountered across various industry sectors, such as aerospace, valve manufacturing, offshore and sub-sea industries, medical, power station and nuclear industry, turbine manufacture and general engineering. Springs and fasteners are often vital components of various equipment and therefore must be designed to withstand the application-specific conditions.

"Working in a harsh environment could mean anything from equipment required underwater, battling saltwater corrosion or contact with 'sour' gas from drilling down under the sea bed, to 35,000 feet up in the air contending with high wind speeds and low temperatures", says Nick Lungley, applications engineer at Lee Spring. "An offshore application requires equipment that can brave the elements, and some manufacturing or furnace applications involve extreme heat or cold, while some will require equipment to be subject to highly corrosive substances." Custom engineering in spring design can help to ensure that the spring or fastener has been manufactured to suit the specific requirement, choosing from a wide variety of advanced spring materials.

Alloys (metals made up of more than one type of metal) are often used as they offer a higher resistance to corrosion. Lee Spring, offers high performance nickel and cobalt 'superalloys', which provide good mechanical strength as well as resistance to corrosion, oxidation and deforming at high temperatures or under extreme pressure.

Equipment used in sub-sea or offshore applications is subject to the risk of corrosion from various elements including salt water, wind and rain, so springs required for these applications can be made using corrosion resistant nickel based and cobalt alloys, including MP35N, Monel, Inconel, Nimonic, Hastelloy and Elgiloy.

The nickel-cobalt alloy MP35N, which consists of nickel and cobalt, is resistant to hydrogen sulphide, salt water and mineral acids, so is well suited to marine and sub-sea applications where salt water can have a highly corrosive effect on most metals. The nickel based alloy Monel incorporates copper and iron and is corrosion resistant, as well as acid resistant, so is suitable for marine applications as well as applications involving acids and highly corrosive substances.

"The selection of the correct material for a specific, demanding application is critical", says Darren Eyre, technical specialist at Lee Spring. "For instance, stainless steel is a tough and corrosion resistant alloy, but does not offer the properties required to withstand extreme heat and is likely to distort at a high temperature. It is therefore important to clearly understand the environment it is likely to be used in." Inconel alloys, which are available in different grades (600, X-750 and 718), are suitable for valves, pumps or actuators, or applications involving high pressure and high temperatures, such as in nuclear power stations or drilling on offshore platforms.

Also corrosion resistant and suitable for high temperature and high pressure applications are Nimonic and Hastelloy alloys.

Lee Spring offers custom engineering in spring design and a range of materials, available up to 19mm diameter, alloys and nickel and cobalt superalloys including Inconel, Nimonic, Hastelloy, Monel, Elgiloy and MP35N. Other alloys available include stainless steel, phosphor bronze and beryllium copper.