Nickel alloy addresses the sour gas challenge

Peter Bamforth, lead technical manager for Outokumpu Europe, outlines the advantages of Ultra Alloy 825 for the oil and gas industry, especially its good resistance to sulphur containing environments where it has superior resistance to hydrogen and hydrogen sulphide induced cracking.

Natural gas is now playing an increasingly important role in the global energy mix. However, a large proportion of the world’s natural gas reserves is ‘sour’ gas containing significant levels of hydrogen sulphide H2S and carbon dioxide (CO2). In fact, in the Middle East, sour gas comprises around 60% of the total gas reserves. The presence of H2S has, in the past, made exploitation of sour gas resources challenging due to the tendency for it to cause corrosion and sulphide stress corrosion cracking of steels, especially in pipelines.

In addition to the corrosive environmental conditions, sour gas is usually found at temperatures up to 260°C and high pressures up to 1,700 bar. This makes material selection a critical factor in sour gas operations. The challenge is to find the ideal combination of corrosion resistance and strength to ensure cost-effective operation over a typical 30-year service life. The material of choice has evolved from carbon steels to duplex (austenitic-ferritic) stainless steels and now to nickel alloys such as Outokumpu’s Ultra Alloy 825.

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