We at Chemipetro supply pipe flanges for the petrochemical industry in a range of resistant alloys, for example Duplex, Super Duplex and 6% Molybdenum (6Mo, or Moly 6).

These alloys are highly resistant to pitting, chloride corrosion and stress cracking, and offer excellent weldability and impact resistance. Duplex and Moly 6 pipe fittings are often used in the same installation, as they are highly compatible.

However, marine environments create particularly corrosive conditions for pipe flanges, which can defy even the most resistant of alloys. This was proved after the installation of the Sleipner A North Sea oil platform, in 1992/93. At the time, stainless steel alloys like austenitic molybdenum and super duplex were being widely deployed on seawater piping systems. For this reason, Sleipner A was fitted with 6Mo pipe fittings and 25Cr super duplex valves on the firewater piping system.

These alloys were qualified for use in seawater systems at a temperature range of 30 – 53 degrees celsius, which at the time was thought to be more than adequate.

However, just 18 months after installation, extensive leaks were discovered in sealed areas around flanges, valve components and threaded pipe fittings. This had been observed in other platforms. It was discovered that although the flanges performed well within the established temperature range, peaks above or below this had a catalytic effect on corrosion rates.

The answer was to fit a new galvanic resistor system to the platform, to withhold corrosion at extreme temperatures. Studies 10 years later show this is a highly efficient system, minimising further corrosion of flanges and pipe fittings.