Corrosion - one of the main challenges

Corrosion is one of the main challenges the offshore renewable energy sector faces. It is a complex issue related to:

  • The focus of current standards and guidelines on lifetimes of less than 15 years
  • Learnings from the offshore oil and gas industry not being implemented
  • Failing systems repeatedly used
  • Problems not occurring directly, but after 2-10 years
  • Insufficient corrosion and material know-how as part the design/project
  • The operator not being the designer, but having to deal with long-term problems

Material needs in marine environments

A parameter for comparing the resistance to pitting in chloride environments is the PRE number (Pitting Resistance Equivalent). The PRE is defined as, in weight-%: PRE = %Cr + 3.3 x %Mo + 16 x %N

For marine applications PRE > 40 is recommended and the following diagram compares the PRE and yield strength for a number of currently used grades.

Performance of stainless grades.jpg

Risks in offshore environments

Splash zone

  • Alternating wet and dry
  • The most critical zone
  • High chloride content can be formed on the surface

Sea spray

  • Chloride deposits
  • Pitting corrosion

Clamps and deposits

  • Tight spaces
  • Crevice corrosion

Immersed

  • Pitting or crevice corrosion

Biofouling

  • Introduces crevices (and corrosion potential)
  • Adds weight
  • Increases friction

Read more about our duplex stainless steels