Mitigation of fatigue cracking on SDSS (Super Duplex Stainless Steel) piping

Super Duplex Stainless Steels have exceptional mechanical and corrosion properties; however, they are a cost-effective solution when operating conditions are tough, despite the precaution that must be taken for fabrication and especially welding.

Most of piping and welding standards and codes are written for carbon steels or austenitic stainless steels; but due to Super Duplex Stainless mixed structure and complex composition, the usual requirements and inspection schemes are not enough to ensure structural integrity.

At INEXSE, we are developing a hands-on expertise based on years of experience, assisting our clients from Engineering Procurement Construction & Commissioning to Operation & Maintenance.

When the need was to mitigate cracking caused by water hammering induced cyclic backwall overload on a SDSS piping; we came up with immediate solution to minimize the cracking by limiting stress and strain.

Common issue is that reinforcing one part is usually make another damage faster. It may be an option to do a reinforcement and choose where the next crack will happen to fix it easily but in practice, when safety is a stake it’s better to find a more effective solution.

Considering that alone, no reinforcement will solve the problem, maybe extend the lifetime only, and that the best solution, that would be to remove the hammering from the process was not an option, we proposed a reinforcement and the implementation of a preloading system:

  • A reinforcement by pad with:
    • Reinforcement design and detailed drawing
    • Welding Procedure Specification for Super Duplex Stainless Steel
    • Cutting, forming and installation procedure
  • A preload the system (and not a reinforcement!)
    • Design and calculation
    • Implementation procedure

Our design driving ideas and constraints were:

  • Avoid any permanent modification of existing piping and structure.
  • Reduce the supplies by:
    • Using standard and similar parts as far as possible.
    • Most of parts manufactured by laser or water jet cutting from a single kind of plate.
  • Reduce the weight by stress and strain optimization
  • Easy preload adjustment.

The turnkey solution is optimized financially and technically, able to handle the operating conditions.

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