Eddy Current NDT

Inspecting for Cracks in Austenitic Stainless Steel Welds

Published on 21st July 2020

Inspecting for Cracks in Austenitic Stainless Steel Welds

Source: https://www.eddyfi.com/en/appnote/inspecting-for-cracks-in-austenitic-stainless-steel-welds

Stainless steel and INCONEL welds are often encountered in the extreme conditions common in the power generation industry because of their good resistance to heat, to corrosion, and to cracking. However, these welds pose unique inspection challenges.

The Challenge

Defect small cracks in 304 and 316 austenitic stainless steel and INCONEL® welds.

304 and 316 austenitic stainless steels and INCONEL (referred to, here, as austenitic alloys) are corrosion and oxidation resistant because they contain chromium, which forms a self-healing protective film on their surface. They are also the most easily weldable of austenitic alloys, so they are therefore widely used in mission-critical assets of the power generation industry. Austenitic alloys are, however, not impervious to cracking, but the assets where they are used usually have a very low tolerance to leaks, whether it be for security (radiation) or efficiency reasons. It is therefore important to accurately detect the presence of cracks in austenitic alloy welds and characterize their severity. Current weld inspection techniques include PT, MT, and pencil ECT probes, and have several limitations:

  • They are time consuming. Welds can be very long, so an improved solution must be faster.
  • They are highly user dependent. To yield consistent results, an improved solution must not be.
  • They may require extensive preinspection and post-inspection surface preparation with chemical products.
  • They offer limited traceability, which is crucial for auditing and to monitor the evolution of cracks.

Austenitic alloys usually respond well to electromagnetic inspection techniques, but using them in this type of application poses certain problems:

  • Target defects can be very short (length ≈ 2 mm [0.079 in] or less).
  • Crack severity must be assessed.
  • Welds can be rough, causing premature wear in common surface probes.

The Solution

Adapted, rugged ECA technology that can take on welds and detect small cracks.