Detection of thermal damage on vital parts for the aerospace industry

The challenge

High Strength Low Alloy (HSLA) steel is widely used in the aerospace industry for the manufacture of vital parts. Hard-to-detect thermal damage to such parts – incurred during the manufacturing process – can have major and impacting consequences. KLM was looking to provide its engineers with the know-how and tools to effectively detect such damage.

The analysis

HSLA steel (> 200 ksi,=>1400 N/mmÇ2),, also known as HHT (High Heat Treated) steel obtains strength by undergoing several heat treatments at high temperatures. Typically, such steel is used for vital parts in the aerospace industry, including: landing gears, flap carriage assies, fan mid-shaft and cargo door hinges.

The findings

HSLA parts are grinded twice during overhaul. First, there is the pre-grinding that removes defects such as scratches, indents and corrosion. Second, is the grinding of the applied chrome plating. Quality is assured after pre-grinding by nital etch inspection. However, after chrome grinding, no inspection is prescribed to assure acceptable quality.

The solution

Barkhausen Noise inspection assures acceptable quality for chrome plated and grinded HSLA steel parts. KLM was the first airline to start using Barkhausen Noise Analysis to detect thermal damage caused by abusive grinding on chrome plated HSLA steel.

In close collaboration with INNOGRIND, KLM put in place a complete and certified Barkhausen noise inspection training programme for its engineers, comprising:

  • HSLA course – awareness creation of thermal damage on HSLA steel parts.
  • Theoretical Barkhausen noise training – detection of different types of thermal damage.
  • On-the-job-training – hands-on training and interpretation of inspection results.

The result

INNOGRIND’S Barkhausen noise inspection training programme has provided KLM engineers the advantages of a non-destructive, fast, easy and effective inspection method.

Background information

Failure of part was caused by abusive grinding. Abusive grinding results in excessive (local) heat input.

– Softening of the base material (sub) surface

– Reduction of compressive residual stresses (which are applied by shot peening)

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