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Compressor : Hitachi

Hitachi

The following is an introduction to diagnosis technologies used in the maintenance process.

Technology for diagnosing remaining air cooler service life

Problems associated with air coolers can have serious consequences for compressors themselves, and it is essential that periodic maintenance and planned upgrades be implemented.

Based on past air cooler overhaul results, we know that most problems are due to immersion in coolant water and the resulting corrosion damage to ordinary steel. Damage to shells and baffle plates have a particularly significant effect on air cooler service life.

The corrosion visible on the inner surface of the shell and on the baffle plates advances as the number of operating years and operating time increases, and it is typical for localized corrosion to occur as a randomly occurring phenomenon along with contaminant adhesion, peeling of the rust-proof coating, nonmetallic inclusions, etc.

Another factor that causes rust is the surface condition of the material, coolant water quality, flow rates, temperature, and other factors that cannot always be characterized. Moreover, since these effects are so complex, it is extremely difficult to assess the degree of corrosion.

That is why it is so important to collect field data about corrosion based on cumulative measurements taken over time and to verify these against corrosion prediction master curves that we have developed. In doing so, we can assess the maximum amount of metal lost in the shell and baffle plates based on ultrasonic shell wall thickness measurements.

Photograph: Air cooler
View of air cooler

Predictive master curve

Image: Predictive master curve graph

  • Corrosion service life coefficient calculation using various parameters (measured wall thickness, number of scheduled inspections, operating years, etc.)
  • Find intersection point t1 with estimated maximum reduced wall thickness
  • Shift curve up to t1 and find the intersection t2 with the limit wall thickness guideline
  • Estimated remaining service life t= t2-t1