Piston rings are to be diagnosed at regular intervals on the basis of the wear pattern. Piston rings have to be replaced after they have been use for time periods given in the maintenance schedule. Replacement will also be necessary if interim checking reveals damage to running surface or excessive clearances.

Different Piston Rings:
The rings being in use are compression rings with chromium-plated, Plasma-coated or (the most recent solution) chromium/ceramic-coated running surfaces, and chromium-plated oil scraper rings.

Piston rings for MAN B&W 9L 58/64
Compressor Ring

Running Surface
Groove 1
Packing ring
Groove 2
Tapper ring
Groove 3
Tapper ring
Oil scraper ring

Groove 4
Oil scraper ring

Wear appearance of plasma-coated, chrome-plated or chromium/ceramic-coated piston rings
Due to its shape, the running face of new compression rings does not have contact across its full width but only the width of the actual contact surface A. With the progress of wear, the actual contact surface width will increase.

Figure 1. Running face of plasma-coated and chrome-plated piston rings (time in use > 1000 hrs)