Obtaining proper coatings to achieve acceptable rod life depends largely on (1) good communications between user and coating vendor, (2) selection of qualified coating facilities, and (3) adherence to appropriate quality control standards.
Potential areas which may lead to unacceptable rod repair include:
• Rod base metal metallurgy not known. Previous coating history unknown.
• Improperly selected coating for actual operating conditions.
• Inadequate quality control prior to and/or during coating application.
• Poor compatibility of coating with packing material.
• Incorrect or incomplete specification of rod area to be coated.
• Finished rod dimensions and tolerances not specified.
• Improper taper at ends of coating.
• Desired surface finish not stated.
• Excessive coating thickness required to build up badly worn or gouged rod.
• Poor bond strength between undercoat, if any, and base metal.
Figure 800-18 (Part I) includes basic operating, design, dimensional, and metallurgical information essential to the coating vendor. This section should be carefully completed by the Purchaser and included with each piston rod sent to a reconditioning shop. Purchase orders for coating work should require that Part II of Figure 800-18 be completed by the coating vendor after coating work is complete. The completed figure, specifying the as-finished coating condition, should then be returned with the reconditioned rod and become part of the compressor maintenance records. Any refinishing performed after the rod has been in service should be noted in Part III of Figure 800-18. This information will assist in evaluating the extension of service life afforded by the coating process.