Ceramic Coating Basics2 min read

Coating Tests with Missed Visits: Report an Interval for the Failure Time

Report coating failure between the last passing and first failing inspection when the exact event time was not observed.

Updated · NANOLAB Knowledge

Editorial illustration: A Practical Quality-Control Process for Ceramic Coating
Editorial illustration

If a coating passes an inspection at month four and fails the agreed criterion at month seven, the test has not observed an exact seven-month failure time. It has located the event within an interval.

Keep both bounds

Record the last passing inspection and first failing inspection, including their actual dates. In the example, failure occurred after month four and by month seven, assuming the endpoint represents a persistent failure process. Do not replace that interval with its midpoint without stating and justifying the modelling assumption.

Distinguish missing visits from passing visits

Record Meaning
Pass at month four Criterion met at that observation
Missed month-five visit No observation
Fail at month seven Criterion not met by that observation

Choose analysis suited to the data

NIST describes interval-censored data as cases where failure is known only within a time interval. Use a method that accommodates that structure when estimating durability distributions. A specimen still passing at the end of follow-up supplies a different kind of incomplete lifetime information.

Preserve the endpoint definition

Some surface observations fluctuate with contamination or cleaning. If the criterion can recover, decide whether the study measures first failure, sustained failure or repeated condition states. Record maintenance events alongside inspections. A clear timeline prevents missed visits from creating false precision and makes comparisons between products with different inspection schedules more defensible.

Technical references

The sources below support the stated concepts or describe their own methods. The worked scenarios are editorial examples, not NANOLAB test results.

Ask NANOLAB about your surface and intended use. For application and care, use the current instructions for the exact product.