Evaluation and Development of Alternative Coatings to Reduce
and/or Eliminate Bridging Oxidation, 18-R8239
Inclusive Dates: 07/01/11 – 06/30/12
Background — The primary objective of this project was to
evaluate and develop alternative coatings to avoid or minimize bridging
oxidation. This project addressed bridging oxidation found in the nuclear
industry affecting boiling water reactor (BWR) safety relief valves (SRVs.)
Bridging oxidation is defined as when two mating parts, under a compressive
load, at elevated temperatures, for long periods of time, bridge together due to
an oxidation growth, requiring additional force to separate. The SRV's main
function is to release in the event of an over-pressure scenario. Failure to
open can cause a catastrophic failure.
Approach — By developing a simulated BWR environment to create bridging oxidation and by creating standardized mechanical testing procedures, one can quantify bridging oxidation to compare the materials currently used to alternative coatings that will reduce or negate the effects of bridging oxidation. The technical approach for this project was to design and develop test coupons and a mechanical test fixture that would quantify the apparent "adhesion" associated with the oxidation growth between the pilot disc and seat and then to assess the performance of different coatings and configurations in an attempt to minimize the effects of the bridging oxide in the overall performance of the SRV when in service.
Accomplishments — This project met three technical challenges:
- successfully demonstrated the ability to generate bridging oxidation bonding,
- successfully measured the forces required to separate the adhesion created by the bridging oxidation bonding,
- successfully developed an alternative coating, CrSiCN, that when applied to the mating surfaces of test coupons, no bridging oxidation bonding occurred.
The CrSiCN coating is a candidate for marketing as a true oxidation-resistant coating, viable for application in the BWR nuclear environment. From a business standpoint, the ability to generate, quantify, and eliminate bridging oxidation bonding has set up the next phase of work, which is to qualify the improved process on BWR SRVs in the field. The results from this project have been presented to the Tennessee Valley Authority, a user of BWR SRVs, of which SwRI has been invited to present the results at its industry working group meeting in January 2013. In addition SwRI has submitted, and has been accepted to present the results at the annual 2013 TMS Meeting in March.