Metal Face Seal Fitting Field Study
Multi Mate-Demate Record
This report details a Multi mate/demate field study at Lawrence Livermore National Laboratory. Over six years in service, this fitting was mate/demated 1557 times and was still working effectively when decommissioned. This evaluation shows the direct cost savings by avoiding the replacement of fittings that no longer passed leak check in this crystal growth equipment. The opportunity cost of having the system down for maintenance in a production environment is a much greater cost. The system maintenance hours avoided are tabulated below.
The Omnisafe fitting mounted on a Crystal Growth Chamber was exposed to hot (200C) hydrogen fluoride gas for a four hour run daily, for six years without a single failure. The fitting was mate/demated once per day.
- Standard 1/2“ metal face seal fittings without torque elimination typically lasted 15 mate/demate cycles (three weeks) in this environment.
- Over the system life (311 weeks) in this case, LLNL avoided approximately 103 fitting replacement, maintenance events.
- In quantities of 100 the material cost for standard 1/2” fittings is estimated at $36.75 * 100 = $3,675
- The labor included prepping the system, cutting off the old glands, decontaminating the old parts, prepping the ends, orbitally welding on new glands, and leak checking the system. The whole process took 4-6 hours. The labor cost was $500 approximately plus the decontamination cost.
- Total direct cost per maintenance event: $536.
- Total direct cost savings annually was: $8,933.
- Total direct cost savings over the system life: $53,600.
- The value added in increased system availability was 83 hours annually.
- The additional production time made available was 498 hours over the system life, when considering the maintenance events that were avoided.
Conclusion
In terms of sealing surface preservation and the ability to pass leak check, this field test showed the Omnisafe fitting was over 100 times better than the legacy metal face seal fitting. In truth, since there is no galling during Omnisafe seal formation, the torroidal seal may last indefinitely. The $53,600 savings is a very conservative number since it does not include the production opportunity gained by avoiding maintenance.
If the opportunity cost is $40K per 8 hr shift in a semiconductor fab then this fitting’s longevity would have saved over $19M in avoided down-time cost over 6 years. Paredo analysis of fitting failures in the industry would indicate that 95% of the cases involve problems with the sealing surfaces. Omnisafe enables gas system engineers to avoid these fitting failures. This represents significant cost reduction.