2021 RETA Breeze March-April

so that it does not experience vibrations along its long axis, but rather in the axial or “thrust” direction loads the threads in compression and tension instead of bending. 5. Support the unsupported end to eliminate the cantilever stress on the assembly. Care must be taken so that the support mechanismdoes not apply stress to the assembly but still provides as rigid of a support structure as the opposite end does. The entire assembly must move as a single unit when vibration is present. This solution would be very difficult to achieve considering the location of the assembly and the lack of a good place to tie in a new support structure. While preparing this report, I reached out to the Maintenance Manager at the facility to follow up on how the solutions they had applied were performing. As stated above, the results look promising, they have experienced no additional failures on the assemblies that have been upgraded. I would recommend that a survey of the remaining assemblies be done, and the upgrade applied to them proactively. Ideally this will prevent an ammonia release in the future due to an issue that will inevitably occur on them if left as is. It is my hope that the information contained above is of value to all involved parties, both to provide assurance that the cause of failure has been identified, and that, if implemented, the solutions provided will give peace of mind that they will not experience continued failures of this type.

Summary:

or eliminate the cantilever effect, or to change the resonant frequencies of the assembly, either of which will eliminate the stress that the threaded connection experiences: 1. Shorten the length of the assembly. This will raise the resonant frequency of the assembly, ideally beyond any frequency that the compressor can produce. 2. Remove as much weight as possible from the unsupported end of the assembly. This will raise the resonant frequency and lower the inertia of the unsup- ported end, which will in turn reduce vibrational stress on the thread joint at the supported end. 3. Install an elbow or tee close to

I would recommend that a survey of the remaining assemblies be done, and the upgrade applied to them proactively.

attachment point. This measure will have the effect of dividing the overall length of the assembly into 2 shorter parts that are at right angles to each other, reducing the stress applied to the threads on the supported end of the assembly. 4. Orient the cantilever arm so that

it is perpendicular to the rotating elements of the

the attachment end of the assembly to reconfigure the piping so that the cantilever arm is perpendicular to the

machine. Most of the vibration of the rotating elements of a screw compressor is radial in nature. Orienting the arm of the assembly

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