Design and Qualification Testing of Anvil Fig. 3306N Hydraulic Snubbers

The Fig 3306N Hydraulic Snubber was designed to meet the performance requirements of the next generation of Nuclear Power Plants. Specifically, the Fig. 3306N provides the following upgrades to our existing ASME designed Fig 200N Snubber:

  1. Compactness. The space envelope required for the Fig. 3306N is less than half that required for the Fig. 200N. The new plants will be more compact than the older ones and will require equipment that is more compact
  2. Extended Service Life. The Fig. 3306N is designed to operate for 25 years before it has to be rebuilt compared to the 7 year service life of the standard Fig. 200N. (We have existing snubber configurations that have a longer life, but they are not designed to the ASME Code.) New plants require the longer service in order to minimize maintenance time and reduce down time during scheduled outages.
  3. Vibration Mitigation. The existing Nuclear Power Plants have become aware that new piping configurations have caused vibrations in their piping, which in turn have caused excessive wear on their existing snubbers. New Plants will require that snubbers be less sensitive to the effects of vibrations and if possible help to mitigate the vibration. In service testing of the Fig. 3306N has shown that its new seal configuration provides for extended service in very high vibration environments and provides for a measure of vibration mitigation. (One snubber in the Catawba Plant greatly reduced the pipe vibration and lasted for 500 million cycles before it had to be rebuilt and has been installed for over one billion cycles).

The qualification testing of the Fig. 3306N snubbers was performed to the requirements of ASME QME-1 Section QDR. This code replaces the General Electric qualification document 21A3502, which had been the snubber qualification standard for the past 30 years. ASME QME-1 Section QDR includes all of the General Electric requirements and the following additional tests:

  1. 5 additional bleed rate tests to verify performance at various loads;
  2. Room temperature and 200°F dynamic tests from 3 to 33 Hz. at 2 additional piston positions to determine average spring rates at these positions. (This is important for single ended cylinders because their average spring rate is affected by the piston position.);
  3. 200°F Level D dynamic tests at 2 additional piston positions.

The additional dynamic tests significantly increased the total number of cycles that were required for testing. All snubbers passed the qualification tests.

For more information of Anvil Figure 3306N Snubbers please call Frank Birch Product Engineering Manager at 401-886-3031.

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