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A welded bonnet valve will only leak through the bonnet if the weld
has a crack. In isolated cases, this will happen at the start/stop
of a weld. Porosity in the weld will remain masked during factory
testing and will only show up after long term use.
It is possible to re-weld a valve shut according to locally qualified
welding procedures provided that the connection has not been severely
damaged by steam cuts.
If the leak caused extensive damage, please contact Velan
Field Engineering Services.
When groups of valves on the same manifold begin leaking through gaskets
or through seats or show general stroking problems, it is often the
case that proper welding procedures were not followed and bolts have
loosened during the post weld heat treatment, lost anti-seize and
therefore lost bolt load.
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