The chemical plants I have worked for usually use or at least stipulate within their engineering standards, the use of "gauge valves with intergal bleeders" as the instrument process/utility connector. On all their process streams they mandate these gauge valves to have a welded end (plain male end) on the process side of the valve but allow tapped threaded connections on the instrument side. The welded end of the valve is always inserted into a sockolet type branch connector. On utility services, not steam, they mandate the same gauge valve but it can be an all threaded unit. attached to the run with a thredolet type connector. The manufacturer I am most familar with is Anderson Greenwood. We used their M5 gauge valves along with their VA bleed "needle" plug. This bleed valve is required to relieve the small amount of pressure that can built up between the gauge valve and instrument/instrument tubing. I would always suggest using a bleeder with the vent tube so the mechanic can see where its pointing before opening. Other types without the tube just have a small, not easily seen bleed hole. I know of personnel that had been injured using this type. Sorry I got long winded. In a nut shell, no threaded where allowed on environmentally or human health hazardous or flammable materials. I have seen sch. 80S nipples shear off of instrument connections, due to pulsation problems.
> What the Code says.
> parag. 328.5.3 Seal welding shall be done by a qualified welder. Seal
welds
> shall cover all exposed threads.
>
> Problem statement.
> There are quite a significant numbers of threaded nipple at the plant -
> pressure gage/vent connection, seal flush on pumps and compressors, gland
> coolers and other similar misc. applications. Many of these connections
are
> not seal welded - for obvious reason, the need to remove this piping for
> maintenance purposes.
>
> However, it also a cause of concern if the media is hazardous or if the
> service is steam. Recently, a work request was initiated by Operation to
> seal welds all threded nipple carrying steam and flammable commodity
during
> the turnaround. We see two problems - complying with the last sentence of
> 328.5.3 and maintenance during the repair of compressors/pumps or
> replacement of gages.
>
> Appreciate to hear the practice in other plants/facilities.Note that we
use
> either sch 80 or sch 160 for all trheaded nipple.
>
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Received on Tue Jun 19 20:12:00 2001
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