Screwed Connection

[cityone1]

Hi everybody
I need your response.
In my design spec. there is paragraph as bellow.
"Screwed connections are prohibited where threads provide the only seal of the pressure boundary."

I want to know why this requirement is applied.
And, this requirement shall be applied, is there any code/standard that this requirement is addressed.

Best regards,

 

[JLSeagull]

The context is necessary to really evaluate the phrase. Assuming that this pertains to piping or valves, the requirement includes flanges or welded end connections for the process connections. Threaded ends are not acceptable. The requirement would apply to the bonnet, another pressure containing connection.

 

[Ashereng]

It is common for the first valve off of the pipe to be either welded or flanged (especially in services where there is H2S present).

If you need an isolation valve, for example for a PT, the first valve may be welded or flanged, then your gauge valve, then then the PT.

Is this your contex?

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Albert Einstein
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[vpl]

I want to know why this requirement is applied.

It's applied because threaded fasteners tend not to retain the pressure boundary.

And, this requirement shall be applied, is there any code/standard that this requirement is addressed.

That depends on the type of application (service) and the country of installation.

Patricia Lougheed

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[jte]

"Screwed connections are prohibited where threads provide the only seal of the pressure boundary."

I want to know why this requirement is applied.
And, this requirement shall be applied, is there any code/standard that this requirement is addressed.

Well, to quote ASME PCC-2 2006, Article 2.3: When the convenience of a threaded connection is desired, and the reliable seal of a welded connection is required, a seal welded threaded joint is sometimes used.

Seal welding is also addressed in ASME B31.3 and probably the other B31.x codes...

jt

 

[hydtools]

Sounds like the requirement eliminates NPTF joints where thread interference is the only fluid seal. Other joints are permitted where the thread, if used, is not the pressure seal or the only pressure seal.

Ted