ASME B 16.5 - Table 8 - Blind Flange with Threaded Connection.

[Chandra2021]

We have a situation where a 3/4" NPS Flange with a threaded hole is connecting A 3/4" valve to an Instrument tubing. The tubing is 1/2" NPS Size.

One way to connect this Flange to Tubing is to use 3/4" to 1/2" Adapter. Another suggested solution is to bore 1/2" NPS Tapping / Thread in the Blind Flange.

As per one opinion, we can have only 3/4" NPS threaded Hole on 3/4" NPS Blind Flange as per Column 1 of Table 8 (ASME B16.5). If we provide 1/2" Thread on this Blind then this will not ASME flange anymore. If the 1/2" tapping is required, we need to carry out the necessary calculation to prove, it has the necessary strength at required fluid pressure. And obviously, this will be a non-standard ( Special) piping component.

Counterview to above: Table 8 in 16.5 does not talk about (It's silent) the size of the threaded connection on threaded Blind. Hence, we can tap a 1/2" NPS thread in this Flange.

My intent is not to make this a special item but to use Standard ASME Pipe Fitting. Please provide your interpretation of Table 8 on this issue.

 

[LittleInch]

Table 8 is for flanges and their connections for class 150 flanges. or at least that's the latest version I've got (2017)
So you could use a screw on flange onto a 3/4" tapped nipple, pipe or solid reducer.

It does not talk about drilling or tapping holes in blind flanges.

That is table 6, where the smallest size shown is 1", so your 3/4" flange doesn't have an allowable size for drilling a hole in blind flange.

Is this existing or future or why are you asking?

I think stick to a 3/4" connection into your 3/4" screwed flange and leave it at that.

why complicate things?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XL83NL]

Making a reducing flange, by using an NPS 3/4" high hub as a rough starting geometry, and applying a 1/2" threaded connection, is completely in line and compliant with B16.5.
It will however be more expensive than using a 3/4" NPS flange with 3/4" threaded hole, and using a male NPT connector to go to tubing. We do this all day in our plants, and it works very good.

Huub
- You never get what you expect, you only get what you inspect.

 

[SnTMan]

Similar discussion: thread794-482506

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[LittleInch]

I find any instrument main connection less than 1" or preferably 2" to be rather weedy looking and has the potential for mechanical damage.

The same points were made in that earlier thread.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TBP]

Why not just buy a 3/4" X 1/2" reducing flange?

Quick internet search:

https://shop.dnow.com/product/775320-3-4-in-threaded-reducing-flange