SS Tubes for Instruments

How big is the instrument ?

I meant instruments like Differential pressure transmitters , Pressure transmitters , or any instrument that needs an impulse line to be connected to the process .

Got it. CR4 has a section on instrumentation. Admin don't generally like posts being made twice, but I think they would be OK with you repeating the question over there. With it being the weekend, you may not get much feedback until next week.

I think we are in instrumentation forum now , by the way , thanks for your interest .

lol - I never much look at thread location .

SANDVIK make the stuff, so I guess if you approach them with the requirement they can help sort the right size of tubing. There seems to be a lot of sites that may be of help.

In my petrochemical experience, it is based on a standard convention, based on non-plugging, mechanical strength (so it is not easily broken), and ease of installation. We always used 3/8" OD - speaking here about impulse lines with no normal flow. If the line is flowing - to a sampler or analyzer, for example - each would have to be sized to account for lag time, pressure drop, etc.

Thx , I will consider your recommendations upon installation.

I doesn't matter much for pressure transducers. There is no flow taking place in the tube. Volume of fluid isn't critical.

The inside diameter of the tube is important only because a larger diameter of fluid will exert a higher hydraulic pressure on the sensor of the device than a small diameter tube. That's something that can be noted during calibration.

It will matter with flow meters. Many of them are plumbed directly into the piping.

Thx , I will take your note into consideration and keep checking during calibration .

The pressure to be handled will govern the tube thickness in relation to its diameter.

The fluid will determine what corrosion resistance the tubing must have.

There is flow in the tubing, even if only for brief intervals. Response time of instruments may depend on this; hence your question is valuable. A search on "instrument tube sizing" or some manufacturers' literature may help.

CR4 users Tony Kuphaldt and Iris, et.al., are well informed on these topics; perhaps they will see this thread and offer comments.

Tube sizing may change as a function of length of tube run more so than just flow.

Consulting installation literature for the specific gauge should answer OP's question.

Thank you for the valuable documents , I downloaded the best practice file but for the other one which is uploaded to scribd I couldn't do this , do u have another link for this ?

Try searching for the document name on Scribd. That same document has been uploaded several times. Be aware the Scribd is now an exchange site, you upload one, you get to download one. So make an account, upload a document and download the one you need.

Here's a vendor document with pressure ratings at various diameters and wall thicknesses. It also has an example of de-rating the tubing pressure limit at elevated temperature (page 3):

http://www.swagelok.com/downloads/webcatalogs/EN/MS-01-181.PDF

There is one "standard" I'm aware of:

ASME MFC-8M-2001 Fluid Flow in Closed Conduits: Connections for Pressure Signal Transmission between Primary and Secondary Devices,

but I find the other sources adequate.

Thank you so much

Instrumentation in what application: industrial, medical? Are we talking about large bore SS tubes or miniature ones?

the application is industrial , and here I am talking about impulse lines , 1/2" , 3/8 " , 1" , thx

The criteria are the obvious: instrument port size and max operating pressure.

Unfortunately, you have given relevant information to work with

The tubing is generally available in two wall thicknesses, where the thicker one is obviously for higher pressure application (it is also more difficult to bend,so if you aren't particularly strong, or used to physical effort, please do consider the thinner wall tube..on the other hand, you have not mentioned the length of the tubing run/s, and whether or not the tubing is connected directly to the process, or perhaps only between the instrumentation).

Whoever supplied your instruments should have all the info necessary to advise on the tube wall thickness, as pertinent to your specific application.