SS Tubing As Per Refinery Standard

I doubt that any national standard makes a declaration relating to application specific installations.

Here is API's Recommended Practice (RP) 551
Process Measurement Instrumentation (1993)

2.2.8 PIPING
Process connections to the instruments should be furnished and installed in accordance with applicable piping and material specifications. All pipe should be deburred after cutting and blown clean of cuttings and other foreign material before assembly. As an alternative to pipe, tubing of suitable material may be used. This subject is covered in general by the project piping specification.
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I doubt that the project piping spec covers maximum length, either. It's possible that a specific refinery might have such a specification, but I know what does cover impulse tubing installation is a variety of good practice recommendations.

Published recommended practice uses terminology like:
"Keep impulse piping as short as possible and free from bends, turns, and high and low points" (avoid trapping gas in liquid or liquid in gas).

See the paper here for a thorough discussion of impulse tubing:
http://www.idc-online.com/technical_references/pdfs/instrumentation/Differential%20pressure%20meters_nel.pdf

There is no specification which can answer such a general question reliably, unless your refinery works to it's own in-house rules. Everything depends on the application.

Firstly, I assume you refer to a petroleum refinery, and the run limits you need to quantify are realistic...

Flow: measuring differential pressure across the flow element the transmitter is generally mounted below the elevation of the flow element. If both impulse lines to the transmitter are filled with a viscuous fluid that is not going to change state or density over the run length due to temperature change, there is no theoretical limit. The differential will remain constant irrespective of run-length. However, always note the transmitter manufacturer's recommendations.

Other applications, where the impulse lines require to be filled with a sealing fluid, or must be heat-traced, should be kept as short as practically possible for obvious reasons.

Pressure: Again, the properties of the process fluid defines what is practical. In this case there is a static head of liquid at the transmitter, equal to the pressure contained in the process piping, which should not decay in pressure over the run-length, unless ridiculous extremes are resorted to.

What you need to adhere to is common engineering sense. 1. Keep the length as short as other practical considerations will allow 2. where the application dictates a fall in the tubing run, ensure that the fall is constant, and 3. use as few bends and fittings as may be practical.

Hope this is of some use...