Standards re: instrument tubing
Standards re: instrument tubing
(OP)
I'm doing a literature search to find out what standards may provide specific direction on minimum sizes for instrument tubing. The closest I've come is in PIP. Our internal standards lay out these minimums, but I'm having a tough time locating the acknowledged source for these requirements. Does anyone know where I can find a standard that speaks to minimum instrument tubing sizes for impulse, supply, and signal lines?





RE: Standards re: instrument tubing
www.flowprogramme.co.uk
2) ISA-77.70-1994 (R2005) Fossil Fuel Power Plant Instrument Piping Installation
The design of instrument sensing and sampling lines in a power plant is covered by ANSI B31.1,
"Power Piping," latest version with addenda.
4.1.1 Process tap connections
All of the material between the root valve(s), including the root valve(s) and process connection,
shall be the same material as the process pipe or vessel or shall be a material compatible with
the process fluid, pressure, temperature, and connection methods. The connection shall be a
minimum of ½ inch (12.7 mm) nominal pipe size for service conditions when pressures are 900
psig (6.21 MPa) or less, and temperatures are 800°F (426.67×C) or less. The minimum size shall
be ¾ inch (19.05 mm) for conditions that exceed either of those limits.
RE: Standards re: instrument tubing
RE: Standards re: instrument tubing
I think the line size is determined more by mechanical strenght than anything. 3/8 or 1/2" is self supporting to a degree wheras 1/4" needs lots od support.
My 2c worth
Roy
RE: Standards re: instrument tubing
Length
In addition to impulse lines, instrument tubing includes sample transport tubing. Although 90 m is a long run it is not uncommon.
Diameter
The most common impulse lines include 1/2-inch OD; and 3/8-inch OD tubing is sometimes used for impulse lines in natural gas plants. Properties such as high pressure or high viscosity affect the tubing selection.
Analyzers often use 1/16-inch OD tubing (within the oven of a GC for example).
Material
Copper was commonly for air supplies and even steam tracing fourty years ago. Copper is rarely permitted by most clients in the hydrocarbon business today.
For process, the piping material is regarded as the "minimum" material. In my experience, type 316 stainless steel has been the most commonly used tubing for instrumentation in a carbon steel line specification. However recent trends to higher alloys are becoming common. This appears to be in response to low grade tubing in the market place. I don't know the origin of the problematic tubing. Some consider type 317 even for air due to poor performance of type 316 in offshore environment. At least one major operating company is actually using alloy 625 or 825 for impulse lines in lieu of type 316 stainless steel. These nickel alloys are very expensive.
RE: Standards re: instrument tubing
Roy