The following variables should be considered when ordering tubing for use with fittings: surface finish, material, hardness and wall thickness.
Instrumentation tubing selection
First of all it is essential to have a proper selection of instrumentation tubing, as well as proper handling and installation. It must also be combined with an appropriate selection of FITOK fittings in order to achieve reliable tubing systems.
The following variables should also be considered when ordering tubing for use with fittings:
– Surface finish
– Material
– Hardness
– Wall thickness
Instrumentation tubing surface finish
Many ASTM specifications cover the above requirements, but are often not very detailed about surface finish. For example:
ASTM A450, a general pipe specification, states:
12. Straightness and finish
12.1 Finished tubes shall be reasonably straight and shall have smooth, burr-free ends. They shall have a workmanlike finish.
Surface imperfections (Note) may be removed by grinding. Provided that a smooth, curved surface is maintained, and the wall thickness is not reduced to a value less than that permitted by this specification or by the product specification. The outside diameter at the point of grinding may be reduced by the amount removed.
Note: An imperfection is any discontinuity or irregularity found in the tube.
Material
With respect to ordering, our instructions for each type of tubing are shown in the respective tables.
Hardness
The key to selecting the proper tubing for use with FITOK metal fittings: The tubing should be softer than the fitting material. The fittings are designed to work properly with the tubing that is suggested in the ordering instructions.
Wall thickness
The tables show the working pressure of the pipes over a wide range of wall thicknesses. In addition, the allowable pressure ratios are calculated from the S values specified in ASME B31.3. With regard to process piping. FITOK fittings have been repeatedly tested to the minimum and maximum wall thicknesses indicated. FITOK fittings are not recommended for pipe walls outside the ranges indicated in the tables for each size.
Handling of instrumentation tubing
It is important to handle tubing correctly to reduce scratches and protect the surface finish.
In fact tubing should never be dragged out of a tubing frame or across a rough surface.
Pipe cutters or hacksaw blades should be sharp. Do not make deep cuts with each turn of the cutter or with each stroke of the saw.
The tubing will pass through the ferrules without damaging the sealing edge of the ferrule.