Fittings: One Size Does Not Fit All

Fittings: One Size Does Not Fit All

By on December 20th, 2017 in Instrumentation

Instrumentation fittings are critical to the overall operation of your plant. When designing or maintaining your plant process lines, you need to select the right fitting for each of your applications. The fitting sizes are usually determined by the outside diameter (OD) of the tubing specified for the application. There are numerous fittings to choose from, ranging from low pressure to high pressure performance. The fitting you select will differ by the type of end connection, pressure, media and desired material. Each fitting will have advantages and disadvantages, so it is critical that you select the proper fitting for your application.

Compression fittings are designed to be used with process tubing. These fittings are normally used in applications that have pressures less than 10,000 PSI. Common materials include stainless steel, brass and steel. They are also available in some exotic materials. Compression fittings are the most commonly used connection due to its ease of use. Compression fittings are also easy to break and re-make multiple times. The cost of assembly is less expensive than the next two types of fittings.

Cone and Thread fittings
 are used with high pressure tubing that is coned and threaded. This type of fitting is used in applications that range from 10,000 PSI to 150,000 PSI. Stainless steel fittings are common due to the high pressure requirements. Since cone and thread fitting are available in various pressure ranges, you need to carefully select the fitting and tubing that matches your application. Coning and threading is a timely process, so the overall cost of installing these fittings is higher than that of a compression fitting.

Butt weld and socket weld fittings are used when you want to permanently join the fitting and tubing through a welding process. Welded fittings, when properly installed, offer a high integrity seal and better resistance to vibration. The disadvantage is the installation cost due to the equipment requirements and the cost of a certified welder. Stainless steel materials are commonly used in welded process lines.

Plastic fittings are used in low pressure (normally air) applications. These fittings are typically used with copper or plastic tubing. These fittings are easy to install and reasonably priced. One exception is the PFA or PTFE fittings which have a higher price point. These polyfluoromer fittings are recommended for acid or solvent applications because of their excellent media compatibility.

Choosing the correct fitting isn’t hard, you just need to have the right parameters and requirements for your individual application. When in doubt, call and talk to one of our experts.