Choosing Proper Connections for Copper Coils
January 15, 2009
There are different connections for copper coils, and knowing which one is appropriate for a specific application can be tricky. Connections come in myriad types, sizes and materials. In the absence of local building codes, or codes such as ASME or CRN that dictate the class and type of connection required, the following tips from Colville, Wash.-based Colmac Coil's Randy Carstens, P.E., offers a quick guide to selecting the appropriate connection.
For low flow rate and low-pressure water and steam applications, copper sweat connections are appropriate. They usually are specified as ODS, for "outside diameter sweat," and the joint is brazed to the outside diameter of the copper stub left on the connection.
ODS is common for 1.5" or smaller connections (for a 1.5" nominal size copper tube, it would be 1.625" ODS). According to Carstens, the "beauty" of the brazed joint is that it is simple, quick, generally foolproof, and, more importantly, leak-proof. Later, if the coil is removed, a portable reciprocating power saw or tubing cutter can quickly sever the tubing, allowing for coil removal.
Male pipe thread (MPT) connectors are appropriate for large-diameter connectors. The larger the connection, the more difficult brazing becomes, and brazing with a big "rosebud" tip in a confined area with flammable materials nearby can be a challenge for the installer. For connections 2.5" and larger, steel flanges often are used to simplify making and breaking the connections. Typically, Colmac Coil uses raised-face weld-neck steel flanges, where the flange has a neck in the casting for easier welding. These type of flanges also have a raised groove on the flange's face that makes gasket-sealing easier.
Carstens notes that you should choose the correct class of flange for your application's maximum operating temperature and pressure (see table). Halocarbon direct expansion coils and condensers most generally have brazed connections to avoid leaks.