Some type of connector must be provided to attach the pipe, tube, or hose to the other components of the system and to connect sections of the line to each other. There are many different types of connectors (commonly called fittings) provided for this purpose. Some of the most common types of fittings are covered in the following paragraphs.

Threaded Joints

The threaded joints are the simplest type of pipe fittings. Threaded fittings are not widely used aboard modern ships except in low-pressure water piping systems. The pipe ends connected to the union are threaded, silver-brazed, or welded into the tail pieces (union halves); then the two ends are joined by setting up (engaging and tightening up on) the union ring. The male and female connecting ends of the tail pieces are carefully ground to make a tight metal-to-metal fit with each other. Welding or silver-brazing the ends to the tail pieces prevents contact of the carried fluid or gas with the union threading.

Bolted Flange Joints

Bolted flange joints (fig 9-53) are suitable for all pressures now in use. The flanges are attached

Figure 9-53.-Four types of bolted flange piping joints.

Figure 9-54.-Various types of welded joints.

to the piping by welding, brazing, screw threads (for some low-pressure piping), or rolling and bending into recesses. Those shown figure 9-53 are the most common types of flange joints used. Flange joints are manufactured for all standard fitting shapes, such as the tee, cross, elbow, and return bend. The Van Stone and the welded-neck flange joints are used extensively where piping is subjected to high pressures and heavy expansion strains. The design of the Van Stone flange makes it easier to line up the fastening holes in the two parts of the flange.

Welded Joints

The majority of joints found in subassemblies of piping systems are welded joints, especially in high-pressure piping. The welding is done according to standard specifications, which define the material and techniques. Three general classes of welded joints are fillet-weld, butt-weld, and socket-weld (fig 9-54).

Silver-Brazed Joints

Silver-brazed joints fig. 9-55 are commonly used for joining nonferrous piping when the pressure and temperature in the lines make their use practicable-temperatures must not exceed 425F; for cold lines, pressure must not exceed 3000 psi. The alloy is melted by heating the joint with an oxyacetylene torch. This causes the molten metal to fill the few thousandths of an inch annular space between the pipe and the fitting.

Unions

The union fittings are provided in piping systems to allow the piping to be taken down for

Figure 9-55.-Silver-brazed joints.

Figure 9-56.-Unions/threaded pipe connectors.

repairs and alterations. Unions are available in many different materials and designs to withstand a wide range of pressures and temperatures.  Figure 9-56 shows some commonly used types of unions/threaded pipe connectors. The union is most commonly used for joining piping up to 2 inches in size.

Flared Fittings

Flared fittings are commonly used in tubing lines. These fittings provide safe, strong, dependable connections without the necessity of threading, welding, or soldering the tubing. Flared fittings are made of steel, aluminum alloy, or bronze. Do not mix materials when using these fittings. For example, for steel tubing use only steel fittings and for copper or brass tubing use only bronze fittings, figure 9-57 shows the most common types of flared fittings.

Flareless Fittings

Flareless fittings (figs. 9-58 and 9-59) are suitable for use in hydraulic service and air

Figure 9-57.-Flared-tube fittings.

Figure 9-59.-typical flareless fitting.

service systems at a maximum operating pressure of 3000 psi and a maximum operating temperature of 250F. Flareless fittings are installed to conserve space and to reduce weight, installation time, and system cleaning time. Do not use flareless fittings if you do not have enough space to properly tighten the nuts or if you have to remove the equipment or piping for access to the fittings. An exception to this rule is a gauge board. It is designed so it may be removed as a unit for repairs or alterations. Do not use flareless fittings where you cannot easily deflect the piping to permit assembly and disassembly.

Before assembly, ensure the tubing end is square, concentric, and free of burrs. For an effective fitting, be sure the cutting edge of the sleeve or ferrule bites into the periphery of the tube; you can do this by presetting the ferrule.