Weld fittings (also called "welding fittings") are attached by welding. In most cases weld fittings are not fabricated by welding. Instead, they are usually formed by cutting short pieces from pipe, so it would be incorrect to call them "welded" fittings.

Since they first became available in the United States around 1930, weld fittings have continuously gained acceptance as the most effective and economical pipe joining method for many industrial applications. In many industries welded piping systems have replaced their predecessors -- the threaded and/or flanged designs. This is an updated version of the product training course introduced by Supply House Times in 1979, authored by Don Arnold.

Made In Many Materials

Weld fittings are butt-welded to the pipe or flange, which is why they are also commonly referred to as "butt weld" fittings. They are made in carbon steel, alloy steel, stainless steel, aluminum and exotic alloys for high temperature and highly corrosive applications. Weld fittings are generally wrought

(made from pipe, rather than by forging or plate). While carbon steel weld fittings are primarily made from seamless pipe, stainless steel weld fittings are made from both welded pipe and seamless pipe.

Most standard wall and thinner stainless weld fittings are made from welded pipe; heavier wall stainless fittings are usually made from seamless pipe.

Permanently Leak-Proof

Weld fittings gained wide acceptance by the majority of designers, engineers and end users because of the many advantages of all-welded piping systems. The biggest advantage is being permanently leak-proof, thus requiring little or no maintenance for the life of the system.

In cases of thermal applications requiring insulation, the permanent welded joint precludes the need of removing insulation for maintenance, servicing leaking gaskets or tightening bolts. The leak-proof welded joint insures greater safety for the workers and the surrounding environment, particularly where the lines are subject to high internal pressure.

Strongest Piping

The great strength of welded joints is another factor in their selection. Welded joints are as strong or sometimes even stronger than the pipe itself, providing years of dependable, maintenance-free service. The pressure rating of a flanged connection (using the same wall pipe) is downgraded to the sealing capability of the gasket. Similarly, the pressure rating of a threaded connection (using the same wall pipe) is downgraded to the sealing capability of the threaded fitting.

Fits In Any Space

Weld fittings also have a unique flexibility that lend themselves to be close nested. This allows piping designers to tailor the systems to work in a limited space, to conform to the physical parameters of the building, terrain, or the position of equipment.

The weld joints are virtually flush with the pipe, which allows lines to be placed directly against walls, ceilings, equipment or other lines. True circularity and uniform wall thickness of weld elbows allow for them to be cut at odd angles and still align perfectly with the pipe.

Easy To Hang

Weld fittings are light in weight (a welded elbow connection weighs approximately one-fourth as much as a flanged connection). This can save tons of metal in a piping installation, along with greatly reduced labor by eliminating hanging costs.

Less Turbulence

In addition to the advantages already cited, the clean, smooth contour of welded joints eliminates pockets and crevices that impede flow. Threaded joints have many sharp corners that cause much greater frictional resistance, turbulence, pressure loss, erosion, corrosion and debris accumulation. Most fabricated sectional pipe bends cause twice as much frictional resistance to the flow in contrast to the smooth flow of a long radius welded elbow.

Lower Material Cost

Especially in stainless piping, weld fittings result in dramatic savings in material cost for both fittings and pipe due to the fact that a welded joint does not require extra wall thickness for threading. Since the majority of process piping is operated at low pressures (less than 150 PSI), welded pipe and fittings can take advantage of the high strength of welded piping while at the same time enabling lower cost standard wall (or thinner) pipe to be used rather than more expensive heavier wall pipe and fittings.

Prefabrication

Welded piping systems lend themselves especially well to prefabrication under ideal working conditions in a fab shop, thereby saving substantial field labor. Then the components can be assembled and erected in the field into a single unit with a few simple tie-in welds by qualified welders.

Summary

By virtually any comparison, welded piping systems are superior to other joining methods. Welded piping is safer, stronger and more dependable, regardless of how severe the conditions may be. This superiority directly or indirectly enhances many phases of industrial operations, from design, management, budgeting and plant operation. Weld fittings help reduce production delays or shutdowns for unscheduled maintenance.