Common Weld Joints in Pipe Systems

When installing steel piping for water or other liquids such as gas or waste, there are a few common types of weld joints. This can vary depending on the diameter of the pipe sections, the angles, or direction shifts of the pipe. Butt joints, fillet joints, and flange joints are some of these welding applications. Read on to learn more about these joints and when to use them.

Butt Joints

Butt Joints join two pieces together, end to end. This can be done with two pieces of the same pipe or to add valves, flanges, fittings, or other equipment. If the welded materials are thicker than three-sixteenths of an inch, you use a plain or compound bevel. In larger pipes, the butt joints will need to be sealed both inside and out.

You should perform tests after completing the weld on each joint. Visually examine the welds and look for beginning and end defects, cracks, or undercuts.

Other tests done after a butt joint weld can either be a magnetic particle test (MT) or an ultrasonic test (UT). You can perform an ultrasonic test as soon as the weld has cooled. The UT test only needs to be done on one side of the joint, either inside or out.

Once the joints have passed inspection, install a protective shrink sleeve or a mortar diaper to protect the joint from corrosion if the pipes will be underground.

Fillet Joints

Fillet welding joints are common in pipeline installation. Lap, tee, and corner joints are all types of fillet joints.

• A lap joint is where two pieces of pipe overlap because the diameter of one pipe is smaller than the other.
• A tee joint creates the shape of a T when two pipes are joined or a pipe is affixed to a base plate.
• Corner joints form an L with the two pieces of metal being joined. If three branches of pipe are joined, it is called a miter joint.

Fillet joints use either a single or a double fillet. With a single fillet, the joint is sealed on the outside when the two pipes are fully seated. A double fillet seals the joint both inside and outside where the pipes meet.

Visually examine single fillet joints for completion and any faults. You should also perform an MT test. If you use a double fillet, in addition to the visual and MT tests, use an air test to 40 psi on the pocket created by the two welds. Vacuum box tests are another option on the overlapped areas.

Use shrink sleeves or mortar diapers to protect fillet joints that will be underground or exposed to the elements.

Flange Joints

Flange joints, or edge welding, occur where a valve or a manhole is installed. When installing a valve, you add a gasket in between and tighten the bolts diagonally for even torque.

You should also put a thin coat of paint down underneath the nut and washer to keep water from causing corrosion problems later. Check the bolts after twenty-four hours for continued tightness.

As with other weld joints, a visual examination should be part of the process after weld completion. Once the weld passes inspection, a shrink sleeve or corrosion protection tape can protect the weld.

Whether your pipe installation is indoors or out, large or small, let our expert welders at 3-B Welding, LLC, help you. We hire only experienced welders who can help you get your job done on time and on budget. So if you want to ensure a quality welding project, our company is the right one to call. We look forward to working with you.