Learn the Techniques for High Quality Nipple Welding

An Introduction to Nipple Welding

Nipple welding refers to the process of joining tubular pieces of metal together by welding. It gets its name from the shape of the tubing, which often resembles a nipple. Nipple welding is commonly used in automotive, aerospace, and industrial fabrication applications wherever pipes, tubes, or nipples need to be connected.

Why Nipple Welding is Used

Nipple welding provides a strong, leak-proof connection between tubular components. Some key benefits of nipple welding include:

• Ability to join dissimilar metals
• Minimal joint preparation needed
• Suitable for joints with tight fit-up tolerances
• High quality, repeatable welds
• Relatively simple process compared to other pipe/tube joining methods

For these reasons, industries like automotive exhaust fabrication often rely on nipple welding to connect exhaust pipes and components. The aerospace industry also uses nipple welding to join hydraulic lines, fuel lines, and other tubing systems in aircraft.

Common Nipple Welding Techniques

Several techniques can be used for welding nipples and tubular structures. The most popular include:

TIG Welding

TIG (Tungsten Inert Gas) welding uses a non-consumable tungsten electrode and inert shielding gas to produce high quality welds in thin materials. For nipple welding, TIG allows precise control over heat input, which helps avoid burn-through and warping in small tubing. TIG can weld most metals including stainless steel and aluminum.

MIG Welding

MIG (Metal Inert Gas) welding uses a continuously fed consumable wire electrode and inert shielding gas. MIG welding offers high deposition rates, making it faster than TIG welding for many applications. MIG can also weld a wide range of metals with good penetration and quality. Disadvantages are lower precision vs TIG welding and more spatter.

Stick Welding

Stick welding uses a manual consumable electrode covered in flux to provide shielding. Though not as widely used for nipple welding, stick welding allows welding of dirty or rusty metals thanks to its flux shielding. Stick welding can be done in all positions but is slower than MIG or TIG welding for tubular joints.

Laser Welding

Laser welding focuses a high power laser beam on the joint area to melt and fuse the metals. Laser welding is extremely precise with low heat input, making it suitable for welding thin-walled tubing and small diameter nipples. It provides deep weld penetration and very fast welding speeds. The equipment is complex and expensive, limiting its use.

Friction Welding

Friction welding rubs two parts together under pressure at high speeds, generating heat through friction to fuse the metals. The process only takes seconds and can join dissimilar tube materials. Due to the high forces and rotational speeds, friction welding requires specialized machinery capable of holding round tubular parts.

How to Prepare for Nipple Welding

Proper preparation is key to achieving high quality nipple welds. Here are some tips on preparing for a nipple welding project:

Select the Right Process

Choose a welding process suitable for the base metal, joint design, tube size, equipment availability and production rate. TIG, MIG, and laser welding are common choices for most nipple welding applications.

Clean the Materials

Thoroughly clean the tubing in the weld area using solvents like acetone. Remove any dirt, oil, corrosion, mill scale, or coatings that could contaminate the weld and cause defects.

Secure the Tubes

Fixture the tubes securely to prevent any movement during welding. Misalignment can lead to a failed weld. Clamps, vices, jigs, and tack welds help achieve accurate fit-up.

Bevel Edges

For butt joints, beveling the tube ends ensures full penetration welds. Common bevel angles range from 20-40°. Match the bevel to the welding process and base metal thickness.

Use Backing Strips

Backing strips made from ceramic or copper help control the weld shape profile and prevent burn-through on thin tubing. Make sure the gap between tubes allows for full penetration of the weld metal.

Nipple Welding Technique

With tight fit-up and attention to technique, high quality nipple welds are achievable. Here are some technique tips for a sound weld:

Maintain Arc Length

Hold a consistent arc length based on the welding process. For MIG and stick welding, this is roughly the width of the electrode. For TIG welding, a tighter 1/8” arc gap is ideal.

Use Proper Torch Angle

For small diameter tubing, aim for a 45 degree lead angle to ensure the arc reaches the bottom of the joint. Larger tube welding may use angles down to 15 degrees.

Weld Both Sides

To fill the joint and prevent burn-through, make sure to weld both sides of the nipple seam to deposit weld metal evenly.

Use Stringer Beads

Stringer beads or continuous beads without weaving result in the best penetration for nipple welds. Whip and pause at the weld toes to improve fusion.

Watch Your Speed

Move steadily but not too fast to avoid lack of fusion or undercut weld defects. Typical weld speeds are around 4-8 inches per minute.

Overfill Slightly

Build up weld reinforcement slightly above the surface to compensate for stacking bead concavity and prevent craters.

Nipple Welding Defects

Flaws in nipple welds stem from issues like poor preparation, technique, or welding parameters. Here are some common nipple welding defects:

Lack of Fusion

Incomplete bonding between weld and base metal occurs when the joint doesn't melt properly. Causes include too fast welding speed, improper torch angle, or dirty base material.

Porosity

Gas bubbles trapped in the solidifying weld metal. Moisture contamination, unstable arc, or improper shielding gas levels can cause porosity.

Undercut

Grooves melted into the base metal adjacent to the weld toe due to excessive heat input or fast travel speed.

Burn Through

Complete penetration through the tube wall due to poor technique or excessive heat input.

Cracking

Cracks in the weld or heat affected zone caused by issues like improper joint design, contamination, or mixed base metals.

Safety Precautions

Nipple welding comes with certain hazards welders should protect themselves against, including:

Electric Shock

Contact with live electrical parts can injure or kill. Wear insulating gloves and only weld in dry conditions.

Fumes

Welding produces dangerous metallic fumes. Use proper ventilation or local exhaust at the arc.

UV Radiation

The welding arc emits powerful ultraviolet light that can burn skin and eyes. Wear safety glasses/goggles and cover exposed skin.

Fire Hazard

Sparks, spatter, and heat from welding can ignite flammable materials. Clear away combustible objects before welding.

With responsible safety practices, nipple welding can be done productively and safely. Mastering the specialized techniques for tube welding also takes time and practice. Take a hands-on welding training course to learn how to produce professional quality nipple welds.

FAQs

What are some common materials that are nipple welded?

Carbon steel, stainless steel, aluminum, nickel alloys, titanium, and copper are frequently nipple welded. The material chosen depends on factors like strength, corrosion resistance, temperature resistance, and cost.

What size tubing can be nipple welded?

Nipple welding can join tubing from less than 1 inch up to several inches in diameter. Very small hypodermic needle tubing down to 0.5mm can also be welded.

Is nipple welding only used for round tubing?

While most nipple welds are done on round tubing, pipes, and fittings, it's also possible to weld square, rectangular or other shaped hollow sections. The joint preparation and technique may differ compared to round nipples.

Can I nipple weld with a hobby welder?

Small portable welders can be used, but high amperage is needed to achieve full penetration welds on thicker materials. Use a welder of at least 180 amps capability for nipple welding up to 1/4 inch wall steel tubing.

Is nipple welding hard to learn?

A moderate level of welding skill is required. Mastering proper torch position, speed, and heat input for quality tube welds takes practice. Taking a tube welding course helps develop expertise faster.