How To Weld Magnetized Pipe: A Step-By-Step Guide To Stop Arc Blow

You are trying to weld a pipe, but the arc keeps jumping around. It sputters and wanders off course. This is frustrating and wastes your time and materials. You might be dealing with a magnetized pipe. This problem is called arc blow. It happens when magnetic fields in the pipe disrupt your welding arc.

This guide will show you how to fix it. The best way is to demagnetize the pipe before you weld. We will cover simple steps to do this. You will learn why it happens and how to prevent it. This guide is for welders of all skill levels. It uses easy words and clear instructions.

The Quick Solution: How to Neutralize Pipe Magnetism for Welding

If you need a fast fix, follow this method. It uses your welding machine to remove the magnetism. This is the most effective way to solve the problem.

First, you need a few tools. Get a welding machine that can use AC current. You also need the ground clamp and cable from your welder. A simple compass is important too. The compass helps you find the magnetic poles on the pipe.

Here is the step-by-step process. It will neutralize the magnetic field in the pipe.

Step one is to find the magnetic poles. Use the compass and hold it near the pipe. Watch where the needle points. The end of the needle that points to the pipe is attracted to the pipe’s south pole. Mark this spot on the pipe. You need to know where the north and south poles are.

Step two is to set up the ground cable. Wrap the ground cable from your welder around the pipe. Make several loops. Five to ten loops are usually good. Place the loops near the area you plan to weld. This setup creates a magnetic field that can cancel out the pipe’s magnetism.

Step three is to use AC current. Set your welding machine to AC mode. Do not use DC mode. AC current changes direction many times per second. This helps to break up the magnetic field. Attach a small scrap piece of metal to the pipe. Strike an arc on this scrap piece. Hold the arc for a few seconds. Then, slowly move the arc away from the pipe. This action draws the magnetism out.

Step four is to check your work. Use the compass again to test the pipe. The needle should not be pulled strongly toward the pipe anymore. If it is, repeat the process. Sometimes, it takes a few tries to fully demagnetize the pipe.

This method works well for most situations. It uses tools you likely already have. Now, you can weld without the arc blowing around.

Understanding the Problem: What Is Arc Blow?

Arc blow is a common issue in welding. It happens when the welding arc does not stay where you want it. The arc moves erratically. This makes it hard to create a good weld. The main cause is magnetism in the metal you are welding.

Think of it like trying to write with a pen while someone shakes your hand. You cannot draw a straight line. In welding, the magnetic field acts like that shaking hand. It pushes and pulls the arc away from your target.

This problem is more common with ferrous metals. Ferrous metals contain iron. Iron can hold a magnetic charge. Pipes are often made of steel, which is ferrous. Over time, pipes can become magnetized.

Common Causes of Magnetized Pipe

Pipes can become magnetized for several reasons. Knowing the causes can help you prevent the problem in the future.

One cause is induction. If a pipe is near electrical equipment or power lines, it can pick up a magnetic charge. This happens because electricity creates magnetic fields. The pipe acts like a magnet after being exposed.

Another cause is previous inspections. In industries like oil and gas, pipes are often checked with magnetic particle inspection. This test uses magnetism to find cracks. After the test, the pipe might stay magnetized.

Handling with magnets can also cause it. Sometimes, magnets are used to hold pipes in place during fabrication. This can leave the pipe magnetized.

The Earth itself has a magnetic field. Over long periods, especially with large pipelines, the Earth’s field can slowly magnetize the metal. This is less common but possible.

Understanding these causes helps you identify why your pipe is magnetized. It also shows that this is a normal issue. You are not alone in facing it.

3 Proven Methods to Demagnetize Pipe Before Welding

Demagnetizing the pipe is the best way to ensure a good weld. Here are three methods you can use. They range from professional techniques to simple field fixes.

Method 1: The AC Weld Technique

This is the most effective method. It uses your welding machine to remove the magnetism. Follow these steps carefully.

Gather your tools. You need a welding machine with AC capability. You also need the ground clamp and cable. A compass is essential for finding the magnetic poles.

Locate the magnetic poles. Use the compass as described earlier. Mark the north and south poles on the pipe. This tells you where the magnetism is strongest.

Set up the AC field. Wrap the ground cable around the pipe. Make sure the wraps are tight and close together. The number of wraps affects the strength. More wraps create a stronger counter field.

Apply heat and draw out the field. Set your welder to AC mode. Use a low amperage setting. Strike an arc on a scrap piece attached to the pipe. Hold the arc for five to ten seconds. Then, slowly move the arc away from the pipe. This pulls the magnetic field out with the heat.

Verify and repeat. Check the pipe with the compass. If the needle still moves toward the pipe, repeat the process. You might need to do this a few times. Be patient, as it can take several attempts.

This method works because AC current reverses direction. It constantly changes the magnetic field in the pipe. This breaks up the existing magnetism. It is a reliable way to demagnetize most pipes.

Method 2: Using a Portable Demagnetizer

If you work in a professional shop, you might have access to a portable demagnetizer. This is a specialized tool designed for this purpose.

A demagnetizer is a device that generates a strong alternating magnetic field. You pass the pipe through this field. The field neutralizes the pipe’s magnetism.

To use it, first, turn on the demagnetizer. Then, slowly move the pipe through the opening in the device. Make sure the entire length of the weld area passes through. You might need to do this several times.

Afterward, test the pipe with a compass. The magnetism should be gone. This method is fast and efficient. But it requires buying or having access to the tool. It is best for high-volume work.

Method 3: The Heat-and-Cool Method

This is a last-resort method. It is less reliable but can work in some cases. Use it only if you have no other options.

Heat the pipe with a torch. Use an oxy-acetylene torch or similar. Heat the area around the weld to a specific temperature. You want to heat it to below critical temperature. For steel, this is about 700 degrees Celsius. Do not overheat, as it can warp the pipe.

Let the pipe cool slowly. Do not quench it with water. Allow it to air cool. The slow cooling can reduce magnetism by relaxing the metal’s structure.

After cooling, test with a compass. If the magnetism is reduced, you can try welding. But this method is not guaranteed. It might not work for strongly magnetized pipes. Also, it can damage thin pipes by warping them.

Use this method with caution. It is better to use the AC weld technique if possible.

Advanced Tips for Specific Scenarios

Sometimes, general methods need adjustments. Here are tips for special cases.

Tacking and Welding Small Diameter Pipe

Small pipes can be tricky. They often have stronger magnetic fields relative to their size. This makes demagnetization harder.

Use a lower amperage on your welder. High heat can make the problem worse. Also, weld faster. A quicker travel speed reduces the time the arc is exposed to magnetism.

Choose the right welding rod. Cellulose rods like 6010 or 6011 work better. They can handle a less stable arc. Low-hydrogen rods like 7018 might not work as well. They require a steadier arc.

When tacking, place tacks in different positions. This can help balance the magnetic fields. Experiment with ground clamp placement too.

Managing Residual Magnetism in Large Structures

Large pipes or structures might not demagnetize fully. You might have to weld with some residual magnetism.

Move your ground clamp to different points. Try placing it on different sides of the weld joint. Find a spot where the arc blow is minimal. This is often called finding the sweet spot.

Use multiple ground clamps if possible. Place them around the weld area. This can help cancel out the magnetic fields.

Weld in short sections. Instead of a continuous bead, weld a little at a time. This reduces the effect of arc blow over long distances.

These tips help you adapt to challenging situations. They show that even with some magnetism, you can still achieve a good weld.

Avoiding Costly Errors: What Not to Do

Mistakes can make the problem worse. Here are common errors to avoid.

Do not use DC current for demagnetization. DC current will magnetize the pipe more. It strengthens the existing field. Always use AC current for this process.

Do not place the ground clamp incorrectly. If the clamp is on the wrong side, it can increase arc blow. Place it close to the weld area. Experiment with different positions.

Do not give up too soon. Demagnetization might require several attempts. Be patient and repeat the steps until the pipe is neutral.

Avoid using the wrong rods. Some rods are not suited for magnetized pipes. Stick to recommendations like 6010 for better results.

Troubleshooting: My Weld is Still Sputtering

If you still have problems, check these things. This list helps you diagnose the issue.

First, verify your welder is on AC mode. It is easy to forget to switch from DC.

Second, check the cable wraps. Did you wrap enough loops? More loops might be needed for stronger magnetism.

Third, confirm you found the correct poles. Use the compass properly. If the poles are wrong, the demagnetization might not work.

Fourth, inspect your equipment. Make sure the ground clamp connection is clean and tight. A poor connection can cause issues.

Fifth, consider the pipe condition. Rust or scale on the pipe can interfere. Clean the area before welding.

By checking these points, you can often find the solution. Do not hesitate to start over if needed.

Frequently Asked Questions About Welding Magnetized Pipe

Here are answers to common questions. They provide quick help and reinforce key points.

Can you weld magnetized pipe without demagnetizing it?

Yes, it is possible, but not recommended. Welding without demagnetizing leads to poor weld quality. The arc may not penetrate properly. This can cause weak welds or defects. It is better to demagnetize first for a strong, safe weld.

What is the best rod for welding magnetized pipe?

The best rods are often cellulose types like 6010 or 6011. These rods have a digging arc that can cut through minor magnetism. They are more forgiving than low-hydrogen rods like 7018. Always match the rod to your specific welding process and material.

Why is my new pipe magnetized?

New pipes can be magnetized from manufacturing or handling. They might have been near magnetic equipment during transport. Or, they could have been stored in a way that exposed them to magnetic fields. It is a common issue, so always check before welding.

What tools do I need to demagnetize pipe?

The basic tools are an AC welder, ground cable, and a compass. For professional work, a portable demagnetizer is useful. Always have safety gear like gloves and a helmet. These tools are simple and effective for most jobs.

Welding magnetized pipe is a challenge, but it is solvable. By following these steps, you can stop arc blow and create strong welds. Remember to demagnetize first, use the right tools, and avoid common mistakes. With practice, you will handle magnetized pipes with confidence. Happy welding!