In pipeline construction, proper weld preparation and interpass cleaning is crucial to the success of the overall process. Weld failure in these applications can be disastrous, so every weld must meet stringent quality requirements. If weld defects are found, the necessary repairs add time and money to a process that already has a tight project timeline and is most likely occurring in a challenging environment.
Therefore, following best practices for weld prep beforehand is key. Ensuring proper penetration between weld passes also helps operators minimize defects and produce the high-quality welds necessary in these demanding applications.
Product choice
Knowing what abrasive product to use for the job is an important first step in getting good results. From flap discs and grinding wheels to wire brushes, a range of abrasive products are available for pipeline weld prep and interpass cleaning. Choosing the right one helps promote high weld quality while also saving time, increasing overall efficiency. Here are some common options and their recommended uses for consideration.
Wire brushes and wheels: Power wire brushes and wheels are good choices for removing light surface rust or loose material on the pipe surface without affecting the base material. They can be used to clean the surface prior to welding and are also useful for interpass cleaning. Brush options include stringer bead wheels and wire cup brushes (good for large-diameter pipe and faster cleaning). The difference between a wire wheel and wire cup brush comes down to surface coverage. For targeted cleaning, a wheel is best. In pipeline prep, this would be cleaning welds to get down into the channel of a pipe. Because wire cups cover a larger area, they are better at cleaning large surfaces.
Flap discs: When the pipe has more than light surface rust and defects, such as pits in the metal, a more aggressive solution is likely needed. That’s because the bevel should always be completely cleaned, including the removal of any rust or pits. Flap discs can efficiently grind rust, pits and imperfections while reducing the gouging risk that comes with a grinding wheel. Available in various material types and grit sizes, flap discs provide the necessary aggression and material removal. For example, a flap disc with an aluminum backing is more rigid with less flex, allowing operators to maintain the edge of the bevel without rounding it, which impedes properly filling the weld.
Grinding wheels: Grinding wheels are a good choice for grinding the root pass, facing the land – an important step in butt welding – and transitioning. With grinding wheels, operators must take care to avoid gouging the base material by using too much pressure. A wheel that is balanced reduces chatter and provides more control. Weiler Abrasives’ Tiger pipeline grinding wheels are designed specifically for pipeline notching and grinding and are optimized to break down and grind hot welds, which eliminates glazing.
Prep and cleaning tips
Readying a piece of pipe for welding generally begins with preparing the bevel. Often, the pipe being delivered to the jobsite already has a bevel created, but it still requires cleaning and shoring up the land using a grinding wheel. The land is a flat area that allows for proper spacing between the pipe ends so they can be aligned and tacked together for welding. A notching wheel or 1/4-in. grinding wheel both work well for this task. The operator should avoid dwelling too long in one spot with the grinding wheel, though, to avoid gouging. It’s also recommended to keep the wheel in motion and as flat as possible when in use.
After the bevel and land have been prepared, the pipe opening is cleaned to get it ready for welding. Wire wheels are commonly used for this task, but if the pipe has a lot of heavy rust, a more aggressive product may be needed. The condition of the base material can vary a lot when it arrives on a jobsite, and the condition plays a role in choosing the right abrasive product for cleaning. A pipe with only light surface rust requires a different conditioning product than one with heavier rust.
Next up is interpass cleaning, which requires a different set of abrasive products. The first pass, called the root pass or bead pass, is the most critical because it creates the foundation for the remaining passes to be added on top of the initial weld bead. Once the root pass is laid, the operator must grind the weld to ensure proper penetration for the next pass, called the hot pass, to ensure full penetration. Using a 1/8-in. grinding wheel for this task helps create a flat or U-shape in the bottom of the weld. The hot pass must be completed quickly after the root pass to avoid the pipe temperature falling below allowable levels.
The number of subsequent filler passes necessary depends on pipe diameter and wall thickness, but each pass will require cleaning, typically with a knot wire brush known as a stringer bead wheel. This product removes inclusions or impurities that rise to the surface of the weld without removing base material. In particular, a wire wheel with a narrow face works well for this. If the application involves large-diameter pipe, the filler passes may have a wider V-groove and a wheel with a wider face may be a better choice. The same wire wheel used for interpass cleaning can also be used to clean the finished weld and remove any slag from the cap pass.
Weiler’s wire wheels feature a dual-hex nut design that makes it easier to flip the wheel occasionally, which helps promote the self-sharpening ability of the wire tips. This delivers optimal cleaning action and longer life while improving safety. Cleaning between weld passes can also be done with an encapsulated stringer bead wheel where only the wire tips are exposed. These brushes can provide longer product life and aggressive cleaning action, but they offer the user less flexibility because of the short trim length of the wires.
Tips for success
With any abrasive product used to prepare and clean pipeline welds, following some key best practices will result in safe, efficient use and optimal results. Implementing these six tips will make a difference in achieving proper weld penetration.
1. Focus on proper weld prep and cleaning. The more thorough the prep and cleaning, the fewer problems when it’s time for weld inspection. Proper weld prep and cleaning help reduce weld inclusions and costly weld failure. Ensure that all pits and rust are removed from the pipe bevels just prior to the pipe being set and tacked for prep of the root pass.
2. Match speed and size. The wheel or disc should fit the tool and have an RPM rating that meets or exceeds the tool’s RPM rating for safest use. Just because a product fits onto a specific tool doesn’t mean it was designed to be safely used with it. Using tools and products that aren’t designed for the job introduces safety risks and can result in poor weld quality.
3. Use the product as designed. Not all 1/8-in.-thick wheels are the same. Some are designed to be used vertically while others are designed to be used for grinding, as well. Always check the manufacturer’s recommendations and never use a wheel designed only for vertical use to face the land or transition pipe.
4. Avoid using too much pressure. To get the most efficient and safest performance, use the proper pressure and avoid aggressive pushing. With a wire brush, excessive pressure bends the wires so that the sides, rather than the wire tips, hit the weld. This reduces cleaning power and increases the chances of long wire breakage, increasing safety risks. Let the brush tips do the work as they are designed. With grinding wheels, pushing too hard can produce more heat, breaking down the wheel faster or causing glazing.
5. Don’t notch a grinding wheel. Grinding wheels with a harder bond tend to load, which refers to base material accumulating on the wheel due to the heat of the grinding process. Some operators form chips or notches around the wheel’s edge to clean a wheel that loads, but this is a dangerous practice that can result in flying debris. Instead, look for a grinding wheel with the appropriate bond strength for pipeline welds.
6. Always store abrasive products as directed. Proper storage and handling helps optimize their performance and extend product life. Store them in a clean, dry place and avoid laying them on the ground in wet or muddy conditions.
When welders choose the right abrasive products for pipeline weld prep and interpass cleaning and follow key best practices, they can reduce their rework and improve the overall results in these critical applications. After all, the foundation for a high-quality weld is laid from the very beginning – taking the time for proper prep and cleaning at the start of the process can save time and money later.
