Flanges are used in petrochemical, oil and gas, power generation and other industrial applications to connect pipes, valves and pumps. Pipe flanges connect piping systems and allow for efficient flow of liquids or gases. The proper selection, installation and alignment of flanges is critical in preventing leaks and damage to the system. Flanges, like most components, can be damaged due to poorly fitted gaskets, excessive vibration, corrosion or improper installation. Any of these factors can lead to serious system failure, causing thermal shock, excessive loads, stress shocks or stress cracking corrosion, resulting in excessive lateral or rotational flange misalignment. When performing maintenance, a previously assembled flanged joint can spring out of alignment in any direction around its circumference.
When performing pipework, there must be a seamless connection from one pipe to another between flange joints. To ensure a leak-free fit, flange joints must be aligned properly with the correct tools. This is accomplished by using a flange alignment tool when simultaneously attaching both flange joints.
Even while in service, misalignment of a flange may not be noticed until a joint leaks-- most often due to excess vibration or corrosion of the flange or bolts.
Special flange alignment tools are used when a flange needs to be replaced or realigned. It is not as simple as pounding them into place and wrenching the bolts to line them up. Imagine a pipe flange as a car's wheel hub. When replacing a wheel, the thread studs on the wheel hub must carefully align. The nuts are tightened in an alternating pattern to ensure a properly seated fit. If not installed correctly, the wheel will become misaligned and can break off when driving.
When assembling or reassembling pipes during construction or maintenance, flange alignment tools are used to align or re-align flange joints. The tool attaches to the flange joint where there is the greatest misalignment and then it pulls, pushes or slides the flange into place, so bolts are aligned for proper assembly. Many alignment tools are available to suit the specific application. The majority of these tools use mechanical force to align the mating flanges. However, in some large pipe applications, the flange alignment tool is usually operated hydraulically.
THERE ARE FOUR COMMON TOOLS FOR PROPER ALIGNMENT OF PIPE FLANGES
#1 - Flange Alignment Pins
Available in various sizes to accommodate the flange holes, these pins have a tapered shaft to create an easy fit. Two pins are placed into closely aligned holes on opposite sides of the flange and rotated 180 degrees to force the holes to line up and slide the flange into place. This secures the flange while bolts are inserted into the remaining holes and properly torqued down. Next, the alignment pins are removed by rotating them 180 degrees in the opposite direction. After the pins have been removed, the alignment pin holes are secured with flange bolts.
#2 - External Alignment Tools for Flanges
The most well-known style is that of industrial tool manufacturer ENERPAC. These easy to use tools are handheld devices available in three styles:
- Two mechanically-driven styles:
- One for small flanges, requiring minimal pressure to align the holes
- Another for large flanges that require up to four tons of force to make alignment
- A large hydraulically-driven style that provides up to ten tons of force
These alignment tools move the flange at the point of greatest misalignment, making it easy to maneuver in tight spaces.
Follow these steps when using this type of flange alignment tool:
- Attach the tool at the location of the greatest misalignment.
- Use the accompanying strap to wrap around the pipe, securing the tool to the flange.
- Rotate the screw handle until contact is made with the flange circumference.
- Continue to rotate the handle, tightening the strap until the flanges are pushed and pulled into alignment and the holes match up to accept the bolts.
#3 - Pipe Flange Aligners
When constructing new pipework, pipes do not always have flanges attached. If flanges or adjacent pipes are corroded or damaged, new flanges must be attached during maintenance. In both cases, new flanges are welded to the mating pipes. Before welding, a pipe flange aligner ensures horizontal and vertical alignment of a new pipe flange. The aligner is a rod with an embedded level that runs between two pins for horizontal alignment. One of the pins has another embedded level for vertical alignment. The pins are placed into mating flange holes. The flange is then leveled out at both the horizontal and vertical positions. Once the flange is in proper alignment, the welder tacks the flange into place. The tool is used again to ensure everything is aligned properly prior to permanently welding the flange to the pipe.
Internal Flange Alignment Clamps
Internal flange alignment clamps are used to precisely align small flanges to mating pipes. They quickly and precisely align the ID of the flange to the ID of the pipe and are typically used to align flanges, such as weld neck and slip on types, prior to welding them to the pipe.
These expanding scissor-type devices are often called Spider Internal Pipe Alignment Clamps. They ride on a threaded rod with a manual knob on the end. The forward clamps insert into the pipe and expand to fit the ID while turning the knob. Once fully expanded to the pipe ID, the back scissor-type clamps collapse to allow the flange to slip on. The back clamps are then expanded by turning the knob until the flange and pipe are tightly aligned and ready for welding.
Conclusion
Pipework is a difficult job that requires extreme precision. This is especially true when connecting large pipes. There is no margin for error in connecting pipe flanges, due to the risk of gas or high-pressure liquids escaping. Pipe flanges may become misaligned if they are not well constructed or from vibration over time. Too often, maintenance personnel will loosen the bolts of a misaligned pipe and use a mallet to force the flange back into place and over-torque the bolts when retightening. The shock on the flanges can cause the welds to crack. Forcing the bolts back into place by over torquing causes fatigue on the bolts, which can eventually fail due to reduced tensile or shear strength. These shortcuts can lead to pipe failure and the costly downtime. This reinforces the importance of using a pipe flange alignment tool to ensure a secure and leak-free fit.
Sources Include:
- Enerpac Tool Group #1
- Enerpac Tool Group #2
- Specialty Maintenance Products
- Piping Engineering #1
- Piping Engineering #2
- What is Piping
