Mechanical engineers can choose from numerous pipe-joining methods when designing commercial plumbing, heating and air systems, each with their own advantages and disadvantages. The final joint selection is critical to system effectiveness and efficiency, as it directly impacts construction, commissioning and maintenance processes.

Part 1 of this series, which was published in Plumbing Engineer’s April 2024 issue (https://bit.ly/3Rg6k6X), covered the following pipe-joining methods:

• Grooved joints. Contractors may employ a roll or cut grooving technique to prepare grooved pipe. They create joints by stabbing a coupling onto grooved pipe ends and using standard hand tools to secure bolts. 

The benefits of grooved pipe-joining solutions include ease and speed of installation, increased safety due to the elimination of hot works, the ability to visually verify for proper installation, improved pipe access during and post-installation, and minimal maintenance. However, contractors may face higher material costs when using this method.

• Welded joints. Certified welders use torches to fuse pipe metals, creating a permanent joint. Welding creates strong pipe connections, eliminates the need for additional materials to create seams, allows for the joining of two different piping materials and may help streamline the insulation process. 

Pitfalls of welding include the need for extensive coordination; exposure to potential safety hazards, including fire, sparks, slags and fumes; time inefficiency, especially as pipe diameters increase; and difficulty with altering or expanding systems post-installation.

• Flanged joints. Fitters place flange faces and gaskets on pipe ends, then follow a bolt-tightening sequence with specific torque requirements to secure four to 20 bolts, creating a tight seal with an even load distribution. Like grooved solutions, flanged pipe-joining methods are safer than welding due to their flame-free assembly and not requiring specialized craft workers for installation. 

However, specialty equipment is required, and installers must meticulously follow tightening instructions, which can be tedious and time-intensive, especially for larger pipe diameters that require more bolts. Additionally, flanged joints require regular inspection and maintenance to ensure bolts don’t lose their grip or that pipe movement is not causing cracking or bulging, leading to system failure.

Part 2 discusses threaded, brazed, soldered, and compression joints.

What Is a Threaded Joint?

Installers screw together male and female pipe ends to create threaded joints. Threaded systems are most suitable for low-pressure and low-temperature applications. This method is commonly used in pipe diameters 2 inches and smaller.

• Features. Threading is a flame-free pipe-joining method, although the initial pipe preparation process can be messy. These connections are easy to take apart for maintenance or alterations, and assembly requires no specialized certifications or equipment. Threading is compatible with various materials, including cast iron, copper, PVC and galvanized iron systems.

• Installation. Pipe preparation is the first step to installing a threaded connection. Pipefitters must cut pipe to size and use specialty equipment to create threads, a step typically performed at a staging area away from the active work site. Threaders require lubricating oil and generate metal shavings, which crews are responsible for cleaning up at the end of the day. 

Once ready, materials are transported to the installation area and secured with wrenches. Installers must be careful to ensure proper thread engagement without overtightening, as that can damage or strip threads, increasing leak risk and repair costs.

• Maintenance. Threaded systems require regular inspection to check for wear or corrosion. In-house personnel can easily perform maintenance, making threaded systems affordable to replace and maintain.

What Are Brazed and Soldered Joints?

Similar to welding, brazed and soldered joints use heat to join pipe. Unlike welding, where welders fuse pipe ends, brazing and soldering involve melting filler metal to bond copper or copper alloy pipe. The filler material dictates the melting point, which is where the two techniques differ:

Brazed joints melt metal at temperatures exceeding 840 F. The high temperature required to join pipe ends makes brazed joints stronger than soldered ones.

Soldered joints melt metal at temperatures below 840 F.

• Features. Brazed and soldered connections offer mechanical strength and durability benefits. They yield strong bonds even when joining dissimilar metals and are performed at lower temperatures than welding, reducing the risk of warping or overheating.

• Installation. Brazing and soldering must be performed by certified professionals and in accordance with local building codes. Similar to welding, additional safety precautions are necessary to protect construction teams and property. 

System designers must specify the filler materials to meet pressure and thermal ranges, along with expansion and contraction requirements. Then, installers use hand torches to melt the specified filler metal. Pipe cleanliness is critical to the brazing and soldering process, as contaminants can impact bonding.

• Maintenance. Brazing and soldering are permanent joining methods that should be regularly inspected for defects, wear and tear, and corrosion. Qualified professionals must perform any system repairs or alterations.

What Is a Compression Joint?

Compression joints connect plain-end pipe and comprise three components: compression nut, ferrule and fitting. System designers can use compression fittings to join plain-end pipe of different materials and sizes without applying heat.

• Features. These joints generally have a low installation cost because of their minimal pipe-end preparation. However, additional joining methods may be needed to meet the pressure flow needs of different system areas. Compression joints are quick to install and instill confidence in joint integrity due to the tooling method used.

• Installation. Fitters can start assembling compression joints once pipe ends are clean. First, they will place the compression nut and ring on the pipe, insert the pipe into the fitting, and finally tighten the nut using a tool to create the seal. 

The disadvantage of this method is it requires assembling multiple components, a process that can require significant installation time on sizable projects. If leaks occur, maintenance staff can easily tighten the connection to address the issue. Overtightening, however, can cause damage to the joint.

• Maintenance. Compression joints should be regularly inspected for signs of wear and corrosion. Specialty contractors are not needed to perform maintenance or alterations on these connections.

Looking to the Future of Pipe-Joining: Prefabrication

The pipefitting industry is progressively shifting to prefabrication and modularization strategies, especially as buildings grow in complexity and construction schedules shorten. Economists predict the global modular construction market will grow at a 6.20% compound annual growth rate over the next five years. 

Connecting pipe in off-site controlled environments enables mechanical contractors to reduce risk, increase installation speed and better monitor joint quality, improving the overall project. 

Fabrication cells can be equipped for various joining methods, ensuring bolstered jobsite productivity for different system requirements. Contractors can further enhance their time savings by combining prefabrication strategies with innovative pipe-joining technologies designed to reduce installation times. l

Mark Gilbert is vice president at Victaulic, a global manufacturer of pipe-joining, flow control and fire protection solutions for the most complex piping applications. Contact applications.engineering@victaulic.com or visit www.victaulic.com to learn more.