Two of the most important elements in any construction or upgrade project are safety and speed of completion. While one way to increase safety is to eliminate hot work whenever possible, the reality is that welding is necessary for many tasks around a power plant. However, one area where welding may not always be required is in the installation or expansion of piping systems.
Although the pipe-joining method is critical for high-pressure, high-temperature process piping systems, the same cannot be said for balance-of-plant piping systems. Services such as cooling water, reverse osmosis, fire protection, chemical treatment, lube oil, and compressed air can make use of alternative, flame-free joining methods—some of which can offer installation up to 10 times faster than welding. Grooved mechanical piping is one of those alternatives.
A Novel Design
A grooved mechanical pipe joint consists of four elements: grooved-end pipe, a gasket, coupling housing, and fasteners. The pipe groove is made by cold forming or machining a groove into the end of a pipe. A gasket enclosed in the coupling housing is placed around two abutted grooved pipe ends, and the key section of the housing engages the grooves. The bolts and nuts are tightened with a socket wrench, or impact wrench, holding the housing segments together.
In the installed state, the coupling housing encases the gasket and engages the grooves around the circumference of the pipe to create a leak-tight seal in a self-restrained pipe joint. In addition to pipe-to-pipe joints (Figure 4), grooved couplings can be used to join pipe to grooved-end valves, fittings, and accessories to create a complete piping system.
|4. A grooved mechanical pipe joint. This cutaway view shows the four elements of a joint: the grooved-end pipe, gasket, coupling housing, and fasteners. Source: Victaulic|
Roll grooving is the most common method for pipe-end preparation. The roll-grooving process radially displaces a small portion of the pipe wall, forming a groove around the circumference of the pipe that is recessed on the outside and indented on the inside. The method can be used on schedule 5 through schedule 80, carbon steel, stainless steel, copper, and aluminum pipe, ranging from 0.75-inch to 72-inch diameters.
There are two types of grooved couplings: rigid and flexible. Rigid couplings do not allow movement and can be used wherever rigidity in the pipe joint is needed, similar to a welded or flanged joint. Flexible couplings allow a limited amount of linear and angular movement to accommodate thermal and seismic movement as well as vibration and misalignment. The majority of grooved couplings used in power plants are rigid, with flexible couplings used only around rotating equipment to isolate noise or vibration. This enables the system to be supported and guided in accordance with the American Society of Mechanical Engineers (ASME) B31.1 Power Piping standard.
Safety, Speed-of-Installation Advantages
A key advantage of grooved piping is its flame-free installation. The assembly of a grooved pipe joint does not require welding, flame, or heat, nor does it produce fumes. In terms of preparation, there’s no need to remove or clean the surrounding area of combustible materials, and no need for increased ventilation or fire shielding. During assembly, torches and tanks are not required, nor are pipe fitters exposed to flame, sparks, slag, or fumes. There’s no need for a fire watch. As a result, grooved systems reduce risk to personnel and property.
Minimizing welding allows certified welders to focus on critical process systems while pipefitters handle the balance-of-plant systems, which can contribute to on-time completion of a project. Grooving pipe and assembling couplings do not require specialized certifications or training; the processes are easily taught and transferred.
These benefits were leveraged during construction of the South Hedland Power Station, located in the Pilbara region of Western Australia (Figure 5). With rapid growth requiring significant investment in power projects, the Horizon Power–owned facility chose grooved products due to a tight timeline and remote location. Selected for diesel fuel, raw/fire water, demineralized water, drinking water, and instrument air systems, grooved piping resulted in a fast, safe installation that eliminated the need for hot work and eased on-site pipe-end fabrication.
|5. A safe solution for many power plant systems. Grooved piping was used on several water, air, and diesel fuel systems at the South Hedland Power Station in Western Australia. Courtesy: Victaulic|
The safety advantages of grooved piping are complemented by the speed and ease of system installation. Standard grooved couplings can be installed up to five times faster than welded joints and three times faster than flanged joints. Ready-to-install couplings can double the time savings. Special tools are not required to assemble a grooved coupling, and most couplings do not have torque requirements. In addition, grooved systems provide visual confirmation of proper assembly.
Speed and ease of installation were instrumental during the construction of an Alstom gas-fired test facility in Birr, Switzerland (Figure 6). By joining the cooling and fire water piping systems with grooved couplings, valves, and fittings, Alstom was able to reduce installation hours 50% compared to traditional joining methods, resulting in considerable cost savings and faster project completion. The grooved components will also enable easy access for maintenance and repair.
|6. Installing grooved piping can save time. Alstom installed grooved piping at a facility in Switzerland, cutting installation time in half compared to welding. Courtesy: Victaulic|
Grooved couplings reduce maintenance downtime and, with a union at every joint, simplify system access, if needed. Couplings are easily disassembled and removed from the joint. Following completion of work, the coupling can be reassembled as quickly as initial installation. This characteristic eases maintenance, repair, and future expansions or modifications. When properly installed and operated within design specifications, grooved mechanical couplings are designed to last the life of the system and will not leak or fail.
Grooved systems bring a number of advantages to construction and upgrade projects, from quick, flame-free installation to simplified maintenance. Most importantly, grooved mechanical piping offers plant owners a means of speeding project completion while maintaining a safe environment. ■
—Mitch Lee is a business development specialist for the power market with Victaulic, a manufacturer of mechanical pipe-joining and fire protection systems. He is also a member of the Construction Industry Institute.