O&M

The Right Valve for the Job

Why grooved is the better choice for fluid and gas flow control in today’s power generation facilities

Why grooved is the better choice for fluid and gas flow control in today’s power generation facilities

BY STEVE MORRISON

Tens of thousands of valves are required to manage the myriad of fluid and gasses in a power generation facility. Whether the valve is for isolation, flow reversal protection or something completely different, engineers and designers face endless safety considerations and performance options when selecting valves. Decision makers must choose a valve capable of accommodating the demand and stress placed on these plant piping systems.

To truly understand the best valve solution for an application, owners, engineers and contractors must work together to evaluate product design, performance, quality and lifecycle costs to select the most appropriate product for their needs.

Transportation of grooved pipe spools is more efficient, reducing trips, site congestion and shipping costs.
Transportation of grooved pipe spools is more efficient, reducing trips, site congestion and shipping costs.

Design and Planning

During the design and planning phase, it is important to accurately specify the system parameters as well as media and flow conditions through the hydraulic circuit. Only then can engineers select the appropriate hardware solution to meet configuration, material and other system requirements.

One of the most commonly overlooked elements when designing and planning a pipe system for power generation plants are flow rates and Cv values. It is imperative that the right valve size and type are selected to enable peak performance. Improper valve selection can be both costly and risky. If a valve is too small, it will not pass the required flow, and the process will be starved. Alternatively, an oversized valve unnecessarily increases costs.

The Cv value – the uniform measurement of liquid flow capacity coefficients – is vital in any planning scenario for power generation plants because it is directly related to operation costs from power consumption of electric motors used to operate pumps. This is invaluable as more flow at a lower pressure equates to less energy needed for the pipe system to overcome the pressure drop.

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The Grooved Solution
A grooved pipe joint comprises four elements: Grooved-end pipe, gasket, coupling housing and bolts/nuts.
A grooved pipe joint comprises four elements: Grooved-end pipe, gasket, coupling housing and bolts/nuts.

Full Speed Ahead

Anyone who has been involved in a power plant project knows that the construction schedule is one of the most important, and most challenging, aspects of a project to manage. Companies often push for an aggressive timeline in hopes of reducing labor costs and activating their new facility as quickly as possible. However, fast-tracked schedules can lead to a variety of problems, including reductions in work quality, unbudgeted overtime and missed deadlines.

Recent advances in design and information technologies have proven the value of prefabrication as a strategy for cutting installation times and improving overall project efficiency. When properly implemented, prefabrication can reduce installation labor costs, while reducing congestion at the construction site and allowing for more efficient component assembly.

Consider the Connection

Consider flange and mechanical-groove connections, as end-connection is an important factor when determining the optimal system designs. Unlike flanged valves, grooved-end valves can be assembled onto pipe spools under the controlled conditions of a fabrication shop, drastically minimizing joints made in the field, reducing labor costs and time in both the shop and field. The manner in which a flanged joint holds a seal is sensitive, particularly in transport, where damage can often occur. On a grooved-end valve, the seal is on the outside of the pipe and the mechanical coupling carries the load, mitigating concerns about weakening the seal during transportation.

In transport, pipe spools designed with mechanical-groove valves can be kept in one plane-what’s known as two-dimensional fabrication, and segments can be rotated into their 3D position on site. 2D spools may include a linear length of pipe, valves and fittings all connected in a flat pack type of configuration. This makes the spools easy to load and enables an increase in the linear footage of pipe on a truck (Figure 2). In fact, it’s possible to load up to three times more 2D spools than 3D spools on a single truck. This makes transportation more efficient, minimizing trips to and congestion at the construction site, resulting in reduced shipping and jobsite handling costs.

Systems designed with grooved-end valves generate time savings and other benefits in the fabrication shop as well as the field.
Systems designed with grooved-end valves generate time savings and other benefits in the fabrication shop as well as the field.

Systems designed with grooved-end valves generate time savings and other benefits in the fabrication shop as well as the field. In the ideal shop environment, fabrication and assembly of grooved pipe spools, including valves, has been shown to increase total shop throughput to 48 diameter inches or more per hour.

Once at the job site, the benefits offered by mechanical-grooved valves over flanged valves in prefabricated pipe segments become obvious. One painful example stands out: hoisting a pipe spool off a truck that includes a flanged valve creates stress and stretches the flange hardware, calling into question the integrity of the joint. By contrast, pipe spools featuring grooved mechanical valves can be lifted with confidence, because the stress is carried across the ductile iron body of the mechanical coupling and not on the hardware itself.

Reducing Risks and Associated Costs

Costs of installation and maintenance are other notable risks to consider when designing a flow control strategy. Grooved-end valves provide added benefits considering the speed and ease of which they can be installed and maintained. Mechanical-groove valves also eliminate the need for unions or other access points, reducing the total number of joints necessary to build and maintain the system, minimizing the system footprint and total installed cost.

Another recent innovation in grooved-mechanical valve design integrates pipe joining capabilities into the body of the valve itself. A knife gate valve has been introduced that provides, not grooved-end pipe connections, but mechanical couplings integrated into the body of the valve itself. This new design delivers a solution that reduces the number of components and install-time, delivering increased efficiency in the field and new prefabrication opportunities.

Prevailing technology requires that large knife gate valves be removed from service in order to be maintained or rebuilt, requiring riggers, electricians, and mechanical contractors working together to complete the often challenging task. An alternative maintenance method has also emerged that removes these risks and delivers a predictable maintenance cost, allowing all of the serviceable components of the valve; knife, packing gland, retaining plate, knife seal, seat and seat gasket, to be replaced as one pre-assembled seat cartridge. Innovations like these are changing the landscape and setting higher expectations within the construction industry.

Breaking with Tradition

Despite the availability of emerging technologies and the clear benefits they offer, less than optimal design solutions continue to be specified. Owners, engineers and contractors should consider a few more facts that add weight to the evidence favoring grooved flow control solutions over flanged.

Victaulic, a leader in pipe joining and flow control, offers grooved end valves that weigh one-third less than its comparable flanged valves. The grooved solution also provides a greater pressure safety factor and the weight difference makes it easier to handle and install – adding to the space and weight savings are gains in speed that come from installing a grooved valve versus a flange valve.

Ultimately, offering a higher ROI is the greatest market disruptor. Even in projects as massive as power generation facilities, choosing the right valves from the beginning matters. Like the right tools on a belt, the right pipe joining and valve solutions can simplify installation and maintenance scenarios, reduce constructions schedules and improve the ROI of a project by diminishing downtime and profit loss.

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