By Luke Prinsloo
Safety is non-negotiable, which is the reason why engineers historically have taken a “belt and suspenders” approach to developing system designs for exacting operating conditions. Traditionally, designing for the anticipated stresses, strains, and loads over the service life of an asset or installation has meant going big in terms of secondary reinforcements, pipe wall thickness, valve, and fitting selection, and buried depth, all of which are predicated on boundary conditions such as pressure and temperature. This approach unarguably produces safe and reliable structures, but it also often results in higher costs, a larger footprint, and a longer and more complicated installation process.
For example, it is typical for high-temperature requirements to be applied across an entire aeration system. The whole system is designed for 300°F requirements even though some areas, like the blower room, may only see a maximum temperature of 250°F, and the branches may only see 200°F. Designing to a higher standard impacts valve material selection, expansion joint selection, and material selection, all of which impact the bottom line. Similarly, following AWWA M11 to design fully restrained mechanical joints that accommodate thrust for buried pipelines requires the installation of many large rods and gussets, which drives up both capital costs and installation time.
Without a deeper understanding of the stresses and loads of a piping system, the safest approach is to design to recognized standards even if that means designing well beyond the conditions the system will experience over its working life.
Optimized designs deliver value by substantially mitigating the direct costs of construction which include the equipment needed to manage components on site, the materials used, and the labor required for installation. The challenge engineers face is that developing an optimal design is difficult when the designer is working with limited information, and in the interest of safety, is developing a design based on worst-case scenarios.
Stress analysis can change that paradigm by enabling a mathematically based understanding of a system’s performance while in use to provide insight that allows the development of safe alternative designs. In simple terms, stress analysis is an early investment that reduces potential risks and reduces costs through optimization.
Making this investment at the front end of a project is a long-term investment because it not only enables better system design, but it delivers value over the life of the asset through simplified operation and maintenance.
Benefitting from stress analysis
In most cases, designs are determined by customer specifications that are dictated by performance needs, site conditions, regulatory requirements and guidelines, and industry standards. Unfortunately, a design that is appropriate, safe, and executable may also include design constraints that can lead to unnecessarily high construction and maintenance costs. And once a design is developed and approved, the last thing engineers and contractors want to see are changes because every alteration to the approved plan means more time and more money.
Stress analysis allows designers to uncover the limitations or shortcomings in a design and pinpoint areas for optimization. In some cases, improvements can take the form of product substitutions; using alternative components that deliver the same or better performance. In other cases, the results of the analysis are the foundation for major redesigns.
Stress analysis uses standard software tools like Ceasar II or Autopipe to look at loads inside of the piping to understand the loading that takes place during the construction of large systems. Using this software, analysts can identify things such as supports that are designed for more robust performance than what is required and instead reinforce an elbow or tee to handle the anticipated loads.
The more complex a system, the greater the value derived from stress analysis. When a system needs to accommodate dynamic movement, understanding the unique stress challenges of the project provides the framework for designing a system that meets those demands most efficiently.
The other critical component is partnering with analysts that have the breadth of experience and depth of expertise to know what substitutions and redesigns are valid for a particular project. Victaulic provides this input through a team of analysts with backgrounds in different industries who deliver a broad view and a deep understanding of solutions and their potential application. Exposure to regional rules, regulatory guidelines, and requirements in different parts of the world is an advantage when problem-solving and allows the team to capitalize on the experience of the individual members. Sometimes, a solution that works well in one region or industry can be transferred easily to an area where it has never been applied.
Delivering value through simpler designs
In a recent project, the Victaulic team performed stress analysis on a proposed piping system design that was being considered for an airport in the Middle East. The complex design developed for the airport had to accommodate seismic and thermal movement as well as the curvature of the building.
The original design was massive. Nearly every spool of pipe included either mitered elbows or pre-curved 36-in. pipe spools to accommodate the architect’s design. Performing stress analysis allowed the team to replace the cumbersome design that was laden with many components and custom fittings to accommodate the curvature of the building with a simplified layout that incorporated easily sourced flexible mechanical pipe couplings. With these pipe couplings, the entire chilled water process piping system could be constructed using standard spool lengths, which allowed for simpler laydown and material handling. Stress analysis also revealed that fewer anchors and guides were needed to meet the seismic requirements for the system as compared to those dictated by the original engineering specification.
Another recent stress analysis program enabled refinements to a fire suppression system design that was to be installed on multiple bridges in a major metropolitan area. In this case, stress analysis was mandated because of safety concerns surrounding the load ratings on the existing bridge structures where dry fire suppression systems were to be retrofitted. In addition to the structural constraints, the design considerations included wind, slug flow, pressure thrust, and seasonal temperature changes.
Taking these parameters into account, the team of engineers who performed the stress analysis determined that appropriately placing loops in the system would lower slug forces, which would allow simpler, cheaper anchors to be considered. Using this approach simplified the design by eliminating nearly 30 anchors across five installations, leading to a savings of $250,000 USD on the anchors alone. Flexible pipe couplings for the curved bridge sections enabled the contractor to simplify the support and installation scheme for the bridge, which expedited construction and lowered costs by reducing the number of fittings and eliminating custom spools without compromising safety.
As this was an active roadway, work was carried out at night to minimize traffic impacts, meaning every hour saved in construction had a significant impact on the total installed cost of the fire safety system.
Making the move
Stress analysis is commonplace in other industries where designers rely on technology to gain crucial insights into the effect of design parameters, improve design accuracy, shorten the design cycle, reduce construction cost, and minimize the footprint of installations.
Adopting analytical methods to determine the best design enables efficiencies across the board by delivering project certainty and mitigating risk. Some companies may balk at making this front-end investment, but a growing body of work proves that stress analysis pays dividends in risk reduction and improved system performance, also saving time and money.
Luke Prinsloo, P.E., is a piping system design engineer at Victaulic, a leading provider of mechanical pipe-joining solutions since 1919. Contact him at Luke.Prinsloo@victaulic.com