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HPAC Engineering

Piping-System Design Impacts Project Safety

Oct. 1, 2008
The first fundamental canon of the American Society of Mechanical Engineers' Code of Ethics of Engineers states, Engineers shall hold paramount the safety,

The first fundamental canon of the American Society of Mechanical Engineers' Code of Ethics of Engineers states, “Engineers shall hold paramount the safety, health, and welfare of the public in the performance of their professional duties.”

Because of the nature of construction work, this can be a major challenge. According to the Bureau of Labor Statistics, the construction industry has the second-highest rate of injury cases resulting in days away from work (Figure 1).1 More specifically, statistics compiled by the Construction Industry Institute indicate that pipefitters, welders, plumbers, and the laborers who assist them suffer the majority of construction injuries (Table 1).2

The inherent dangers associated with installing and maintaining piping systems increase the importance of a mechanical engineer's role in designing for safety and accident prevention during project construction and throughout a facility's life cycle. There are three fundamental areas in which mechanical engineers can affect safety positively: system constructability, best practices for training construction and inspection, and system maintainability.

By specifying safer technology and methods in greater detail, an engineer can minimize the impact of, or possibly even eliminate the potential for, certain types of accidents and injuries. Although most injuries on job sites and in the workplace occur via material handling, the most significant risks — in terms of potential impact on people and businesses — are caused by fire and fume hazards.


In the piping-systems environment, mechanical pipe joining removes a number of major hazards from a job site. The most obvious dangers include the presence of fire and toxic-fume hazards associated with welding, brazing, and soldering. When grooved, stab (plain end), or press pipe-joining technologies are used, open arcs, sparks, and flames do not occur, and volatile tanks, lead lines, and hazardous fumes are not a problem.

By specifying mechanical pipe joining, an engineer can reduce these risks during the design phase, contributing to a reduction in an owner's risks, costs, and potential liability. Further, in keeping with holding “paramount the safety, health, and welfare of the public,” an engineer can help create safer environments. For example, in addition to the inherent risks of fire, potential health risks associated with welding include irritation of the eyes, nose, chest, and respiratory tract; nausea, headaches, and dizziness; metal-fume fever; lung cancer; urinary-tract cancer; heart disease; kidney damage; and Parkinson's disease.

Depending on the project environment (e.g., new construction vs. expansion/retrofit), these hazards can become a risk not only to construction workers, but to the occupants of the structure and surrounding facilities. The initial use of traditional joining technology can limit the maintenance options for, or efficiency of, future repairs, replacements, and retrofits.

Although there are established procedures and requirements for fire prevention and fume ventilation during welding, unfortunate incidents involving welding are not uncommon. Consider the potential risks concerning the retrofit of a hospital or school, where occupants may not be evacuated easily or protected from these risks. To protect people from these hazards, construction schedules often must be rearranged and extended to allow off-shift work when buildings are unoccupied. Eliminating hotwork when possible reduces risk for clients, occupants, and contractors.


In addition to enhancing safety by specifying pipe-joining technology, an engineer can contribute to safe environments by defining best practices in product selection, training, installation, and inspection.

Product selection

Performance-based specifications typically provide a good general scope of acceptable product and system-performance requirements. In addition, engineers can name specific manufacturers that they consider to be acceptable because of their quality and service.

Although it often is assumed that an engineer must specify three manufacturers for a product or system to ensure his or her objectivity, legal precedents supporting a specifier's right to issue a proprietary specification designating a sole supplier in certain situations have been set at the District Court level. In the 1974 case Whitten vs. Paddock, the U.S. District Court of Massachusetts established that:

  • Proprietary specifications do not violate antitrust laws.

  • Few brands of products are exactly alike, and specifiers who want to limit choices have every right to do so.

  • Other brands qualify as “or equal” only when the specifier says so.

  • The specifier may waive specifications to obtain a more desirable product for the end user, but the specifier is the only one who can determine if the product is more desirable.

  • The burden is on the non-specified manufacturer or supplier to convince the specifier that its product is equal for the purpose of a particular project.

This gives specifying engineers even greater project control and enables them to ensure high quality and system performance for their clients.


An engineer can influence installation quality by ensuring that individuals installing systems are educated about proper installation requirements in accordance with manufacturers' published instructions. Specifications can require installing contractors to obtain training directly from a manufacturer.

Inspection and test procedures

An engineer can ensure that acceptable systems are delivered by detailing mandatory inspection and test procedures in mechanical specifications. Selecting products and systems that are easy to install and inspect further increases the chances of successful startup. For example, some grooved-coupling manufacturers provide for quality control through visual confirmation of complete coupling installation. Complete joint installation is verified easily because the coupling is designed so that the completed joint achieves metal-to-metal bolt-pad contact. Welding, on the other hand, requires X-rays for quality inspection.

System testing is an important practice typically detailed in specifications to ensure system performance. Specifying that manufacturers' product-performance ratings allow for proper hydrostatic system testing (typically 11/2 times the system operating pressure) helps to ensure system integrity.


Over the operating life of a facility, a piping system will require three basic categories of maintenance: routine periodic inspection, physical changes or expansion, and unscheduled repairs. Because of its intrinsic design qualities, grooved mechanical pipe joining makes maintenance and system access easy, fast, and safe, minimizing downtime and other negative impacts of maintenance events.

Uncomplicated system access gives grooved mechanical pipe joining an advantage compared with welded pipes. When pipes are welded together, there are no union points. In effect, the pipes become a single, extended piece of metal. However, a grooved coupling provides a union at every joint, which allows easy system access and flexibility for future system expansion. To access the system, a maintenance worker unscrews one or two nuts, and the pipe section drops out. No torches, saws, or welding machines are needed. Even with flanged-, lug-, or wafer-type valves and accessories, the compression of flanged connections can create significant maintenance challenges that increase the time and manpower needed for replacements and repairs. Welded components can be difficult to remove and often even more challenging to reinstall.

When maintenance is complete, a mechanical coupling can help get a system up and running again quickly. The gasket is reinstalled, the coupling is placed back on the pipe, fitting, or component, and the bolts are tightened. In a welded system, repairs and maintenance demand that workers cut out the damaged pipe section and weld it back together, causing potential operational issues and safety hazards that are particularly significant in existing facilities and occupied spaces.


As with any engineering challenge, all system characteristics and design options must be considered thoroughly to find optimal solutions. There are some applications, such as steam services, for which grooved piping systems are not suitable and weld/flange systems are required.

It is imperative that the performance capabilities of systems and products meet system-performance requirements. For example, proper gasket material and design selection are important elements to ensuring the safe, long-term performance of a grooved mechanical system. Advances in elastomer technology and innovative coupling and gasket designs provide performance in water applications with temperatures up to 250°F and pressures from absolute vacuum up to 1,000 psi. However, not all gaskets, couplings, and components are equal in performance, and the capabilities of each manufacturer and product must be evaluated individually to confirm system and client requirements are met.

The engineer has a vital role in improving safety at every stage of a project's life cycle from initial design to installation to ongoing maintenance. Nothing is more paramount than the safety, health, and welfare of the public.


  1. Bureau of Labor Statistics. (2006). Workplace injuries and illnesses in 2005. Washington, DC: Bureau of Labor Statistics.

  2. Hinze, J. (1991). Indirect costs of construction accidents. Austin, Texas: Construction Industry Institute.

The director of training for Victaulic Company Inc., John Rutt has an extensive background in the commercial HVAC market and is responsible for developing and implementing the training, ongoing-education, and professional-development programs for the company's global sales organization and piping-industry professionals. He received a bachelor's degree in mechanical engineering from the University of Pittsburgh.