Nagesh Goel is the president and co-founder of Atlas Evaluation & Inspection Services (AEIS).

It’s commonly understood that infrastructure elements are regularly inspected by experts—failed inspections lead to unwanted costs and notoriety. Less understood is who performs such inspections as well as the role engineers can play to help the infrastructure they design pass their examinations and stay in use.

Nagesh Goel is a mechanical engineer with a graduate-level specialization in Non-Destructive Testing (NDT) and Metallurgical Failure Analysis. His career has focused on testing, inspection and certification of engineering materials and business systems, so he knows more than most about inspections and the role designers can play in them.

Basics of Inspection

According to Goel, owners envision a project; design teams help put that vision on paper through drawings and specifications; and construction teams build the project out. Inspectors act as the independent “eyes and ears” for the project, ensuring the construction is done as per the approved design documents.

“All construction is done as per established codes and standards built into the contracts,” he explains. “These codes and standards provide detailed limits on acceptance of flaws and issues. When no acceptance can be found, the design team provides the basis for acceptance.”

As an example, he describes the process for bridges.

“The Federal Highway Administration developed a bridge-inspection reference manual that details the fundamentals of bridge inspection,” says Goel. “AASHTO is another organization that has developed a manual for bridge-element inspection. These programs are adopted by all the DOTs, modified to suit their state requirements, and they usually commission bridge inspections every two years.”

He adds that any flaws are identified by an inspection testing agency, and, depending on their size and propagation from previous inspections, the flaws are repaired using pre-established and qualified procedures. All this work is done under the supervision of a structural engineer.

Inspection Specifics

There are two main types of infrastructure inspection: destructive and non-destructive. Destructive tests tend to be performed before the start of a project, seeking to find the limits of what a material can handle under the specified parameters. As an example, Goel describes a Procedure Qualification Test, which replicates the condition in which actual work will be welded.

“You take some test coupons, and they are welded with the same welding process: electrode, current voltage, speed, preheats and all different types of variables,” he explains. “The resulting heat inputs involved simulate very similar mechanical properties in the test coupon as the actual work. Then this test coupon is tested for soundness, ductility, trend toughness and other properties. If the result in properties meet the project specification and codes, then the same parameters can be taken for actual work, and you can expect to get a final product that meets the code requirements.”

Any test that doesn’t affect the end use of a product is termed an NDT method: the most common being visual inspection. Two additional common NDT methods are radiography x-ray and ultrasonic testing.

“Most failures occur when there is a weakness in the material, usually due to the presence of something we call a stress riser,” explains Goel. Stress risers include cracks, lack of fusion, undercuts in welds and notches.

How Engineers Can Help Themselves

Although Goel believes engineers are good at following the specifications to make designs safe, there are areas in which they can improve their methods to more likely pass inspections and maintain safe infrastructure. Designating a competent inspection agency is a key step.

“When you engage personnel for inspections, you must have people who are experienced in this work,” he notes. “Typically, standards stipulate a person should have such and such ‘certification,’ but you have to distinguish between certification and ‘qualification.’ Not every certified inspector is qualified to perform the work, and you’ve got to ensure the inspection teams you’re hiring have processes in place to approach your inspection and testing program, and they’re not just another company supplying certified manpower.”

Another important tip is to pay attention to the codes and design with them in mind.

“The code has different criteria for testing static structures work vs. cyclically loaded structures, but 95 percent of drawings do not differentiate which joints are statically loaded and which are cyclically loaded. It does not make sense to use the cyclic loaded criteria, which is much more stringent, for static reloaded structures or connections. It would make a big difference in actual inspection protocols if these were clearly laid out in drawings.”