The Equity Engineering Group Inc. (www.equityeng.com) specializes in risk management for petroleum, natural gas and chemical processing industries. It helps its clients to avoid property damage and business interruption through the early detection of equipment problems. By analyzing existing and new equipment for structural adequacy, code compliance and remaining-useful-life using materials science, metallurgy, corrosion engineering and mechanical engineering, the company identifies potential trouble spots before equipment fails and decreases maintenance expenses while preventing unscheduled outages.

"When we assess crack-like flaws during fitness-for-service investigations, the state of welding residual stresses are very important," said David Osage, president and principal engineer of Equity Engineering, in an interview.

"Not only do we have to predict stresses from pressure and from external load, we also have to make an estimate of what the residual stress is through the wall thickness at a weld joint. Typically, residual stress is a function of heat input, number of passes, joint geometry, and several other factors."

One of the tools Equity Engineering uses is the finite element analysis (FEA) software that design engineers use in studies of loads on their products. Design engineers use finite element analysis on products that range from aircraft to zippers.

Since early 2006, Equity Engineering has used a finite element analysis package based on Battelle's Verity mesh-insensitive structural stress methodology. This package was developed to calculate the fatigue lives of structures and welded joints. Battelle (www.battelle.org) licensed its Verity method to Safe Technology, which produced a new add-on module called fe-safe (www.safetechnology.com/fe-safe.html). The fe-safe software can be applied to structural welds in thick plate, seam welds in thin sheets, and spot welds.

In cost to industry, fatigue is one of the biggest failure mechanisms after corrosion, Osage said.

Most fatigue damage in processing industry equipment occurs at the welds. Using software-based stress analysis tools improves the initial design of equipment and adds accuracy and confidence to predictions, and also helps to inform maintenance judgments.

Osage said a common question is: Do I shut down now and fix it, or can I run another two years, schedule a shutdown, and fix it right? Sometimes a shutdown can cause more damage than leaving the system running, even if it has with a small problem spot. Some pieces of equipment take a week just to shut down. Running an analysis through a computer eliminates "best-guessing" and potential disasters.

Osage conservatively estimated that the use of Verity/fe-safe software saved his company's refinery customers as much as $10 million a year, while also providing data that confirms a level of facility safety and accountability to public interests.