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Maintenance & Repair

For Want of a Nail: Engineering Process Safety

“For want of a nail, the kingdom was lost,” is the final line of an old proverb that reminds us that seemingly unimportant acts or omissions can have grave consequences. An infamous example of this exists in one of America’s most tragic incidents, the 1986 Challenger shuttle disaster.

The Challenger exploded 73 seconds into its launch, killing all seven crew members. The investigation revealed that the disintegration of the entire vehicle began after an O-ring seal in its right solid rocket booster (SRB) failed at liftoff. The O-ring failure caused a breach in the SRB joint, allowing pressurized hot gas from within the solid rocket motor to reach outside and impinge upon the adjacent SRB attachment hardware and external fuel tank. This led to the separation of the right-hand SRB’s aft attachment and the structural failure of the external tank. Aerodynamic forces promptly broke up the orbiter.

There are many lessons learned from this disaster – but perhaps most importantly, that small components matter a great deal. This is one of the tenets of the work done at the Mary Kay O’Connor Process Safety Center (MKOPSC), which is named after Mary Kay O’Connor, a chemical engineer and plant supervisor who died along with 22 others in the Phillips 66 disaster of 1989. The accident at The Houston Chemical Complex (HCC) facility resulted from a release of extremely flammable process gases that occurred during regular maintenance operations on one of the plant's polyethylene reactors.

For Want of a Nail 2During routine maintenance, isolation valves were closed and compressed air hoses that actuated them were physically disconnected as a safety measure. The air connections for opening and closing this valve were identical, and had been improperly reversed when last re-connected. As a result, the valve would have been open when the switch in the control room was in the "valve closed" position. After that, the valve was opened when it was expected to stay closed and eventually passed the reactor content into air. More than 85,000 pounds (39 t) of highly flammable gases were released through that open valve almost instantaneously.

What began with a valve resulted in an explosion with the force of 2.4 tons of TNT. In 1997, Michael O'Connor founded the Center in memory of his wife to educate both engineering students and practitioners in the chemical industry to help prevent similar incidents and minimize the consequences of incidents. The center is linked to Texas A&M University, and has access to its experts in chemical engineering, chemistry, industrial psychology and other departments.

Chemical Process Safety

MKOPSC fulfills many roles in process safety with its underlying mission to make safety second nature. The center defines process safety engineering as “implementing into everyday engineering procedures, a broad-based understanding of the complex interaction of chemical process technology, mechanical and process design, process control, and Process Safety Management Systems (PSMS)”. Safety evaluation of an integrated petrochemical process includes identifying hazards, evaluating the risk from those hazards and finally identifying and evaluating cost-effective engineering solutions to reduce or mitigate those risks.

By working with educational institutions and major plant manufacturers, including those that make gaskets and valves, MKOPSC conducts various educational programs at the undergraduate, graduate and professional levels. The center leverages these relationships to obtain data and material samples to aid research into issues that affect the industry. For example, using state-of-the-art data mining methods, MKOPSC researchers were able to conduct trend analysis for incidents, research that led to the need for new materials research for valves and valve components.

Valves, Gaskets and Materials in the Mix

MKOPSC has researched relief valve installation and sizing, working to create simplified models for relief valve stability that move beyond the 3% rule while still being approachable and easy to use. Extensive research has been conducted across academia and the industry to determine what causes chatter and ways to prevent it in the hopes of improving the reliability and prolonging the service life of relief valves. Yet it still remains a major issue for industry.

Gaskets are included in the mechanical integrity section of the OSHA Process Safety Management regulation. These parts cost a miniscule fraction compared to the systems within which they are installed. Yet if they fail, the consequences can cause major catastrophes, and result in millions of dollars of damage, downtime, lost production and noncompliance penalties, not to mention injuries and loss of life. Add to these consequences the potential litigation and damage to the company’s reputation and the cost is virtually incalculable. It is imperative to ensure the right material of construction for the valves based on the temperature, material, pressure, and various potential factors in both the design and operation phases.

The use of appropriate gaskets, packing, bolts, valves, lubricants and welding rods must be verified in the field. Procedures are needed for verifying proper valve installation to ensure, among other things, uniform torque on flange bolts. Recent work at MKOPSC has investigated ways to predict leaks in valves using acoustic resonance. The technique relied on detecting shifts in specific resonant frequencies of the flange/gasket/bolt/piping assembly. Interpretation of the resonant frequency shifts can be used to predict when a flange connection will loosen to a point that allows leakage to occur.

MKOPSC also conducts extensive research into corrosion mechanisms, factors influencing corrosion rates and corrosion detection – an issue of great concern to those responsible for piping and valve maintenance. MKOPSC has investigated the use of RFID corrosion smart-tags in pipelines to allow for easy detection of pipeline corrosion and is also perusing research to see if smart pigs can be equipped with new sensors designed to detect microbiologically induced corrosion (MIC) in piping – a problem that’s often difficult to identify and address.

Utilizing Resources

With its goal to produce engineers and practitioners trained in process safety and provide an independent process safety resource for academia, government, and the world, MKOPSC invites members of the valve and end-user industries to utilize the experts and research at the center, which provides a neutral forum to discuss difficult issues related to process safety.

The center also serves as an information resource base for process safety, acting as a library and software laboratory. It provides consultation services for small and medium enterprises, government agencies, institutions, local emergency planning committees and others agencies. Independent accident analysis services are also available to industry and government agencies, particularly for accidents suggesting new or complex phenomena.

Dr. M. Sam Mannan is Regents Professor at Texas A&M University and the Director of the Mary Kay O’Connor Process Safety Center (MKOPSC).

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