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Process Safety Management

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Avoid Safety Pitfalls During Plant Expansion and Modification

| By Bill Wasilewski, Day & Zimmermann


Follow this guidance to minimize risk when adding or modifying plant equipment

In 2015, construction in the chemical process industries (CPI) soared. Capital spending surged 18.4% and 255 new chemical production projects were announced, according to the American Chemistry Council (ACC) [1]. Since that year, the market has backtracked due, in part, to falling natural gas prices. However, capital spending still increased by 6% in 2017 according to the ACC [2]. That means some projects are moving forward. As CPI plant operators consider how to proceed in the coming years, many may opt to increase capacity or yield, or to add new product streams through the use of more modest expansions or upgrades to existing plants, rather than new construction. Plant expansions and renovations can be an effective way to increase capacity without incurring the higher costs associated with grassroots construction.

To make such site improvements as successful and cost-effective as possible, they must be executed carefully, with special attention paid to process engineering and plant safety considerations. Even seemingly minor upgrades can create safety issues if not executed properly. Meanwhile, larger projects may require significant changes to plant layouts and complex engineering adjustments that can make them as challenging from a safety standpoint as greenfield construction.

One of the most famous and unfortunate examples of a plant modification leading to a safety disaster happened in 1974 at a chemical processing plant in Flixborough, U.K. Twenty-eight workers were killed and 36 others were injured in an explosion that was traced back to a modification made two months prior. A leak in one of the plant’s reactors had been discovered. To avoid a plant shutdown, engineers installed a temporary pipe intended to bypass the leaking reactor until it was repaired.

A later investigation found that both the pipe that was used and the installation process were substandard. The project was hastily executed without proper consideration for the overall engineering implications. The incident sent shockwaves through the international chemical engineering community, and it led to significant regulatory reforms across Europe, and broader initiatives around the world, focused on improving process safety.

Some of the underlying factors that led to the Flixborough disaster are still a risk today. There will always be pressures on plants to remain efficient and profitable. Communication between contractors and plant operators must always be managed carefully. Despite the numerous process improvements that have been made in the 40 years since this disaster, human error is possible in any complex process.

The engineering upgrade that led to the Flixborough disaster was not a massive expansion of a plant with many moving parts. Rather, the project involved just a single, specific change to one aspect of operations. Today, larger, more complex modifications carry even more risks. To mitigate risk and reduce the incidence of serious hazards, it is critical to examine and understand some of the most common pitfalls that can lead to major accidents at chemical process plants.

Key systems

While managing risk in a plant is complex and involves many moving parts, the equipment systems discussed below are key areas that should be considered most carefully during expansion and modification projects.

Relief-valve systems. Relief valves are essential to maintaining plant safety and avoiding potentially devastating accidents. Unfortunately, proper implementation, and the safe use and functionality of safety valves are sometimes misunderstood or overlooked by plant operators.

When plants expand, the additional throughput capacity that must be handled by the relief valves in the facility usually pushes the limits of the original design. To compensate, plant operators may need to change out old valves for new ones. In some cases, a valve change is not enough. If a new valve is installed within the same inlet or outlet piping size and configuration, it can create a bottleneck around the new device. Additionally, the relief-collection header system may be inadequate for the new higher pressure levels likely to be encountered. A thorough review of the entire plant is necessary to determine exactly what needs to be replaced and how it should be done.

Some firms may overlook specific relief-valve systems that are not in the immediate vicinity of the new construction. In reality, relief-valve systems in one area of a plant may be impacted by a new piece of equipment hundreds of yards away. If any single relief valve is not adequate or does not meet proper specifications it could lead to a complete disaster.

On occasion, plant operators also overestimate the capabilities of a particular piece of equipment. For instance, a boiler might be capable of handling an increased amount of pressure as the result of a new project. But there may be piping or valves attached to that boiler that are not able to handle the increased pressure.

A complete audit of relief-valve systems should be a part of any plant modification, expansion or update. It is critical that plant operators partner with contractors to ensure that no part of this process is overlooked or rushed. Problems with relief valves can be one of the most devastating and dangerous problems a chemical process plant can face.

Piping and pipe racks. In addition to relief valves, piping should be thoroughly assessed and reviewed during any type of plant modification or expansion. In a mature plant, pipe racks often have little or no space for expansion. These limitations should be identified early in the planning process so that there are no unexpected costs for rack expansions. It’s also not uncommon during modifications to discover that pipe racks are overloaded beyond their design rating. This poses serious safety risks that could lead to potential explosions. That’s why it is always more prudent to add additional pipes to increase flow.

Another potential hazard is the presence of “dead-leg” pipes. These pipes are disconnected from the plant’s process and are left behind from previous maintenance work or plant fixes. Dead-leg pipes take up unnecessary space on a pipe rack, but more importantly, they pose a safety risk. Stagnant liquids left in dead-leg pipes can lead to pipe corrosion or rupture if the liquid freezes.

Many plants have dead-leg pipes that have not been part of the active process for years. As dead legs increase in number, the risk to the plant multiplies with them. When dealing with hazardous chemicals, small amounts of pooling liquid in dead legs can lead to major ruptures or leaks. Plants should have regular programs in place to inspect piping. While there are scenarios where it may make sense for a dead-leg to remain, unnecessary dead-legs should be removed during plant expansions and modifications.

If there is a change in plant processes during construction, it could require further changes in the piping. For instance, new chemicals may require different piping materials. A process change may also require new gaskets or elastomers.

Piping and pipe racks are everywhere in chemical process plants. It only takes a problem arising in one of those pipes for a safety incident to occur. That’s why a thorough inspection of pipes and pipe racks is necessary as part of any expansion or modification.

Access and confined-space issues. Adding new pieces of equipment or building new areas onto an existing plant can have a significant impact on plant layout. Large vessels installed to increase output, can also create new hazards. Placement of new equipment may create unsafe confined spaces or limit access to critical infrastructure. While a certain number of confined spaces in a CPI plant may be unavoidable, designs should try to minimize them as much as possible.

During construction, there are often temporary installations that restrict access to certain areas of the plant. Any additional equipment that is necessary to complete a project — such as scaffolding — should be placed carefully to ensure that it does not restrict key access areas.

Even under the best of circumstances, confined spaces are extremely dangerous. Potential safety hazards associated with confined spaces include the ignition of flammable liquids or gases, asphyxiation and exposure to hazardous chemicals [ 3].

The U.S. Occupational Safety and Health Admin. (OSHA) has strict standards for confined-space safety. Workers are not allowed to enter confined spaces unless they have proper training and specific equipment. But despite these safety standards, accidents happen with troubling regularity. The U.S. Bureau of Labor Statistics estimates that on average there are 92 fatal injuries in confined spaces every year.

Appropriate labeling (especially for chemicals and piping). Having proper equipment labeling and documentation is the easiest and the least costly way to improve safety. It is also one of the most overlooked. According to OSHA, hazard communication is the second-most-cited safety violation for businesses, behind fall protection [ 4]. Last year, OSHA began requiring all chemical-hazard labels to adhere to the Globally Harmonized System established by the United Nations. This system was designed to be universally understandable.

While OSHA has made great strides in the area of chemical labeling, it does not mandate every type of labeling in a plant. Particularly when it comes to piping, the responsibility for labeling falls solely on the plant operator. While there are no specific OSHA requirements for pipe labeling, OSHA does recommend the ANSI/ASME A13.1 pipe-marking standard [ 5].

Even though OSHA does not have strict requirements, plants should follow a prudent approach — those that don’t label pipes do so at their own peril. New construction ofen changes equipment processes and therefore labels should always be updated to reflect changes, so there is no confusion.


Closing thoughts

When a plant adds new features, installs new capital-intensive equipment or expands production capacity, it is an exciting time for plant operators, workers and the community. It means increased revenue for the company, jobs for workers, and economic development for local communities. While plant operators want to be efficient with their capital spending, many of the potential pitfalls discussed here are not costly to investigate and correct. Plant operators should find engineering, design and construction partners that are committed to thoroughly evaluating all of these areas to ensure that their investments are protected and are not put in peril. n



07EM~Wasilewski_Bill-250x350Bill “Waz” Wasilewski is president of process and industrial for Day & Zimmermann (Patewood 5, 80 International Dr., Suite 100, Greenville, S.C.; Email: He is responsible for oversight of the company’s chemical, advanced manufacturing, petroleum refining, and food and beverage customers. He has more than 30 years of experience at large engineering and construction firms.




1. Year-End 2015 Chemical Industry Situation and Outlook, American Chemistry Council,

2. Outlook: U.S. Manufacturing Turns Corner, Rides Upswing of Global Economies; Chemical Industry Growth Rate Surpasses 20-Year Average as Industry Rebounds from Historic Hurricanes, American Chemistry Council,

3. Meyers, Kelly, 7 Safety Incidents You Should Look Out For in the Oil & Gas Industry, Blackline Safety,

4. Top Ten Most Frequently Cited Standards, Occupational Safety and Health Administration,

5. Graphic Products Editorial Staff, OSHA Pipe Labeling Requirements, Graphic Products,