A Matter of Convenience that Poses Risk

A pipe rack is the main artery of a process unit, plant layout expert Ed Bausbacher explains. Pipe racks carry process and utility piping, plus instrument controls running through cable trays and any equipment mounted above these.

That same definition applies to pipe alleys, pipe chases, pipe transoms and, in some cases, clusters of piping running underground. Thankfully, said Chevron Richmond, California, battalion chief Grant Tokiwa, you don’t find the underground version much anymore.

“We had underground pipe all over the place,” the 31-year Chevron veteran said. “Now we build them all above ground. You can see where it is leaking without digging the whole thing up.”

Different products and raw materials travel from one point in a refinery to another via piping. As a simple matter of organization, these pipes – ranging from one-inch to 30-inches in diameter – run along established pathways cleared between the machinery and storage tanks.

“Otherwise, they would be spread all over the place,” Tokiwa said. “How would you be able to get around?”

The downside of this necessity is the consolidation of potential risk. Volatile hydrocarbons travel next to caustics which travel next to flammable gases and so on. If one pipe is compromised, neighboring pipes quickly become vulnerable.

The pipe rack project at the Texas A&M Engineering Extension Service’s Brayton Fire Training Field involves an elevated platform situated above a flammable liquid containment area. Kris Simmons with Chevron’s Salt Lake City refinery served as instructor for project during Chevron’s recent training school at TEEX.

“You have a spill fire burning in the pit that can become a fuel-in-depth fire depending on how long you let the fuel run,” Simmons said. “A hose team has to work its way up the stairs to the platform to capture the valve controlling the fuel dumping into the pit. There is also a pump seal simulation to deal with.”

First foam is applied to the pit to control the spill fire. Packing a fully charged line, the five-person team works its way up the stairs. Water from the ground is used to control any fuel that continues to fall into the containment, trying not to disrupt the foam blanket.

“If somebody bumps that hanging line dropping fuel into the pit and it starts whipping around it can ruin the foam blanket,” Simmons said. “If the fuel dripping off the pump above is not captured, it can disrupt the blanket too.”

Tonnie Hopson, an assistant fire chief at Chevron’s Pascagoula, Mississippi, refinery, served as incident commander of the most recent Chevron fire school in March. He said gradual corrosion is the chief reason for pipe rack fires.

 “Some refineries have real salty water nearby, which means external corrosion” Hopson said. “If it’s a real hot pipe you could have corrosion between the pipe and the insulation that doesn’t expose itself until you have a leak.

As for internal issues, the life span of refinery piping is carefully calculated based on the accelerated corrosion resulting from some processes rather than others.

“All of that data is factored into and determines the frequency that piping is replaced,” Hopson said.

As a backup to the metallurgical timetable, ultrasonic technology allows non-intrusive – and non-destructive – monitoring of piping for corrosion, Tokiwa said.

“Our standard is that we can’t go below what we call ‘T-min,” which is the minimum thickness of the pipe,” he said. “If we have carbon steel pipe or some different material it is important to know what a particular product is going to do to it. You might have an acid reaction or sulfidation.”

Even vibration can eventually degrade the pipe to the point it ruptures. If the resulting spill ignites, the fire brigade goes to work.

Two types of fires result from pipe rack ruptures – spill or pool fires where the product gathered on the ground ignites or three-dimensional fires in which product burns as it falls from the pipe. Often both types occur simultaneously, dictating different extinguishing techniques for each.

Spill fires require foam. A foam blanket creates a vapor barrier separating the fuel from the oxygen needed for ignition. However, foam application to a three-dimensional fire is impossible. Also, using water to control the three-dimensional fire can potentially disrupt the foam blanket beneath it and reignite the spill fire.

“Dry chem, obviously, breaks the chemical chain, while water is for cooling and foam creates a vapor barrier,” Tokiwa said. “You use which ever is appropriate. You may have to use all three.”

Fortunately, some limiting factors come into play. If a massive pipeline ruptures, the above-ground emergency pipeline shut-off valve may be miles away. The fuel left in the pipeline after the valve is closed could burn for hours.

Isolation points in refinery piping are much closer at hand, making it much easier to shut down the flow of flammable products, Tokiwa said. Also, the long lengths of piping are joined by welding rather than flanges.

“The integrity of the pipe should be good for long runs,” Tokiwa said. “It’s only when you have flanges that you usually have leaks and problems.”

But one threat can compromise that neighboring piping – direct flame impingement. Pressurized product projecting a flame can ignite other lines carrying vastly different products.

Dry chemical is usually the recommended weapon in a pressurized three-dimensional fire. But handheld extinguishers lack the knockdown power to deal with these situations, Hopson said.

“Dry chemical is only going to give you about 10 to 15 minutes service time, so you’re only using it against intermittent fires – keeping small fires from becoming big fires,” he said.

What’s the solution? Hopson recommends using water to corral the spill fire to a location where it can accumulate, then apply the foam blanket to smother it. If your problem is a three-dimensional fire, the best option is to use water to capture the flame, then isolate the valve necessary to drain the system.

The exception to this advice is flammable gas. Blowing out the flame completely only allows the gas to accumulate in dangerous amounts. If it reaches a new ignition source is located, that gas can flash to life with almost explosive impact.

Regardless of what fuel is involved, the two words to keep in mind regarding pipe rack fires are control and isolation, Hopson said.

“If you have a fire in that area you want to make sure you isolate it quickly,” Hopson said. “You don’t want to expose everything in the pipe rack.”