THIS MONTH'S PUZZLER
A fuel gas pipeline in a pipe trench went under a road bridge inside a factory. A flanged joint, fitted with a compressed asbestos fiber (caf) gasket, was located only 2.5 m from the roadway (Figure 1). According to the area classification code used by the company there was a Division 2 area for a radius of 3 m around a caf joint and road vehicles should not be allowed unrestricted access to Division 2 areas. The factory wanted to open the bridge to unrestricted traffic.
Consider a third option
Another alternative is to build a wall along the edge of the bridge in place of the handrail. This would increase the distance that vapor would have to travel, before it reached a source of ignition, to more than 3 m (Figure 2).
This is a good example of a general rule: When it is difficult to decide between two courses of action, look for a third one.
Trevor A Kletz, consultant
Use secondary containment with a sensor
My recommendation is to leave the gasket alone for the reasons mentioned by the operations department. I would add a jacket around the flange and a sensor to detect if there is any leakage. The jacket would provide a small amount of secondary containment but would also concentrate any vapors so that the leak can be detected more readily. The signal should be transmitted to the control room and to a traffic light located at the bridge that signaled if travel on the bridge was safe or not. Since the flange has not leaked to date is a good reason to leave it alone but it does not insure that a leak won't develop in the future.
Kenneth W. Russell, consultant
Gateway Services, Seabrook, Texas
Upgrade gasket to the right material
The CAF gasket should be replaced by a spiral wound gasket at any cost. CAF gaskets are not suitable for sour gas service. CAF gaskets can be used only for a temporary gas service. Though these gaskets form a tight connection, as compared to spiral wound gaskets, when serrations are damaged CAF is unsuitable because it becomes brittle on long standing. If it leaks it will be disastrous.
Regarding the road usage, it is advisable to enforce restricted entry. Only vehicles fitted with exhaust mufflers (flame proof) should be allowed access.
Xavier Cyprian Jerard, process trainer
Oman Refinery Company, Muscat, Oman
Properly dispose of the CAF gasket
The gasket may not develop a leak, but why play the odds? SAFETY FIRST! Replace the asbestos gasket with the spiral wound gasket. If the binding material is intact (not friable) remove it, clean and inspect flange surfaces, and dispose of the asbestos gasket according to regulations. If the gasket is friable it may be required to glove bag during removal by a supervised asbestos worker. Replace the studs and nuts with ferilium. Then do a wire wrap with injector cap nuts and valves attached. Inject sealant through the valves into the space between the wire wrap and the gasket. This will insure the flanges integrity and prevent a major spill in the off chance the gasket should fail. If the area is able to trap the gas in the event of a leak, a lower explosive limit (LEL) gas monitor should be installed with a warning signal if area gets above the LEL. This may seem a bit extreme, however all data are not available and more measures may be needed.
Johnnie Walker, maintenance foreman
Noveon Kalama, Inc., Kalama, Wash.
We cannot simply leave the gasket alone and ignore safety. We have safety rules for a reason and if some rules are ignored, you will never have any assurance that your plant and process is safe. You will only know the plant didn't blow up yesterday, but you can't be confident about tomorrow.
Also, once the gasket finally is removed, it has to be properly marked for disposal per applicable regulations. Asbestos doesn't just go to the trash can.
Rather than replacing the gasket, use one of the proprietary "gasket bands" that several vendors make. Some have the option with a grease zert to fill the flange gap with grease or other thixotropic material that would be pushed out under pressure. After applying this, a six-month visual inspection would tell if there was leakage from the pipe because the grease would be pushed out from under the flange seal. Provided the safety department, plant operators, and engineering personnel are all happy with the flange the classification of the area could be changed. The gasket replacement could then be deferred until a future "opportunity."
If the flange is under the bridge and it is a confined space, gas testing may also be required prior to entering under the roadway bridge; the safety department should be able to make this rule clear.
Chuck Stewart, sr. process engineer
BP America, Houston, TX
Which is the safest route?
We can shift the flange joint away from the road bridge, remove the existing flange joint, and make it a welded joint. This will require hot work to be done. But this is a one time job and it is the permanent solution. By doing this we will obey the codes and safety.
Ashok Dayma, lead engineer
Alstom Projects India Ltd. New Delhi , India
Replace the gasket
Personnel safety must take precedence over any inconvenience.
Kent McKean, senior automation technologist
UMA Engineering Ltd., Winnipeg, Manitoba
Replace the gasket; move on
The code is for guidance; not the law". Only airheads think along those lines.
Codes are for the health, welfare and safety of all. If we as engineers do not follow codes, then why have them in the first place? Codes were written from experiences and lessons learned from disasters which caused death, dismemberment, disability and loss of assets.
There can be no compromising of safety for any reason. Replace the gasket and move on.
Richard Young, P.E., I/C engineer
Advanced Process Systems Division, San Diego, Calif.
A fuel station for a 50-MW emergency generator uses Number 4 fuel oil. It is to be pumped 500-feet from two horizontal tanks. A final pressure of 80-psig is required at the generator. The plant is in Wisconsin. The fuel has a gross heat of combustion of 140,000 BTU/gallon, a viscosity of 3000 centistokes at -10oF, and 62.5 centistokes at 70oF; the specific gravity is 0.85 at 60oF. The specific heat is 0.5 BTU/lbs.-F. The lowest mean temperature is 9.5oF. The design temperature, set by the plant standard, is 20oF below the minimum mean. The engineering team is grappling with how to minimize capital costs, operating costs, and problems.