The Power of Prints

The Power of Prints

Good maintenance depends on good drawings. Maintenance is an information-driven undertaking. The four cornerstones of the information “building” are drawings, equipment data, test measurements, and training. This information building is shaky if drawings aren’t what they should be, and the maintenance function will suffer as a result. How long does it take you to locate the energy source for a given

Good maintenance depends on good drawings.

Maintenance is an information-driven undertaking. The four cornerstones of the information “building” are drawings, equipment data, test measurements, and training. This information building is shaky if drawings aren’t what they should be, and the maintenance function will suffer as a result.

How long does it take you to locate the energy source for a given piece of equipment? Once you locate it, how sure are you that locking it out will make that equipment safe to work on? What will de-energizing that equipment do to the production process? The answers to these questions are always better answered when you have good drawings than when you don’t. Let’s look at three fictional scenarios to illustrate that concept, and then consider ways to maintain good drawings in your facility. Keep in mind that today many people maintain many drawings electronically—sometimes embedded in control systems—but you also must often work with drawings that aren’t strictly electrical just so you can do your electrical work.

Lockout/tagout. Betty has to replace the motor on the rollup end (output) of a large extruder because insulation resistance tests show it’s going to fail soon. She can follow lockout/tagout procedures to de-energize the motor quite easily—all she has to do is shut off the disconnect that’s within sight of the motor. But that doesn’t mean she’ll be able to safely work on that motor. The extruder has heating barrels and a feed motor, plus the whole system has various alarms and 120V switches. If she leaves the extruder in service, she could inadvertently damage a live 120V lead to a switch or suffer injury from some process action, so she must de-energize more than just that one motor.

In the continuous process environment, electrical workers have traditionally used piping and installation diagrams (P&IDs) to see the process sequence and inter-relation of vessels, valves, mixers, and other major equipment. Today you can usually call up similar information in the PLC or DCS that controls the process. So in this case, Betty can look on the motor for its equipment ID and search for it in the PLC interface. In seconds she’ll have a drawing that shows her what equipment her motor ties into. This search will also reveal that she has to disable a “rollup stop” alarm that trips on loss of power to the motor. She can do this by “forcing” the output in the PLC. There are other alarms she’ll have to disable as well. Once she’s taken care of not giving false alarms to the operators, she’ll have to determine which devices to de-energize. By not de-energizing all of the barrel heaters, she can more quickly return the extruder to service.

This same scenario could apply in a variety of circumstances where the equipment is integral to a process. You must first understand the process, then understand the role of the equipment in that process, and then understand which equipment to de-energize and how to de-energize it. The more accurate your drawings are, the easier this is.

Upgrade a motor. In an extruder application like Betty’s, the motor is the right size for the application because the extruder is designed as a unit. But suppose you have a different application, such as a mixer. A recent product change means the same vessel now holds more viscous product and the impeller must rotate 25% faster. The increased viscosity means you need more torque, achievable with a gearbox. However, torque multiplication means a speed reduction, and this process requires more speed. The only solution is to use a larger motor and control the speed with a VFD. But if you’re replacing a 10-hp motor with a 50-hp motor, you’re going to go from a NEMA 1 to a NEMA 3 starter. Where’s the starter? And what about the breaker supplying this motor? You’re going to increase your current draw from about 15A to about 70A—will you exceed the wiring ampacity?

To upgrade this motor, you must do several things beyond just replacing the mounting hardware. You’ll need to go to the system drawings to find which bucket in which MCC feeds the existing motor, and you’ll need to see if that bucket can carry the additional 55A. If not, you’ll need to locate a bucket that can. Your drawings will tell you which circuits do what and will identify them by number. You’ll also need to locate the pullboxes for that conduit run. These should be on an installation diagram. If they aren’t, you’ll have to walk the plant and look for them.

Troubleshoot a nuisance trip. Suppose Betty gets calls that one breaker keeps tripping. How would she determine why it trips? The most effective way is to look at the drawings and identify the major loads. Then, using the drawings, she can determine certain things about those loads, such as the presence of overload units. Suppose she finds two phases are carrying excessive current. This would indicate a loss of phase in a motor, and the drawing would tell her which motors to look at and give her some basic information on each one. If she needed to isolate a ground fault, the drawings would tell her which connection points to investigate, which cables to test, and which loads to check. She would also know the breaker size, settings, and location without having to hunt for that information.

Maintaining drawings. Given the power of good drawings, why are bad drawings so prevalent? More importantly, what can you do about that in your facility? Eric Smart, a maintenance expert who has consulted at dozens of facilities, notes that the excuse for poor drawings is almost always the same and runs something like, “We’ve upgraded over the years, so our drawings are just out of date.” He also points out that even though contracts call for as-built drawings, few firms ever enforce them, so they don’t get good drawings to begin with. This creates a treadmill situation where losses in efficiency caused by outdated drawings prevent you from updating them or ensuring they’re good to begin with. Not all facilities encounter this problem, though. For example, nuclear power plants aren’t susceptible. The following steps are used by plants to reduce maintenance errors and increase efficiency.

Make updates quick, easy, and coordinated. One procedure involves marking up a drawing and sending it to a central place (plant engineering department) for approval. Once the central authority determines that the proposed change won’t conflict with other requirements, it issues an updated drawing that shows pending field changes. The change should then be made in the field to match the drawing. To get compliance, set up a system that requires minimum effort from field technicians.

Practice version control. ‘Pack ratting’ means someone will always have outdated drawings to work with. Storing drawings electronically in a central location and then printing date-stamped drawings on demand eliminates drawing obsolescence. A good system notifies you when a revision comes out.

Make access easy. Crews need access to the drawing system around the clock. Even if your facility doesn’t run around the clock, maintenance and construction operations take place on weekends and holidays. Plus, you want drawing access in case of emergency. One way to make this work is to have all drawings available on a central server. Whatever your system, make sure it doesn’t make people stash paper copies rather than go through the hassle of getting a new drawing. Many field service firms now provide wireless access to all documentation related to a customer. Construction firms are now using enterprise-wide project management software that ties all related documents to a given task. And plant maintenance technicians in some manufacturing plants have wireless access to all documentation related to a given equipment ID

Remember, good drawings are essential to doing good work in a cost-effective fashion. If you don’t have a system in place now to ensure you’ll benefit from the power of good drawings, you have an investment choice to make. Are you willing to lose the revenue that results from stretching equipment downtimes far longer than they would be if you had good drawings? If not, your choice is clear.

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