Archive | September, 1997

258

2:19 am
September 2, 1997
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Preventable Maintenance Costs More Than Suspected

Engineers reviewed more than 15,000 work orders in the quest to identify the extent of preventable maintenance for major corporations in North America.

The concept of preventable maintenance (“Focusing on Preventable Maintenance,” MT 10/95, pg 23) has matured into one of the most powerful factors used by HSB Reliability Technologies’ (HSBRT) engineers to drive the reliability improvement process and lead clients to manufacturing excellence.

As with most good ideas, the process has been enhanced with experience. In addition to improvements in the investigative process, significant progress has been made in the solutions arena. It is also clear that there is still room for improvement of the investigative process.

HSBRT engineers now review two more aspects of the extent of preventable maintenance. The accompanying pie charts, from a study of more than 1000 work orders in a large plant, depict preventable maintenance in three ways.

It is first expressed as a percentage of the total number of work orders reviewed. The next chart shows preventable maintenance as a percentage of total maintenance hours. The third chart depicts preventable maintenance costs as a percentage of total maintenance costs.

As a percentage of total work orders
The graph confirms the original assumption that reasonably preventable maintenance approximates half of the work accomplished in most organizations. In this case it was exactly 47 percent. In this plant, an overly simplistic conclusion would be that about $18 million of labor and material was wasted.

Number Of Work Orders

As a percentage of total hours worked
HSBRT engineers decided that it would be beneficial to carry the analysis one more step. When expressed in hours worked, preventable maintenance appears to be a larger piece of the pie, in this case, 63 percent. A possible conclusion is that the preventable work orders were more complex, or at least more time consuming.

Time Spent

As a percentage of expenditures
Using the findings of the previous exercise, we examined the preventable work orders on the basis of total maintenance expenditures to determine the nature of the materials component. The percentage climbed to 69 percent. It would be prudent to conclude that preventable maintenance is more costly in labor and materials. Theoretically, $26 million was wasted in the study plant instead of $18 million.

Maintenance Expenditures

HSBRT engineers are now working to capture the impact of preventable maintenance in dollars of lost opportunity, or profitability of a particular plant. This measure has proved to be somewhat more difficult to define. We will keep you posted on our progress.

We are also working on specific solutions in systems, procedures, processes, and practices to minimize the impact of preventable maintenance. We have found reliability-centered maintenance/solutions and root cause failure analysis to be effective tools in this venture.

Identifying and controlling preventable maintenance are critical activities for managers who are serious about improving reliability and reducing maintenance costs. That may well be the most important area of focus because of the leverage on cost and throughput. MT


Raymond J. Oliverson is executive vice president and general manager of HSB Reliability Technologies, Consulting Div., 800 Rockmead Dr., Kingwood, TX 77339; (281) 358-1477.

HSBRT engineers Greg Como and Harold Weimer contributed to the article. Continue Reading →

452

1:26 am
September 2, 1997
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Using Ultrasound To Inspect Steam Traps

Faulty steam traps waste energy, they contribute to pipe erosion when contaminants are allowed to pass downstream, and they can add to environmental pollution and negatively affect product quality.

Steam traps should be inspected routinely. Inspection frequency is often determined by application. For example, steam systems used only for facility heating may be inspected annually and systems that use steam as part of a manufacturing process may be inspected biannually or quarterly, depending on the impact of steam on the process.

Some steam trap users replace trap elements annually. This can be costly and ineffective because traps can fail or leak at any time. Conversely, many traps will work for years before the elements need to be replaced.

As with any predictive maintenance program, knowledge of the system is critical. Before inspection begins, a map or diagram of the location of all steam traps and valves in a facility should be available. All traps should be tagged, coded, and referenced on the diagram. In addition, trap type, size, manufacturer, and application should be noted.

In addition to inspections, data should be collected to provide historical information about the steam system. This is useful in spotting recurring problems and possible clues about trap misuse, and in recording costs and savings incurred. Commercial steam management software is available.

Inspection methods
Once the records are in order, various inspection methods should be considered. The most common are visual, acoustic stethoscope, temperature, and ultrasound.

Visual inspection is effective if test valves are installed on the traps. This method assumes that an inspector can recognize the difference between a steam leak and steam produced by the effect of condensate venting to the atmosphere. In addition, venting to atmosphere affects the parameters of the closed system.

Low-frequency acoustic listening devices can be useful. However, because these devices sense all types of sound in a steam system, isolating a leaking trap, especially in a manifold, can be confusing.

The two most commonly recommended inspection instruments for steam traps are portable infrared thermometers and ultrasonic testers. Many trap inspectors use temperature devices to provide a close estimation of pressures on valves, traps, and coil heaters. They are also useful for spotting conditions such as heat loss, insulation problems, overheating, overloads, and cooling failures. These instruments should be used with ultrasound because temperature readings alone can be misleading. The many variables in a steam system, such as backpressure, can make readings based on temperature alone unreliable.

Of all the methods, ultrasound is the most recommended and most reliable. Ultrasound is a shortwave, high-frequency signal that does not travel far from its source. By listening to the ultrasonic components of a working steam trap, a user can isolate the signal and easily identify operational sounds.

Ultrasonic testers translate high-frequency emissions generated from the mechanical and fluid flows of traps into the audible range where they are heard through headphones and seen as intensity levels on a meter. Some units have frequency tuning to filter out additional signals and to tune in to the sounds of steam and condensate.

Testing steam traps with ultrasound provides results in real time. It isolates the area being tested by eliminating confusing background noises. A user can quickly adjust to recognizing differences among various steam traps.

Listening to traps
Although there are a variety of traps, for purposes of inspection there are two main types: continuous flow and intermittent (on/off).

On/off traps have a basic hold-discharge-hold pattern. Typical of this type are inverted buckets, thermodynamic, and thermostatic (bellows and bimetallic) traps. Continuous-flow traps discharge condensate continuously. The most common are float and thermostatic traps.

Each type of trap has a unique sound pattern. Inspectors should listen to a number of traps to determine normal operation in a particular situation before proceeding with a survey. Generally, when a trap is checked with ultrasound, a continuous rushing sound indicates live steam passing through.

Inverted bucket traps normally fail in the open position because the trap loses its prime. This condition means a complete blow through, not a partial loss. The trap will no longer operate intermittently. Aside from a continuous rushing sound, another clue for steam blow through is the sound of the bucket clanging against the side of the trap. Leaking steam has a continuous, slight hissing sound. An early warning signal of potential leakage or blow through in this type of trap is linkage rattling, which indicates looseness that can lead to steam loss.

Thermodynamic traps work on the difference in dynamic response to velocity change in flow of compressible and incompressible fluids. As steam enters, static pressure above the disk forces the disk against the valve seat. The static pressure over a large area overcomes the high inlet pressure of the steam. As the steam starts to condense, the pressure against the disk lessens and the trap cycles. A good disk trap should cycle 4 to 10 times a minute.

A thermodynamic trap usually fails in the open position, allowing continuous blow through of steam. A trap operating in good condition will have a distinctive shutoff between discharges, but a leaking trap will never shut and will produce a slight hissing sound. A worn disk produces a very rapid rattling sound that has been described as motor boating or machine gunning. This condition allows steam to leak through and is a predictor of more severe problems.

Thermostatic traps (bellows and bimetallic) operate on a difference in temperature between condensate and steam. They build up condensate, so when the temperature of condensate drops to a certain level below saturation temperature, the trap opens. By backing up condensate, the trap tends to modulate open or closed depending on the load. These traps have a hold-discharge-hold pattern. They can take a long time before discharging when there is little condensate buildup. At times of high condensate, such as at startup, they will stay open continuously. Therefore, it is best not to test these traps during startup. When closed, these traps are silent; a slight hissing sound indicates leakage. Blow through has a high-amplitude rushing sound.

A bellows trap does not function properly if the bellows becomes compressed by water hammer. A leak prevents the balanced pressure action of these traps. When either condition occurs, the trap fails in its natural position, either open or closed. If the trap fails closed, condensate backs up and no sound is heard. If the trap fails open, continuous rushing of live steam is heard.

When exposed to heat from steam, bimetallic traps have plates that set and discharge as they cool in the presence of condensate. An improper set prevents the plates from closing completely and allows steam to pass through. It produces a constant rushing sound.

Float and thermostatic traps contain two elements: a ball float and a thermostat. When the trap is operating properly, the trap ball floats up and down on a bed of condensate that keeps the discharge valve open. A modulating sound of the discharging condensate will be heard. The trap normally fails in the closed position. A pinhole leak produced in the ball float will cause the float to be weighted down, or water hammer will collapse the ball float. Because the trap is totally closed, no sound is heard.

In addition, the thermostatic element in the float and thermostatic trap should be checked. If the trap is operating correctly, this element is usually quiet. If a rushing sound is heard, either steam or gas is blowing through the air vent and the vent has failed open. If the mechanical linkage loosens, it will affect the operation of the discharge valve and can lead to steam leakage. This condition is heard as a clanging, rattling sound. MT


Information provided by Alan S. Bandes, UE Systems, Inc., Elmsford, NY; (800) 223-1325; e-mail ue@worldnet.att.net. Continue Reading →

198

9:25 pm
September 1, 1997
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Harley-Davidson Revs Up Its Maintenance Savings

Harley-Davidson Motor Co. in Milwaukee, WI, is upgrading its buildings on Juneau Avenue. The first building was constructed in 1906 to house the company’s manufacturing operations. Now the original factory has grown to a 650,000 sq ft campus, most of which is on the National Register of Historic Places.

Harley-Davidson produces heavyweight motorcycles and a complete line of parts and accessories. Until 3 years ago, building and equipment maintenance was managed almost entirely on paper by the facility’s maintenance staff.

In addition, the company’s maintenance inventory had grown to about 10,000 parts valued at about $120,000. Most items were small parts, such as nuts, bolts, and pipes, and electrical components, such as gang boxes and fuses. All of them had to be tracked so that maintenance was never caught short.

“Everything ran fairly smoothly, but things did not always get done, because a piece of paper may have been misplaced,” says Andy Thorsen, acting maintenance manager for Harley-Davidson.

The facilities manager, along with the company’s information services group, decided to automate maintenance operations at headquarters using an IBM AS/400-based computerized maintenance management system (CMMS) already in one of the company’s manufacturing plants. “It just did not fit our needs,” says Thorsen. “It was geared more for a manufacturing facility than for a corporate headquarters with office buildings and labs.”

The maintenance staff decided on a more relevant set of criteria for the CMMS. First, the system had to be based on personal computers (PC). Second, it had to have the ability to create custom work orders. And the software application had to be based on a nonproprietary database.

After reviewing several CMMS applications, Harley-Davidson chose Datastream’s MP2 for DOS, upgrading to a Windows version a year and a half later. The multitasking system has several integrated modules that track and schedule maintenance tasks and resources. The modules cover maintenance areas such as equipment, labor, service and work order requests and management, preventive maintenance (PM), statistical predictive maintenance, inventory, and purchasing.

Implementation was gradual. First, details about the equipment at the facility were entered. Then about a year’s worth of paper-based work orders were entered into the system. This information provided a maintenance history for reports, existing maintenance work orders, and inventory. Next, the maintenance inventory was entered into the system. Along the way, the maintenance staff established cost centers and began to assign accounting codes to all equipment to identify the department for which work is done.

To handle work order requests, Harley-Davidson purchased a Work Request System module in early 1996 to replace its paper-based system. About 30 PC-based dedicated workstations are distributed across the complex. Work requests are entered into the system and then sent electronically to the maintenance department. The system collects basic information, such as the name and location of the person initiating the request, and a description of the work needed. Thorsen uploads the requests to the work order module, which generates and prints preventive, corrective, and predictive work orders. He can also create and print work request history reports by type of repair and reason for breakdown.

CMMS in action
The CMMS is used daily by 10 maintenance people covering six crafts: millwright, piping, machine repair, electrical, stationary engineering, and shipping. They use a workstation in the shop to enter work order information.

Harley-Davidson uses the PM Tasks module extensively, explains Thorsen. “Probably 80 percent of our machine repairman’s job is PMs, maybe 15 a week, ranging from one hour to a whole day per. About a year ago, we decided to put this all on the computer. That way, we can track costs, inventory, and tasks.”

Setting up PM tasks was not difficult, according to Thorsen. With an equipment description already in the system, Thorsen and the repairman only needed to enter a description for the PM task, including frequency and task instructions. Each month the department adds more PM tasks.

Work requests are scheduled on a priority system. “We have priorities one through five, where one is a safety item and five is whenever we get to it. Most of them fall in the two to four range,” Thorsen explains.

The Work Order module assigns and tracks all the PM tasks and new work order requests, scheduling resources as necessary. Normally, the system generates between 70 and 80 orders a week. To make servicing easier, Thorsen has set up the work orders so that all orders for a specific building are scheduled at the same time.

Harley-Davidson also implemented a module that includes an electronic catalog from W. W. Grainger, Inc., with more than 200,000 tools and parts for maintenance and other applications. Maintenance personnel can import data from the catalog directly into the system’s inventory and purchasing functions.

An Occupational Safety and Health Administration (OSHA) database includes OSHA regulation sections 1901 through 1910. Maintenance personnel can cut and paste information directly from that database into work orders.

A bar code module lets maintenance personnel enter data directly into the system. Data include personnel and part identification numbers, work order numbers, start and finish times, and other details to close out work orders. Bar coded maintenance documents can be printed, along with bar coded labels for inventory parts.

Regular maintenance saves money
Virtually all manual maintenance management has been eliminated. Paper-based work orders have been reduced by 95 percent. The maintenance staff is no longer swamped by paperwork, work orders are no longer misplaced, and maintenance calls are handled immediately.

In addition to standard reports on labor, equipment, inventory, and efficiency, customized reports can be produced, including a monthly report listing work orders by departmental accounting code. This feature lets the maintenance department know how much to bill which other departments. Routine tasks such as replacing light bulbs are not charged back to the departments, but the report shows those items too.

The system’s greatest benefit, according to Thorsen, is the capability to create, schedule, and track PM tasks for all kinds of equipment–and track the labor and materials costs associated with those tasks and new work orders. This information becomes the basis for the cost/benefit analysis required in the maintenance department’s repair-or-buy decisions.

Using the CMMS has allowed Thorsen to shift maintenance labor to more productive tasks. “We’ve saved a lot of money on maintenance costs and parts by doing PM tasks–just oiling and checking belts, tightening belts on conveyors, tightening rollers, and doing work like that on schedule,” concludes Thorsen.

“We have become more anticipatory, more foresighted instead of reactionary. Before, we’d wait until something was down; then we’d fix it. Now, we see if we can make it not go down in the first place. It’s like that with all our machinery, and it’s been very successful.” MT


Information supplied by Datastream Systems, Inc., Greenville, SC; (800) 955-6775. Continue Reading →

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