True reliability professionals are known to be hard-workingand knowledgeable. But, they sometimes have difficulty quantifying the value of their efforts in monetary terms. They don't always speak the accountants' language and seem reluctant to calculate return on investment. As this four-part series will show, it doesn't have to be that way. Most managers will cheerfully listen to and consider a few written sentences and a hand calculation showing simple payback. Let us alert you to a sampling of a few machinery-related reliability enhancements with calculated—and often proven—paybacks of 10:1 and more over the life of the equipment. Each of these case histories is thoroughly experience based and easy to implement, even on a tight budget. The different installments of this series address aspects of lube life extension, advanced lubricant application, rolling element bearing selection, energy conservation and cost-effective means to reduce valve failures in reciprocating compressors.
Synthetic lubes for rolling element bearings
Equipment reliability is obviously influenced by the quality of bearing lubrication. For good reasons, then, the pursuit of quality lubrication has focused on application method, lube quantity, selecting the appropriate oil type and viscosity, properly storing and handling the lubricant, attending to bearing housing contamination issues and implementing appropriate oil change intervals. (Ref. 1) It makes sense to summarize good lubrication practices as: choosing the right oil, taking proper care of it and changing it on time. Yet, while good lubrication practices lead to improved equipment reliability by maximizing the performance of the oil selected, there are limitations. This is because in and of themselves good practices cannot impart lubricating properties that the oil perhaps never possessed in the first place. Thus, at issue is the definition of the right oil, or appropriate oil type. Putting it another way, improvements in lubricant quality can only be achieved by selecting and utilizing oils with superior lubricating properties.
High film strength synthetic lubricants
Synthetic lubricants offer the most obvious path for improvement. Even among prominent synthetic lubricants, however, oil performance can vary greatly based on the amounts and types of additives in the oil. At least one company combines synthetic base oils with advanced additive chemistry so as to realize greater film strength.Numerous incidents have been documented where advanced lubrication technology has significantly improved pump reliability (Ref. 2). While we will limit our coverage to just four examples in this topic category, formulators and marketers of synthetic lubes will be ready and able to furnish more data.
Hot oil pump experience…
One chemical plant began to experience bearing failures in its 500 F hot oil pumps within 90 days of plant startup, despite the fact that the pumps were already being lubricated by a premium brand of synthetic oil. Root cause analysis determined that failures occurred because high temperatures had caused the synthetic oil to oxidize. All pumps underwent immediate oil changes with nine of the 18 hot oil pumps being converted to a superior film strength synthetic oil. Again, all of the pumps using the original oil required an oil change within 90 days. The superior film strength oil, however, proved to be a lubricant upgrade that eliminated the bearing failures and enabled annual oil intervals to be established for all of the hot oil pumps.
A four-fold extension of oil exchange intervals results in a 75% reduction of oil usage after changing over to the high-grade synthetic lubricant. The reduction in consumption makes up for the fact that the synthetic lube costs four times as much as the mineral oil used before. Tangible savings accrue due to 200 man-hours of maintenance labor being reduced to only 50 man-hours. At $50 per man-hour, yearly savings are $7,500. Although intuitively evident to exist, no additional credit was taken for the imputed value of reduced failure risk with superior film strength synthetic lubricants. Nor was credit taken for Cv, the gain due to pro-active use of the re-assigned workforce. In other words, the value of pro-actively employing 150 man-hours of freed-up manpower must logically be assumed to exceed $7,500—or else the plant would not make any profit.
Critical API pump experience…
Another refinery was experiencing high vibrations and an audible noise from the inboard bearing of a critical, non-spared pump in one of its process units. The refinery was able to avoid a unit shutdown by draining the oil while the pump was operating and replacing the quart (~ one liter) of ISO 32 synthetic oil already in the pump with a superior film strength ISO Grade 32 synthetic. The high vibrations disappeared (see Ref.1 for a technical explanation), as did the audible noise, and it was decided repairs to the pump were no longer necessary. The value of an avoided repair was estimated as $2,500 for a bearing change only, $13,000 for bearings and seals and $54,000 for a complete pump overhaul.Additionally, unit downtime would have amounted to $140,000 per day.
Whatever the differential cost of a quart (or liter) of high film strength synthetic, perhaps three or four dollars in 2006, it is simply insignificant compared to the value of a failure incident on critical, non-spared refinery pumps. Critically important and hot service pumps should, therefore, be lubricated with high film strength synthetic oils.
Hot water pump experience…
For years, a U.S.Gulf Coast chemical company had averaged two to three bearing failures every six weeks in its 30 hot water pumps. These pumps were lubricated by oil mist, using a premium brand synthetic oil. In an effort to improve pump reliability, the lubricant was changed to a greater film strength synthetic lube. In the three years since, only one pump failure has been reported and it was not lubrication related. While this may sound like a purely anecdotal report, we are including it here because it is quite representative of well over 100 similar case histories that users have shared and reported over the past decade or so.
Disc filter shower and bark booster pumps experience…
A Canadian paper company experienced frequent difficulty with two 3,600 rpm pumps. These difficulties have been eliminated by changing the R&O mineral oil lubricant to a synthetic with greater film strength. As is so often the case, the latter have the ability to avoid metal-to-metal contact and the resulting temperature reductions tell the story:
Temperature Readings, Disc Filter Shower Pump
|Inboard Bearing||170 F||130 F|
|Outboard Bearing||185 F||160 F|
Temperature Readings, Bark Booster Pump
|Inboard Bearing||180 F||130 F|
|Outboard Bearing||170 F||114 F|
With shower pump outages causing plant downtime, a pump repair incident cost the facility $35,600. A single instance of repair avoidance may make up for the incremental cost of supplying high film strength synthetics to an entire paper mill.
Similar temperature reductions were experienced on bark booster pumps. However, each booster pump failure was reported to cost only $3,600 because it did not cause a production stoppage.
These examples are but a few of the hundreds where lube selection was responsible for significant improvements in pump reliability. High bearing temperatures and vibration excursions related to elevated surface roughness of bearing metals can very often be cured by selecting and installing superior performing lubricants. Especially in problem pumps, upgrading to high-strength lubricants can improve equipment reliability in a manner unattainable by any other means.
Indeed, since oil changes are often feasible while pumps are on-line and running, using superior film strength synthetic lubricants often results in immediate payback. Virtually every cost justification calculation indicates unusually large benefits for employing these lubes on problem pumps and 10:1 payback in a single year is rather the norm.
Recip compressor valve experience…
A pair of reciprocating air compressors in a chemical plant were in alternating service (one week continuously on, then off), using an ISO 150 mineral oil (Ref. 3). Carbon deposits on discharge valves caused such operating problems that the machines required maintenance every three months.
In an operating test, one compressor was switched to an ISO Grade 100 diester synthetic lubricant. After more than six months, discharge valves on this compressor were substantially cleaner than they were on the unit that used mineral oil for four months.
The diester synthetic allowed compressor maintenance intervals to be doubled from three months to six, at a very significant saving in labor and materials. The comparison photos (Fig. 1 and Fig. 2) tell the story, as does the cost justification calculation in Table I.
As shown in Table I, the incremental amount of $320 for the superior lubricant saved the plant $10,130—which yields a payback ratio in excess of 30:1. It should be pointed out that in the overwhelming majority of gas services, similar advantages accrue when using the diester synthetic as a cylinder lubricant.However, just as not all process gases are compatible with mineral oils, so not all gases are compatible with every type of synthetic lubricant that is being marketed today.A reliability-focused user will keep this in mind, but will not hesitate to check into the applicability of modern cylinder lubricants.
In the reciprocating compressor example referenced here, shutting down one of the two compressors did not curtail plant production. Experience shows, however, that in process plants with "non-spared" reciprocating compressors, an outage event would interrupt plant production. In those instances, payback for using diester synthetic lubricants has often exceeded a 10:1 ratio each year.
In Part II of this four-part series, the topic of pre-grouted baseplates will be covered. LMT