The business manager for an asset management solutions (AMS) firm in the Middle East faced a big task. He had been asked to execute a major project for an oil and gas producer and wanted to have his questions answered on remaining rotating equipment life at existing client sites. The managers charge was to analyze large oil and gas plants that had been operating for far more than 25 years, although they were originally designed for 20 to 25 years only.
The aim of his AMS firm was to secure the future of the clients assets for another 20 years. The AMS manager had to determine what the client needed to do to stay in business for another 20 years without undue risk of production loss and without jeopardizing the high level of safety the company had achieved for its human and physical assets.
Before meeting with the manager and his staff, we had to set the stage for a productive week of meetings. Once we agreed that his firms charter was to quantify the remaining life of the clients turbines, compressors, pump and other equipment, the deliverables for a reliability consultant had to be delineated. The consultant defined his work effort to explaining key parameters and spelling out what the formula or approach would be for calculating the remaining life of each rotating machine.
Plant data are the key ingredients.
We believe that the key ingredients of any useful endeavor when determining the remaining life of machinery is hidden in the client plants own past failure history. Where such history exists and the root causes for the failures have been analyzed, authoritative answers on remaining life are possible. Conversely, when these data are lacking, applicable data from others would have to be substituted.
Regarding stationary equipment and piping, corrosion data should be available from coupons or from nondestructive testing readings. If no such test data are available from a particular facility, the AMS firm was advised to use third-party surveys and look at corrosion rates experienced in comparable industries and under comparable or scaleable conditions. This effort takes time and money.
Because our specialty is rotating machinery, we wanted to look first at process pumps. In the HPI, these simple machines suffer many thousands of unexplained repeat failures every year. We outlined to the AMS to focus on the pumps, audit the plants own failure history and past repair data first. To the maximum extent possible, plant data and pump configurations must be compared against upgrade measures taken by successful best-of-class organizations. Advanced lube application strategies are used by best-of-class facilities. These strategies must enter into the comparison, as will the extension of oil-replacement intervals made possible by better lubricants and superior bearing housing protection measures.
Mechanical seal life must be assessed and compared against best-available sealing technologies. This requires a liaison with the most competent mechanical seal suppliers. It requires the seal suppliers active cooperation and divulgence of what some claim (without real good justification) to represent proprietary information. For instance, the extent to which superior dual-sealing technology is of value must be determined on a service-by-service or even pump-by-pump basis.
In like fashion, the extent to which superior bearings (ceramic hybrids) would lengthen pump life or avoid bearing failures must be determined on a pump-by-pump basis. Lubricant application and standby bearing preservation are especially important in humid coastal and tropical environments, as well as in desert climates. Oil-mist lubrication extends the life of general-purpose machinery, and the AMS should consider it.
Piping and foundations affect remaining life.
Then there is the issue of piping for all machinery types. Just as residential sidewalks and the walls of houses move and settle, pipe supports and equipment foundations will settle. The effect of such settling on pipe connections and equipment nozzles can be visualized and must certainly be considered. Examining the grout support under base plates will be quite revealing.
Whenever steam turbines are used, blade stresses and water quality at the client site must be compared to those in successful long-running installations elsewhere.1 This is a time-consuming endeavor that requires an investigators time; mere guessing will not suffice. Of course, if a comparable experience exists elsewhere, the investigative effort may take less time.
In the case of geared units, remaining gear life must be examined by calculating tooth loading (stresses on tooth face) and from temperature measurements. In all instances, synthetic lubes from experienced oil formulators will greatly extend gear life. The right oil additives are needed for life extensions. They drive maintenance cost and affect gear life; oil cleanliness ranks next on the investigators priority list. Certain warehouse spares (gears, electric motors, etc.) should be upgraded, if important. Upgrading spares is likely to speed up equipment recommissioning after an unanticipated future shutdown.
Reciprocating compressor upgrades.
Since 1980, reciprocating compressors have benefitted from upgraded piston-rod coatings, improved rod attachments, effective onstream monitoring, more efficient valves, superior cylinder lubricants, improved volume control and a host of other add-ons or modifications. They are mentioned here because they serve as a model for questions raised and answers sought.
The key to knowing about these improvements lies in keeping track of the materials and appurtenances that were originally provided by the equipment manufacturer and to then ask what would be included if such equipment were delivered today. Once that question is answered, a cost-justification calculation will indicate if upgrading is appropriate. Needless to say, if the asset owners do not know the details of their machine, then the answers are more difficult to generate. As usual, data are important; without data, proper asset management will prove elusive.
Compressors: All of the above are important!
For compressors, one looks at all of the above discussed equipment. Valve technology and piston velocity are important comparison-worthy parameters on reciprocating compressors. On-stream performance tracking and observation of prior sealing experience are important for centrifugal and axial compressors. This performance tracking and a review of the clients present sealing technology determine seal-system upgrade potential. Even the compressor-internal seal materials must be examined in detail (Fig. 1) and judgments made as to their failure potential. Couplings and the work procedures associated with attaching couplings to shafts should not be overlooked; neither should shaft alignment quality and philosophy. They all tell a lot about the remaining equipment life and failure risk.
| Fig. 1. A compressor abradable seal detail.2 |
Whether a facility ultimately receives guidance from an established expert or whether an AMS puts its trust in someone else with similar experience is of no consequence, so long as the expert working for the AMS:
1) Authoritatively spells out recommended measures
2) Thoroughly explains recommended upgrade steps
3) Identifies recommended vendors that should do the upgrading
4) Defines the deliverables that should be contractually agreed on between upgrade the provider and the client. HP
1 Bloch, H. P. and M. P. Singh, Steam Turbines: Design, Applications and Re-Rating, 2nd Ed., McGraw-Hill, New York, New York, 2009.
2 Quance, S., Using plastic seals to improve compressor performance, Turbomachinery International, January/February 1997.
|The author |
Heinz P. Bloch is Hydrocarbon Processings Reliability/Equipment Editor. A practicing consulting engineer with 50 years of applicable experience, he advises process plants worldwide on failure analysis, reliability improvement and maintenance cost-avoidance topics.