In part 1 of this article, we discussed that a rotating machine begins to diminish in life immediately upon its first use. Although this may be a “sad but true” reality, noting that pumps and rotating equipment become more and more maintenance dependent as they rack up hours of use, there is no need to hide from it. In fact, the better able managers of maintenance/operations are to maintain a machine as it runs the course of its life cycle, the more capable they will be to extend the machine’s life and the better prepared they will be to decide when replacement is necessary.
In this section, we will address some of the real world techniques for ensuring your machinery is achieving its peak life cycle potential. These include making use of a time for rework or discrepancies, improving installation quality, and, lastly, being better aware of your machine’s characteristics of operation. Also, we will provide questions you can use to assess your maintenance strategy in terms of man-hour, equipment, and resource efficiency.
USE A DISCREPANCY PERIOD
The current period for rework/discrepancies applies to both new and refurbished rotating machinery. Once a machine has been released to operations, the clock begins. Any mechanical interruption in the following seven days from start-up will be considered a discrepancy and reported as such. A mechanical review will be mandatory by the zone, operations, client mechanical, and contractor reliability personnel.
Too often, plant managers feel the pressure to build an immediate ROI on new or refurbished equipment and believe that hitting the ground running is the same thing as being efficient. However, better prepared managers understand that truly efficient operation extends over the life of the equipment. A brief pot-installation discrepancy period can prove invaluable over the life of a machine.
IMPROVING INSTALLATION QUALITY
The improvement of installation quality will only be driven by improved work scopes and quality documented work procedures which have been tested, reviewed and tested for accuracy up to 3 times before final approval. The time taken up-front to prepare and inform the employees will always produce a higher rate of efficiency on the back side of the project with outstanding client satisfaction. Standards for Excellence have been written to elevate the levels of performance, create a guide as to what is or is not quality craftsmanship and to identify needs for additional training.
Currently, the time required to perform all of the necessary machinery inspections and checks may or may not be performed consistently throughout the refinery. The focus may or may not be to get the machinery back in operation without regard for mechanical integrity or capability. Our goal is to train every mechanical unit to understand the “why” when dealing with mechanical rotating machinery to include cause and effect for the client.
The Mechanical Vibration Institutions state that “90 percent of all vibration is derived from unbalance and mis-alignment” in rotating machinery today. We are concentrating upon the number one issue, which has been the use or application of the VibrAline Laser equipment.
KEYS TO A SUCCESSFUL INSTALLATION
- Whenever possible, begin by following a client’s maintenance forms. For example, centrifugal pump installation and alignment checklists are widely available from various institute’s standards and guidelines publications.
- Mechanical run-out is the primary cause for vibration known as unbalance. The physical weight of a rotating machine must be precisely identical 360 degrees from the center of the shaft to the outer rim of the impeller blades to minimize the effect of speed/velocity of the rotating parts known as “the rotating element.”
- Any excess weight misapplied during the overhaul balance process or during the installation process will directly affect the start-up and subsequent run-time of the machinery (High vibration will cause the machinery to be shut down immediately).
- The mechanical personnel installing rotating machinery must be conversant in vibration terminology and trained to minimize run-out and unbalance issues in the field.
- Currently, we are revising the alignment parameters for establishing improved thermal growth targets. Our goal is to enable the work force with credible data to perform single alignments on machinery while cold for a lower level of heat exposure to our field personnel. We anticipate a higher quality of mechanical performance as the work environment improves. We are going to present the process to the client for their buy-in as we get better data for the machinery. The results of our effort will be measured through the vibration trends and analysis program. The cold start-up vibration of machinery will be high, but as the machinery warms to operating temperature, the vibration trends should decrease to the expected levels or standards we call “Excellent.” We are committed to reducing the number of times we work on a particular machine as process interruptions are costly.
- Machinery must be treated as an entire package or system, as the overhaul of half the assets does not make the package reliable or operationally worthy. Our mechanical personnel will require additional training to understand the relationship between all components whether driver or driven.
- Machinery that is installed the way it was removed does not sustain the expected life of the machinery as we are setting new life cycle targets daily. We must caution our personnel that machinery may require full upgrade to become capable of reaching full expected life. Machinery identified as out of API specification may be installed as instructed, but must be accompanied with a variance document.
- Machinery installation currently being signed off without running the machinery with maintenance present is strongly discouraged. We recommend that operations and maintenance be present for the initial start-up of all critical equipment. Also, we recommend that a mechanical specialist observe and record data concerning temperature, pressure, vibration, and so on for the period of at least one hour before turning the machine over to the client operations. The baseline statistics must be satisfactory to expect to achieve full expected life.
- All critical machinery should require the job sign-off by supervision or mechanical reliability prior to release to operations. A walk around by supervision or reliability should be required on every critical job.
Machinery saves may be performed with operations and maintenance working together during the first hour of a machine break-in period for any equipment that has recently been refurbished or newly purchased. The start-up of machinery without maintenance may lead to incidents and catastrophic mechanical failure causing the machinery to require full removal from the operating unit increasing cost.
Operations may not be aware of the particular characteristics of every pump in their process. Maintenance has the responsibility of informing the client of best practices for making the machinery reliable and fully functional to achieve the expected life. Maintenance is responsible for informing operations with the life cycle characteristics of the machinery to allow the client to better plan, budget and operate the system. We should agree as to the mechanical, operational, and financial goals necessary for the profit structure budgeted by management to become reality. Certain operational requirements may not be conducive to achieving expected life cycle values mechanically.
Operations control the life of rotating machinery once a machine has lived beyond the warranty cycle of six to twelve months with the exception of preventive maintenance. The monthly rotation of machinery from “A” shut down to “B” start-up has a particular risk. The risk during every start of a pump is the loss of suction flow known as a “low flow condition.” Charge pumps, in particular, may be adversely affected by “low flow” due to the suction flow needed to circulate, cool, and lubricate the high speed internal rotating parts during the critical phase of a start-up.
Mechanical wear or failure generally occurs in seconds from the point of start-up until the machine gets too hot internally and the material in the pump begins to transfer metal from the rotating surface to the stationary surface of the pump. We call this condition “a bad start” and life has been retracted from the full expected life cycle of the machinery. The machine may come online but sustain irreversible wear or the machine may lock down due to complete loss of clearances. Our facility has some units without flow control detection while other units have diagnostic computerized systems making bad starts more accessible to track.
EXPECT THE BEST, PREPARE FOR THE WORST
In general, it is far too common for so-called routine maintenance to be seen as just that and, therefore, to be taken for granted. However, the “routine” is a misnomer. Every work stoppage or equipment check is a new and unique opportunity to analyze, question, and ultimately improve the life cycle of critical equipment.
The key to making maintenance a valuable component of a plant’s working life and not a costly impediment is recognizing the value of expecting the best from your equipment. The “little things” that people are tempted to let slide until the next repair add up to an early end for rotating equipment. However, if management, operations, and maintenance all hold their machinery to high standards, then they can reap the benefits. ■
ABOUT THE AUTHOR
Steve Reynolds is the quality control manager for Texas Rotating Equipment, Inc. of Dayton, Texas, a leader in turbomachinery related products and services. He can be reached at 936.258.3090 or firstname.lastname@example.org. For more information, visit www.texasrotating.com.
MODERN PUMPING TODAY, June 2013
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