Often, plant turnarounds end with the maintenance work over budget. Budget excesses can arise from unforeseen work, extended shut-down length, and expediting charges. Unexpected costs arise because of extra work that was not planned before the shutdown. Unplanned work increases costs and reduces profits. In a climate of relentless cost cutting, reducing unplanned work, and maintenance exposure to unplanned work, is an important step in keeping plant costs under control.
Business (cost) exposure in maintenance work arises from two areas. First, the expected work may have been planned at a lower cost than actually spent. Second, 'surprise' items are found after the equipment is opened. Cost control can work on either area. In the first area, costs must be properly estimated. In the second area, maintenance items should be identified in advance.
Most efforts in the literature on improving maintenance costs and maintenance control emphasize reducing the cost of the identified work and on estimating its cost correctly. While useful, this step is not as important as knowing in advance what you need to fix. We will concentrate on identifying problems in advance.
Once a work item has been identified, the exposure in the maintenance budget to cost overruns is a function of how well the repair has been defined, procurement for goods and services, market conditions, and estimating procedures. With good control in these areas costs can usually be maintained with 20% of projected values. In comparison, missing an item completely has a much larger affect. First, you miss the cost by 100% on the base price. Second, procurement must be expedited; at costs that are often 1000% or more of standard procurement rates. Third, and worst, either by the nature of the work itself or its impact on other activities, the entire turnaround can be delayed.
Defining maintenance requirements is the responsibility of the entire operations staff. This includes support engineers as well as the unit operators. Simple methods are available to identify problems in advance with most process equipment. For our examples, we will concentrate on towers (distillation, absorption, extraction), heat exchangers, and drums. Similar simple methods are available for other process equipment.
Getting experienced process engineers involved in equipment and unit surveys is one key element. One type of survey is to take pressure and temperature profiles across the process equipment. Another type is whole unit test runs. Test runs immediately after startup set a base line of unit performance. Follow-up test runs during the unit operation gather data for comparisons. Comparing test run results over time is a key to identifying equipment performance problems. Identifying the cause of equipment performance failures is the key to proper definition of maintenance requirements.
Examples show different types of field data that can identify some common equipment problems. The examples concentrate on how engineers using basic, straightforward principles and applied thought can identify major problems. Thousands of pages of examples could be used to illustrate different approaches. The examples are only a taste of what can be done. The engineer's field experience, ability to grasp the basics, and imagination in applying them are the only limit.
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