Testing

Introduction

The word test is quite broad in its definition, and many of the inspection steps in the course of the compressor manufacturing cycle can appropriately be called tests. An example would be the material tests. The API mechanical equipment standards, however, attempt to narrow the test definition. This chapter will discuss testing within these narrowed definitions. The first test defined in most API mechanical equipment standards is the hydrostatic test, and it will, therefore, be the first test covered in the chapter.

Objectives

The question generally arises, "Why test?" There are reasons for testing arising from both the manufacturers' and the users' points of view. Traditionally, manufacturers have carried out factory tests in order to avoid the costly expense involved with site rectification of deficiencies. Testing is expensive, and manufacturers have no incentive to test low value items except where consequential damage can be caused by the equipment supplied. Figure 10-1 shows a typical centrifugal compressor test stand with several compressors being readied for test,

Many large petrochemical projects involve considerable investment. Plant output value can be measured in staggering amounts of money if value of lost production is calculated. An incorrect pressure switch installed on a compressor may have very little direct financial impact to a compressor manufacturer, but it can cause a loss to the user far in excess of the total value of the compressor package itself. Extra care must therefore be taken in compressor performance tests. In the planning of a project, testing has to be reviewed to:

* Verify design parameters, including performance

* Proof testing of all functions

* Correct faults found

The required lead time for ordering equipment has to take into account all the above factors. Too often the time required for possible design alteration, which may be found necessary, is overlooked. In order to min-

Figure 10-1. Compressors and steam turbines on a large modern test stand (Courtesy of Elliott Company)

imize loss time, each item of equipment can be reviewed for the risk factor involved in its design. The longest time required for modification is in the ordering of raw material. Spare raw material must, therefore, be considered at the time the original order is placed.

The extent of this should be inversely proportional to the manufacturers' experience and directly proportional to the financial consequences of lost production. For example, blank gear sets will allow speed change. Material for guide vanes and impellers will accommodate modifications to aerodynamic performance. Spare material will offset the risk of material defect.

The first test to be considered is not an operational test, but the first major assembly proof test.

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