STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

534 Drilling and Well Completions
Parts Testing. Individual parts of a unit may be tested separately if the holding
fxtures simulate the load conditions applicable to. the part in the assembled unit.
Test Fixtures. Test fixtures shall support the unit (or part) in essentially the
same manner as in actual service, and with essentially the same areas of contact
on the load-bearing surfaces.
Test Procedure.
1. The test unit shall be loaded to the maximum rated load. After this load
has been released, the unit shall be checked for useful functions. The useful
function of all equipment parts shall not be impaired by this loading.
2. Strain gages may be applied to the test unit at all points where high stresses
are anticipated, provided that the configuration of the units permits such
techniques. The use of finite element analysis, models, brittle lacquer, etc.,
is recommended to confirm the proper location of strain gages. Threeelement
strain gages are recommended in critical areas to permit determination
of the shear stresses and to eliminate the need for exact orientation
of the gages.
3. The maximum test load to be applied to the test unit shall be 0.80 x R x
SF,, but not less than 2R. Where R equals the calculated load rating in
tons, SF, is design safety factor.
4. The unit shall be loaded to the maximum test load carefully, reading strain
gage values and observing for yielding. The test unit may be loaded as
many times as necessary to obtain adequate test data.
5. Upon completion of the load test, the unit shall be disassembled and the
dimensions of each part shall be checked carefully for evidence of yielding.
Determination of Load Rating. The maximum load rating may be determined
from design and stress distribution calculations or from data acquired during a
load test. Stress distribution calculations may be used to load rate the equipment
only if the analysis has been shown to be within acceptable engineering
allowances as verified by a load test on one member of the family of units of
the same design. The stresses at that rating shall not exceed the allowed values.
Localized yielding shall be permitted at areas of contact. In a unit that has been
load tested, the critical permanent deformation determined by strain gages or
other suitable means shall not exceed 0.002 in./in. If the stresses exceed the
allowed values, the affected part or parts must be revised to obtain the desired
rating. Stress distribution calculations may be used to load rate the equipment
only if the analysis has been shown to be within acceptable engineering
allowances as verified by a load test of one member of the family of units of
the same design.
Alternate Test Procedure and Rating. Destructive testing may be used provided
an accurate yield and tensile strength for the material used in the equipment
has been determined. This may be accomplished by using tensile test specimens
of the actual material and determining the yield strength to ultimate strength
ratio. This ratio is then used to obtain the rating R (ton) of the equipment by
the following equation:
(4-19)