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- and we emphasize that there are no substitutes for such
“real world” testing
- it is possible, however, to develop test methods that offer
considerably greater insight than wind tunnel analysis. A conceptual “erosion
flow loop” is shown in Figure 9.24. Here, a lightweight mud (or water flow
with 1-3% sand) recirculates in a system requiring minimal space or pump
power. Test models, cleaned and coated with epoxy paint, are run for several
minutes, before they are removed for visual examination. Results are almost
always identical to those obtained from damaged field parts.
Erosion test section
Rotating
siren, turbine,
or stationary
strainer,
coated with
epoxy paint
Flow
straighteners
1-3% sand in
water
mixture
Pump
Figure 9.24.
Erosion flow loop.
If the above erosion flow loop is operated in the horizontal position, it is
possible for sand to accumulate at the bottom due to gravity segregation. This
can be avoided by running the system vertically, so that sand is uniformly
dispersed throughout the cross-section of flow. We emphasize that wear
patterns obtained from wind tunnel visualization apply only if the metal never
erodes. In practice, it is the interaction between fluid erosion and actual metal
removal that results in observed erosion. Wind tunnel testing will help in
understanding erosion, but will never completely solve the problem.
9.5.5 Attenuation testing.
Elsewhere in this topic, we have pointed out the dangers inherent in
drilling mud signal attenuation evaluation using finite-length flow loops excited
by periodic mudpump pistons. Essentially, the effects of amplitude variations
due to standing wave node patterns must be removed in order to provide true
estimates for thermodynamic loss. This process is difficult computationally.
Even when it can be accurately performed, there is always lingering doubt that
the buried flowloop used may contain undocumented area discontinuities which
may render the acoustic data useless.
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