Page 251 - Shale Shakers Drilling Fluid Systems

EQUIPMENT GUIDELINES 233
have a total screen area at least five times the
cross-sectional area of the suction line so it will
not restrict flow. An extended handle arrange-
ment reaching to the tank surface is desirable
to allow the screen to be pulled during service
and cleaned.
An expanded metal screen prevents objects
(such as gloves, buckets, pieces of clothing,
chunks of rubber, etc.) from plugging the suc-
tion line or fouling the impeller. A bucket,
turned so that the bottom fits into the suction
line, can be difficult to diagnose and locate.
A box made from expanded metal that cov-
ers the suction can prevent these disasters.
If two alignment yokes are welded to the
tank walls to hold a one-inch pipe handle, the
screen can be removed, cleaned, and easily
returned to the suction opening. Without these
alignment yokes, reseating the expanded metal
box is difficult.
4. Suction and discharge lines should be properly
sized and as short as practical. Flow velocities
should be in the range of 5 to 10 ft/sec. Less
than 5 ft/sec causes solids to form a tight layer
obstructing the bottom of horizontal lines. At ve-
locities at or exceeding 10 ft/sec, pipe-turns tend
to erode, headers do not distribute properly, and
usually there will be cavitation in the suction
lines. To calculate the velocity inside the pipe, 6. Install a pressure gauge between the pump
use the following equation:
Suction lines should contain no elbows, swages,
or reducers closer than three (3) pipe diameters
to the pump suction flange.
Horizontal pipes will fill with solids until the
flowrate reaches 5 ft/sec. Barite in equalizing
lines between mud tanks is normally settled
until the velocity between the tanks reaches
5 ft/sec. Increasing the diameter of connec-
tion lines only causes more barite to settle.
Above 10 ft/sec, pressure losses in the pipe
become too great. Elbows and swages tend to
cause turbulence in the flow stream, which
can lead to cavitation.
5. Eliminate manifolding. One suction and one
discharge per pump is most cost effective over
time. Do not manifold two pumps on the same
suction line. Do not pump into the same dis-
charge line with two or more pumps.
"Flexibility" of piping so fluid can be pumped 7. Keep air out of the pump by degassing the mud,
from any tank through any equipment to any
other tank has created more problems over
the years than just about any other concept.
A properly plumbed system should only require
one suction and one discharge for each piece
of solids removal equipment. Ignoring this
rule allows rig hands the opportunity to open
or close the wrong valves. A leaky or incor-
rectly opened valve can reduce drilled-solids
removal efficiency by up to 50%. This trans-
lates to an expensive drilling fluid system.
This problem can be eliminated by storing an
extra pump and motor. Arrange the centrifu-
gal pumps and motors so that they may be
easily replaced. If a pump or motor fails, sim-
ply replace the unit. The damaged unit can be
replaced during routine maintainence.
Two centrifugal pumps in parallel will not
double the head available to equipment be-
cause a centrifugal pump is a constant head
device. For example, visualize a standpipe that
is constantly filled with fluid. If two standpipes
of approximately the same height are con-
nected, the flow from both pipes will almost
equal the flow from one standpipe. If fluid
stands lower in one standpipe than the other,
fluid will flow from the highest standpipe to the
lowest standpipe. This same flow occurs when
two pumps are connected in parallel—fluid will
flow backwards through one of the pumps.
discharge and the first valve. When the valve
is closed briefly, the pressure reading may
be used for diagnostic evaluation of the pump
performance.
A centrifugal pump uses the smallest amount
of power when no fluid is moving through the
pump (that is, when the discharge valve is
completely closed). If the valve remains closed
for longer than five minutes, the fluid within
the pump will become hot from the impeller
agitation. This hot fluid may damage the seals.
Closing the valve for a short time allows a
good reading of the no-flow head produced by
the pump. This reading should be compared
with the pump manufacturer's charts. The
diameter of the impeller can then be deter-
mined. After the pump has been in service
for a period of time, the reading will assess
the condition of the impeller. This eliminates
the need to dismantle the pump for inspec-
tion. If the manifold pressure is incorrect,
reading the pump no-flow discharge head will
assist in troubleshooting.
having adequate suction line submergence, and