|
Defective Oilfield Casing Coupling
An oil well casing with an ultra flush coupling was
being set. The lift plug was set, the casing joint
was lifted, the lift plug dislodged, and the casing
fell to the rig floor, injuring a rig hand. The
casing coupling is shown in Photograph A.
Photograph A: Subject casing coupling
mouth.
The measurement of the coupling mouth, as shown in
Photograph B indicated that the casing outside
diameter was 8 13/16". Thus, the coupling mouth was
flared by approximately 9/64" or 0.140 inches.
Photograph B: Close-up view of
measurement of coupling mouth and surface
deformation.
The magnitude of the casing mouth is further
illustrated in Photograph C
Photograph C: Overall view of casing
coupling mouth.
Visual examination revealed that the subject casing
was flared as a result of improper machining when
the subject 8 5/8" casing coupling was manufactured.
The flare (increase in casing outside diameter) at
the threaded end of the subject casing is indicative
of radial force being exerted from the interior of
the casing. This inside force is most probably the
result of radial pressure from the tooling used to
cut the casing internal threads. If excessive
tooling pressure is applied and/or if insufficient
support is not given to the casing outside surface
during machining, the result is permanent, plastic
deformation of the mouth of the casing. This
permanent plastic deformation will result in flaring
or lipping of the end of the casing.
Back to top
|
Dr.
R. Craig Jerner, Ph.D., PE specializes in accident
investigation and metallurgical failure analysis,
with over 30 years experience as a metallurgical
consultant and accident investigator. He has
testified as a metallurgical expert in over 250
depositions and more than 70 court appearances. If you or someone you know should need the services of Dr. Jerner and J.E.I. Metallurgical, please visit our web site at the buttons below, or e-mail Dr. Jerner --- 