Peh: Drilling Problems and Solutions Publication Information Petroleum Engineering Handbook

Drillpipe Failures
Twistoff
Parting

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Pipe failure as a result of collapse or burst is rare; however, under extreme conditions of high
mud weight and complete loss of circulation, pipe burst may occur.
Fatigue is a dynamic phenomenon that may be defined as the initiation of microcracks and their
propagation into macrocracks as a result of repeated applications of stresses. It is a process of
localized progressive structural fractures in material under the action of dynamic stresses. It is
well established that a structural member that may not fail under a single application of static
load may very easily fail under the same load if it is applied repeatedly. Failure under cyclic
(repeated) loads is called fatigue failure. 
Drillstring fatigue failure is the most common and costly type of failure in oil/gas and geothermal
drilling operations. The combined action of cyclic stresses and corrosion can shorten the life
expectancy of a drillpipe by thousand folds. Cyclic stresses are induced by dynamic loads caused
by drillstring vibrations and bending-load reversals in curved sections of hole and doglegs
caused by rotation. Pipe corrosion occurs during the presence of O
2
, CO
2
, chlorides, and/or H
2
S.
H
2
S is the most severely corrosive element to steel pipe, and it is deadly to humans. Regardless of
what may have caused pipe failure, the cost of fishing operations and the sometimes
unsuccessful attempts to retrieve the fish out of the hole can lead to the loss of millions of dollars
in rig downtime, loss of expensive tools downhole, or abandonment of the already-drilled
section below the fish. 
In spite of the vast amount of work that has been dedicated to pipe fatigue failure, it is still the
least understood. This lack of understanding is attributed to the wide variations of statistical
data in determining type of service and environment of the drillstring, magnitude of operating
loads and frequency of occurrence (load history), accuracy of methods in determining the
stresses, quality control during manufacturing, and the applicability of material fatigue data.
Although pipe failure cannot be eliminated totally, there are certain measures that can be taken
to minimize it. Fatigue failures can be mitigated by minimizing induced cyclic stresses and
insuring a noncorrosive environment during the drilling operations. Cyclic stresses can be
minimized by controlling dogleg severity and drillstring vibrations. Corrosion can be mitigated
by corrosive scavengers and controlling the mud pH in the presence of H
2
S. The proper handling
and inspection of the drillstring on a routine basis are the best measures to prevent failures.
Borehole instability is the undesirable condition of an openhole interval that does not maintain
its gauge size and shape and/or its structural integrity. The causes can be grouped into the
following categories: mechanical failure caused by in-situ stresses, erosion caused by fluid