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MATERIALS SELECTION & DESIGN FIGURE 1
Analysis Result of Oil and Gas The salt contained in the oil was
34.77 mg/L on May 3, and 39,039.23 mg/L on June 17. There was big differ- ence between them.
Samples for Failure Analysis The cracked coupling with a pin made ]X I\ \PM ÅMTL MVL 6W
IVL IV ]V][ML
coupling with a pin made up at the mill MVL 6W _MZM [IUXTML NWZ NIQT]ZM analysis.
Macro-Fractography The wider part of the crack was basi-
cally along the longitudinal direction, and a thin crack extended in the direction of 75 degrees with a coupling generatrix at \PM UQLLTM WN \PM KW]XTQVO .QO]ZM The fracture was covered with corro-
sion deposits. There were constringent radial lines from the crack origin on the \PZMIL []ZNIKM IN\MZ KTMIVQVO .QO]ZM The crack origination area was compara- \Q^MTa ÆI\
FIGURE 2
Macro fractography showed that the coupling fracture was brittle.
Thread and Dimension Inspection Inspection showed that the coupling connection met API SPEC 5B1 SPEC 5CT.2
and API There was no obvious pitch
KPIVOM NWZ \PM 6W KZIKSML KW]XTQVO
\PIV I\ Q\[ ÅMTL MVL VW\ UILM ]X IVL UU JQOOMZ \PIV \PI\ WN \PM 6W
KW]XTQVO I\ \PM ÅMTL MVL ! ! UU
made up with the pin. The J dimension _I[
UU I\ \PM ÅMTL MVL WN \PM 6W
1 connection and 7.49 mm at the mill MVL WN \PM 6W
KWVVMK\QWV
1\ _I[ M[\QUI\ML \PI\ \PM KWVVMK-
tion was not over-tensioned during use and the make-up torque was higher at the mill end of the connection than that I\ \PM ÅMTL MVL Q M MVOIOML \PZMIL[ I\ the mill end of the connection were ap- proximately two threads more than that I\ \PM ÅMTL MVL
Internal pressure change along with date in tubing and casing.
Crack origination morphology.
The coupling crack morphology. NACE International, Vol. 51, No. 4
April 2012 MATERIALS PERFORMANCE 59