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Atlas Bradford is proud to announce an improved
version of our proven NJO integral joint connection, ADVANCED NJO.
ADVANCED NJO will offer performance improvements in compression
strength, bending, torsion capability, and external pressure sealing
while maintaining interchangeability with the current NJO design.
ADVANCED NJO will be available in September 1999.
ADVANCED NJO Design Process
The ADVANCED NJO design process began with a complete
finite element analysis (FEA) of the current NJO design utilizing
ANSYS and ABACUS codes. Assuring that the connection mechanics were
completely understood and that stress levels were maintained within
the elastic limit of the material, each torque shoulder and thread
form modification were evaluated for a variety of load conditions.
Seal surface bearing pressures were analyzed to assure that the
proven NJO seal mechanics were maintained. Before release, the performance
several popular sizes of the ADVANCED NJO will be verified by physical
testing at Grant Prideco’s Tubular Test Facility.
Improvements in Compression and Bending Strength
ADVANCED NJO compression and bending efficiency
will be a minimum of two times that of our current design.
Maintaining our steadfast dedication to rate our products within
their elastic capability, these improvements were accomplished by
utilizing an increased torque shoulder area and an improved thread
Compared to the current design, the ADVANCED NJO torque shoulder
contact area is significantly increased. In addition, the torque
shoulder configuration was modified to provide additional radial
support from adjacent pin and box surfaces.
Contrasting with the current NJO design which relies
entirely on the torque shoulder contact area for its compression
strength, ADVANCED NJO gains a significant increase in compression
strength gain by incorporating an improved premium thread form that
supports the majority of the compression load. The thread from incorporates
a negative (hooked) tension flank and minimizes axial clearances.
Addition of the External Metal-to-Metal Pressure
Seal
External pressure sealing of the ADVANCED NJO is
enhanced with the addition of a metal-to-metal external pressure
seal. Seal bearing pressure results from radial stress that is generated
by the interference fit of the seal surfaces that is further enhanced
from the energization of the applied external differential pressure.
The design provides external seal capability that acts independently
of applied axial loads, torsion load, and field make-up conditions.
Interchangeable with the Current NJO Design
Complete interchangeability of ADVANCED NJO with
the current NJO design was maintained. When ADVANCED NJO is released
for production, the current NJO design will no longer be manufactured.
The New ADVANCED NJO will be completely compatible with existing
casing inventories. No crossovers will be required. Disposal of
out-of-date remnants will not be necessary.
Current NJO
The finite element plot for the current design of NJO for 5 in. 23.20
ppf P-110 is shown for a compression load equal to the connection’s
rating of 29.9% of the pipe body. The open gaps on the thread compression
(stab) flank indicate that the compression load is supported entirely
by the torque shoulder contact area. It should be noted that the stress
levels are below the elastic limit of the P-110 material, no elastic
strain is present.
Current NJO
The finite element plot for the current design of NJO for 5 in. 23.20
ppf P-110 is shown for a compression load equal to the connection’s
rating of 59.8% of the pipe body. At the torque shoulder contact area,
the plot indicates the occurrence of significant plastic strain indicating
that the elastic limit of the P-110 material has been exceeded.
ADVANCED NJO
The finite element plot for the ADVANCED NJO design for 5 in. 23.20
ppf P-110 is shown for a compression load equal to the connection’s
rating of 59.8% of the pipe body. In addition to the increased torque
shoulder contact area, a significant portion of the compression load
is supported by the ADVANCED NJO’s improved thread form as indicated
by contact of the thread compression (stab) flanks. The plot indicates
that the stress levels are below the elastic limit of the P-110 material,
no elastic strain is present.
Normalized Seal Pressure
The above graph displays a comparison of the normalized contact pressure
(seal bearing pressure divided by internal pressure) for 5 in. 23.20
ppf current and ADVANCED NJO designs with compression with internal
pressure to produce a VME pipe body stress equal to 90% of the P-110
yield strength. Note that the seal bearing pressure for the Advance
NJO exceeds that of the current design at their respective compression
ratings of 29.9 and 59.8%. At a 59.9% compression load, the standard
design displays degradation and shifting of the seal contact pressure.
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