skoczylas-pliska rod testing undertorsiontension bending
TRANSCRIPT
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Rod Testing Under Torsion, Tension &
Bending
Paul Skoczylas, C-FER
Ross Pliska, Alberta Oil Tool
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Objective
Why are failures in the field different from
lab test results? In the coupling (lab tests fail in the rod body)
At lower torque
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Outline
Strength of rod body vs. connection in
torsion/tension testing Field conditions vs. laboratory conditions
Effect of make-up procedures
Effect of bending
Conclusions
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Rod Test Procedure (Tension/Torsion)
1. Thoroughly clean pin and coupling
2. Apply lubricant as per manufacturers
recommendation 3. Make-up connection hand-tight
4. Increase torque until make-up is reached (either
torque or circumferential displacement criterion) 5. Drop to zero torque
6. Apply axial load (and keep constant for durationof test)
7. Increase torque at constant rate until failure For rod body test with no connection, start at
step 6.
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1 Rod Body, No Connection
0
1000
2000
3000
4000
5000
6000
7000
0 0.2 0.4 0.6 0.8 1
Turns
Torqu
e(ftlb)
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1 Modified Pins on 2 Rod
0
1000
2000
3000
4000
5000
6000
7000
0 0.2 0.4 0.6 0.8 1
Turns
Torque
(ftlb)
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Connection vs. Body
1 Rod body fails at ~2000 ftlb, yields at
~1000 ftlb 1 Modified pin with 1 slimhole coupling
fails at 5500-7000 ftlb, yields at 2000-5000
ftlb
Rod body should always fail first
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Field vs. Laboratory Conditions
Lab:
Connections cleaned thoroughly prior to make-up
Precisely-controlled make-up (either torque or
circumferential displacement) Failures in rod body
Field:
Connections may not be thoroughly cleaned
Make-up is not usually precise
Failures occur in connections and body
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Why the Difference?
An investigation is ongoing
Two factors considered so far: Make-up procedures!
Rods are often run in deviated wellsdoes this
affect loading on couplings?
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Make-Up Tests
Performed with 1.5 Grade 97 rods with
1.125 pins, and regular High Strength (HS)couplings
Published torque rating is 3750 ftlb at
90,000 lb axial load All tests had 90,000 lb axial load applied
after make-up
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Test #1, 2
Thread lubricant applied to threads and torque
shoulder (over-lubrication)
Made-up by vendor using field practices
Connection failures at 2910, 3108 ftlb (below
torque rating)
0
500
1000
1500
2000
2500
3000
3500
0 0.5 1 1.5 2 2.5 3 3.5
Turns
Torque(N
m)
Test #1
Test #2
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Tests #3, 7, 8
Connections made-up by vendor, with proper
lubrication, using field practices
Connection failure at 4830, 5496, 5296 ftlb(above torque rating)
0
1000
2000
3000
4000
5000
6000
0 1 2 3 4 5
Turns
Torque(Nm)
Test #3
Test #7Test #8
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Tests #4, 6
Test #4
Made up and broken out by vendor Cleaned and properly lubricated by test lab
Rod failure at 5899 ftlb
Test #6 Cleaned and properly lubricated by test lab
Two make-breaks before test to failure
Slight galling noticed on make-breaks
Rod failure at 6178 ftlb
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Tests #4, 6
0
1000
2000
3000
4000
5000
6000
7000
0 0.5 1 1.5 2 2.5 3
Turns
Torque(Nm)
Test #4Test #6
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Tests #5, 11
Pins cleaned at test lab
Coupling containing anti-corrosion lubricant(off the shelf) used without cleaning
Connection failures at 2850 & 3000 ftlb
0
500
1000
1500
2000
2500
3000
3500
0 0.5 1 1.5 2 2.5 3 3.5
Turns
Torque(
Nm)
Test #5Test #11
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Test #9, 10
Cleaned and properly lubricated by test lab
In test #10, Moly-based lube was used Failure in rod at 5848 & 5901 ftlb
0
1000
2000
3000
4000
5000
6000
7000
0 1 2 3 4 5
Turns
Torq
ue(Nm)
Test #9
Test #10
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Summary of Make-up Tests
Cleaned by test lab:
5848, 5899 (M-B), 5901, 6178 (M-B) ftlb Rod body failures
Cleaned by vendor and made up with field
practices: 4830, 5296, 5496 ftlb
Connection failures
Not cleaned and/or over-lubed: 2910, 2850, 3000, 3108 ftlb
Connection failures
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Make-up
Properly clean BOTH pins AND coupling
Minimumwipe all faces and threads
Best practiceuse degreaser
Apply only recommended amount of lubricant
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Effect of Bending
A large portion of torque resistance is fromfriction on the torque shoulder
In bending, contact force is increased onone side and decreased on other sidewill
this affect the torque resistance? Tests were conducted with 1.25 Grade 75
Rods (torque rating 2100 ftlb at 50,000 lbs
axial load) Test procedure was similarbending is
applied after make-up, before axial load
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Test Apparatus Capacity
2x10 rods (Std.
tests are 2x2) 12,000 ftlb
300,000 lb axial
>200/100ft bending
in connection
region, via speciallydesigned bearings
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Results
Maximum Torque
Straight: 3163, 3476, 3137 ftlb
10/100ft:
3113, 3155, 3105 ftlb All failures in rod body
No significant difference in maximum torque
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Results
0
500
1000
1500
2000
2500
3000
3500
4000
0 2 4 6 8 10
Turns
Torque(ftlb)
Straight 1
Straight 2
Straight 3
Bent 10/100ft 1
Bent 10/100ft 2
Bent 10/100ft 3
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What Happens During/After Make-up?
0
500
1000
1500
2000
2500
0 0.1 0.2 0.3 0.4 0.5
Turns
Torque(
ftlb)
Straight 1
Straight 2
Straight 3
Bent 10/100ft 1
Bent 10/100ft 2
Bent 10/100ft 3
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What Happens During/After Make-up?
Incremental make-up occurs at a torque that
is less than the make-up torque Cause axial load unloads shoulder
This occurs at:
Straight: 1480, 1530, 1600 ftlb
10/100ft: 1285, 1350, 1480 ftlb
There may be a small effect of bending from
0-10/100ft, but it is not statistically
significant
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Conclusions
Properly cleaned, lubricated, and installed,
connections are stronger than the rod body! If connectionsboth pin and couplingare
not properly cleaned and lubricated, low
torque capacity results Bending does not reduce torque capacity