skoczylas-pliska rod testing undertorsiontension bending

8/12/2019 Skoczylas-Pliska Rod Testing UnderTorsionTension Bending

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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

skoczylas-pliska rod testing undertorsiontension bending

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