aegis tech line · sucker rod joint makeup give the proper procedure to ensure adequate joint...

Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 10, March 2019

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SUCKER ROD FAILURE ANALYSIS This volume deals with sucker rod failures and analysis of those failures. This is a problem in the oilfield particularly in mature fields where this type of oil production is very common.

Sucker Rod Body Breaks Sucker rod body failures (breaks) are shown in the drawing below:

Except for case hardened rods, body breaks (including those at the beginning of the rod to pin taper) will invariably have the appearance shown in the drawing below. The size of the smooth surface area reflects that the until the area is reduced to where the yield strength of the rod is reached, the crack continually opens and closes peening the surface. Once the yield strength of the steel is exceeded, only a few pump strokes are required for the complete failure of the rod body and generation of the modified typical tensile cup/cone failure appearance.

Sucker Rod Coupling Breaks With standard couplings, the metal cross‐sectional area is large compared to other cross‐sections of the rod string components. This results in corrosion failures being infrequent.


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Sucker Rod Pin Breaks While corrosion as a cause of failure in sucker rod pin breaks is extremely rare, failures when the pin and coupling are not properly mated are frequent. The principle cause of this is inadequate torque. Inadequate torque causes slight separation at the coupling and bin bearing surfaces with a slight bending at this interface. Under these conditions, the threads act as stress raisers with failure occurring within the threaded section of the pin. The drawing below lists the various conditions for pin failures. Failures in the undercut area are unusual except in thin wall couplings. When failures occur frequently in the pin threads, API RP 11BR, Section 4 on Sucker Rod Joint Makeup give the proper procedure to ensure adequate joint torqueing.

Endurance Limit Failure A factor frequently overlooked in sucker rod failure analysis is the possibility of the Endurance Limit having been exceeded. When a rod has a multiple crack appearance as in the image below, an Endurance Limit failure has occurred. All steel items that undergo repeated stress reversals will eventually fail by exceeding the Endurance Limit.

The curves below illustrate the Endurance Limit for a steel immersed in air and in water. Steel specimens for these tests have a smooth surface without any apparent stress raisers. When immersed in water, the electrochemical reaction will develop minute pits that serve as stress raisers to reduce the Endurance Limit.

Sucker rod design is based on the water conditions with a stress reversal range beyond the knee of the curve. With this stress range and a good corrosion control program, at lease 108 cycles should be possible before the Endurance Limit is reached. When wells are pumping from gas drive reservoirs with less than 25% water, the rods will be oil wet and the curve for air will control the Endurance Limit. With this condition, sucker rods will last for many years.


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Propagation of Fatigue Failure The drawing and photograph below illustrate the propagation of fatigue failure in a rod:

Photographic Evidence of Sucker Rod Failures Provided below are photographs of different types of sucker rod failures.

H2S Corrosion

CO2 Corrosion Pit


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Abrasion on Coupling

Wear on Coupling

Erosion‐Corrosion in Rod Guide

Overtightening Sucker rod pin overtightened using power tongs. Note the

necking down of the pin undercut

Stuck Sucker Rod Pulled In‐Two Sucker rod pulled in two when a stuck sucker rod string was

overpulled


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Mill Defect

Notch Fatigue Failure

Under‐Torquing Damage to the first full thread root

Under‐Torquing Damage to the coupling


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Mishandling During Transportation

REFERENCES

Downhole Diagnostics

Weatherford Manual – Sucker Rods

Dover – Sucker Rods

Corrosion Detection and Control Handbook – Champion Chemicals

API Recommended Practice 11BR, Ninth Edition, August 2008 – Sucker Rods Order copy through API


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Aegis Facilities / Locations

CONTACT NUMBER: For all Aegis locations, call the toll‐free number and select the from the options presented.

Toll‐free number ‐ (855) 532‐2033

Corporate Headquarters Houston

4560 Kendrick Plaza Dr., #190 Houston, TX 77032

Permian BasinMidland

2200 Market St. Midland, TX 79703

Permian BasinAbilene

4410 Vista Grande Abilene, TX 79606

Permian Basin Breckenridge 566 FM 2231 E

Breckenridge, TX 76424

Permian BasinCarlsbad

2411A East Greene Street Carlsbad, NM 88220

Permian BasinForsan

300 West 1st St. Forsan, TX 79720

Permian Basin Lubbock

13622 Hwy 87 S. Slaton, TX 79423

Permian BasinMonahans

1332 PR Thrasher Ln. Monahans, TX 79756

East TexasKilgore

4524 State Hwy 42 N. Kilgore, TX 75662

East Texas Teague

931 W. Hwy 84 Teague, TX 75860

East Texas (North Louisiana)Haughton

140 Sligo Industrial Dr. Haughton, LA 71037

South TexasFreer

5743 Hwy 44 Freer, TX 78357

South Texas Asherton

664 Hwy 190 Asherton, TX 78827

South TexasCuero

424 U.S. Hwy 87 S. Cuero, TX 77954

South TexasJourdanton

8229 S. State Hwy 16 Jourdanton, TX 78026

South Texas San Antonio

311 N. Frank Luke Dr. Building 1440, Suite #103 San Antonio, TX 78226

South LouisianaElizabeth

3552 Highway 10 Elizabeth, LA 70638

South Louisiana (E. TX)Raywood

203904 Hwy 90 East Raywood, TX 77582

Mid‐Con Ratliff City

P.O. Box 98, 1500 Old Hwy 7 Ratliff City, OK 73481

Mid‐ConEl Reno

801 N. Willie L. Minor, #B‐1 El Reno, OK 73036

Mid‐ConHennessey

1117 S. Main Street Hennessey, OK 73742


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