Aegis Tech Line · Sucker Rod Joint Makeup give the proper procedure to ensure adequate joint...
Transcript of 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.
Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 10, March 2019
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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.
Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 10, March 2019
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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
Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 10, March 2019
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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
Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 10, March 2019
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Mill Defect
Notch Fatigue Failure
Under‐Torquing Damage to the first full thread root
Under‐Torquing Damage to the coupling
Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 10, March 2019
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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
Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 10, March 2019
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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
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