Black Mamba - For Compression

Legacy rod guides are out, Black Mamba is in.

Having the potential to cause more harm than good when compression is present, legacy rod guides have pushed failure modes from hole-in-tubing to accelerated rod parts. Compressive instances along the rod string are inevitable. Between inertia, slug flow, tagging, seating the pump - sucker rods see compression.

Compression causes rod buckling.

Rod buckling creates bending moments.

Bending moments set the location of rod failure.

Flexibility

With a single fin design, The Black Mamba is the only molded sucker rod product in existence that truly does not inhibit sucker rod flexbility. The reduced cross-sectional area combined with our engineered material options allows for unprecedented component flex and a complete elimination of bending moments along the sucker rod when used properly.

 

Relative Area Moment of Inertia
Lower value = greater geometric flexbility.
Monster Legacy Thermoplastic (I = ~0.775)
Legacy Phenolic (I = ~0.696)
Black Mamba (I = ~.294 max)

Not even the softest thermoplastic material combined with legacy guide designs has the flexibility that we offer. 

AMOI of Sucker Rod Guides and The Black Mamba

Critical Buckling Load

The critical buckling load is the maximum load a member can take that will not lead to lateral deflection (instability; buckling). As loads are applied to a sucker rod greater than this calculated value, the column (rod) will move laterally (rod-into-tubing), creating unstable equilibrium.

Compressive loads applied to sucker rods are not as detrimental as one would think. Instead, the buckling behavior creates bending moments, causing far greater stresses on the sucker rod at the bending moment origin, in comparison to normal operating tensile loads and stresses. Bending moment stresses are what sets the eventual failure location of sucker rod parts.

S-N Curves

As repetitive stress magnitude increases, the number of expected cycles to failure decreases, resulting in a shorter life for the product. Although a rod string design may be engineered correctly for standard tensile loads on the up-stroke, during compressive moments, the rod string design rendered is no longer accurate.

The bending moments created during compression occur at the upset-forging to rod-body transition or at the edges of rod guides, and is THE reason for common rod parts and sucker rod failure. Of course, for all failures at these locations, corrosion will be a contributor, leading to the common definition of Corrosion Fatigue. High tensile stresses are present at the moment of deflection, and those stresses far exceed the long-time respected Modified Goodman Diagram which drives rod string design best-practices.

In sucker rod dynamics, one of the greatest improvements to the system is ELIMINATING BENDING MOMENTS and reduction of chaotic behavior. With The Black Mamba, compression, which cannot entirely be eliminated, must be dealt with. Compression can be present and the sucker rod not buckle due to the constant reinforcement to the central axis of tubing through The Black Mamba's extended length design. This eliminates the astronomical acceleration in time to fatigue failure caused by high tensile stresses related to buckling.

Rod Fatigue

Strange to think about - compression causes drastic tension stresses along the rod, increasing stress cycles and stress magnitude. Part failure for any component never fails in pure compression. Instead, the failure mode is actually shear, which is a combination of compressive and tensile stresses which in rod lift's case, are a result of instability.

Keeping compression normal to the sucker rod's cross-section is critical. On a long slender column, small compressive loads lead to buckling near instantaneously.

e.g.: A compressive load of 6,000 lbs on a legacy guided 3/4" rod, 4 per, buckles and leads to tensile stresses eclipsing T/2.8. Although this seems like an excessive compressive load, it is only 25% of buoyant string weight in a deep modern well, and less than a 10,000 ft. 1.5" pump fluid load released during the up-to-down stroke transition.

Axial compliance between the tubing and rod, thanks to The Black Mamba's constant reinforcement, eliminates these bending moments, in-turn eliminating excessive tensile stresses applied to the sucker rod far greater than their design intended use (T/~2.8).