MP Polymer^TM Technology

Glass Transition Temperature

Glass Transition Temperature, Tg, is a graphical data-set which represents a plastic’s material stability over a series of temperature changes. Most often, the Glass Transition Temperature is found through Dynamic Mechanical Thermal Analysis, ASTM E1640. 3 states in plastics exist.

• The Glassy State (descriptive of plastic being as stiff as it can be – ideal for guides)
• Rubbery State (a plateau between the Tg and Tm, melt temperature)
• Melt State (temperature at which the plastic needs to be to reshape its form) – molding.

A guides best properties against wear and deflection are in the glassy state. The material is the strongest part it can be.

Mechanical Properties

As the modulus of a material lowers in elevated temperature, its mechanical properties do too. The tensile strength, compressive strength, flexural strength, and dimensional stability decrease similar to the transition found from the DMTA analysis. Operating beyond the Tg provides a weaker part which is more susceptible to premature wear, end-of-life, or cracking.

Hygroscopy

PA (Nylon) and PPA (AF or AU) are hygroscopic resins, meaning they absorb and hold moisture. Hygroscopic resins, at 100% Relative Humidity, have weakened molecular bonds within the chemistry of the resin, thus, the mechanical properties of these plastics degrade rapidly. Wells are a wet environment, and in 48 hours @ 200 F, material suppliers state 100% RH is achieved. This lowers the Glass Transition Temperature of PA (Nylon) and PPA (AF or AU) dramatically.

Hygroscopic resins are the worst materials to use for guide materials.

Property Correlation

Why do competitors advertise PPA for 400 F when it loses up to ~80% of its properties at 90 F?

These dated guide materials, PA, PPA, and PPS, all feature Tg temperatures well below well-bore fluids. Therefore, the guides operate in the rubbery state. Operating guides beyond their Tg accelerates the wear of the plastic, which then means guide life is compromised.

In addition to wear properties, the overall mechanical stability of the plastic resin is compromised beyond the Tg. Not only is there an increase in wear, there is also an decrease in chemical resistance and an increase in thermal expansion (a decrease in guide-to-rod bond strength).

MP POLYMER IS CHEMICALLY, THERMALLY, AND DIMENSIONALLY STABLE UP TO 500 F

Wear Study

RFG hired a 3rd party accredited Tribology lab, outside of our industry and outside of material suppliers, to have a non-biased blind study of wear and friction completed.

Wear is directly proportional to friction coefficient, compressive strength, and modulus. Testing was completed with a modified ASTM G133 Standard, Standard Test Method for Linearly Reciprocating Ball-on-Flat Sliding Wear.

However, test is not in full compliance with the standard because:

• The ball radius is 3 mm instead of 4.76 mm
• The normal force is 10 N and 30 N instead of 25 N
• The oscillating frequency is 1.6 Hz and 0.6 Hz instead of 5 Hz
• The test duration is longer than 16 minutes and 40 seconds, however, the sliding distance is 100 meters
• Lubrication was applied
• Heat was applied

As expected, the high glass PAEK material did not show measurable wear, but wear was observed. In oilfield applications, this transfers the wear into the tubing, which is why the market shies away from 40% glass filled materials. In fact, the market typically accepts 33% glass as the most allowable before tubing wear occurs. The less glass the better.

RFG MP Polymer Technology allows the resin system to be the wear surface, not the glass. We utilize glass filler as a strength-adder to the resin system, rather than relying on glass for a wear surface, since glass in excess can be abrasive to tubing. MP Polymer Products feature 20% Glass, we believe the lowest glass filled guiding material in the market.

Lower is better.

Friction

Friction has long been a concern for rod pumped wells, especially as the limits are constantly pushed in deep deviated and horizontal applications. Rod string design programs cite that friction coefficients INCREASE with sucker rod guides, by a factor of 1.5x. Respected beam lift handbooks in the industry also cite guides having a higher friction coefficient than steel-rod-on-steel-tubing, but there is no source for the data. RFG reached out to the authors of these handbooks, they cited referencing public domain statements, with no specific references to back up the claims from the text.

Friction data was computed from the G133 Wear Study above.

The results are intriguing. Materials with higher glass content have a lower coefficient of friction. We equate this to glass being a slick, non-porous and hard surface. As you add more glass, your coefficient of friction goes down. However, added glass content does affect the wear on the tubing. 33% glass has long been the industry respected threshold of glass content and sucker rod guide materials prior to guide materials being significantly abrasive to tubing.

Furthermore, all sucker rod guide materials, filled or unfilled, are proving to have a lower coefficient of friction against steel than the rod. Any person can run their hand or finger along ANY manufacturer’s rod guide material surface, rub it along a rod section, and the rod section clearly creates more frictional resistance.

Rod String Design programs cite steel rods on steel tubing as 0.2. RFG MP Polymer products have a COF of 0.1. All Guided rods produce less friction and drag load than slick sucker rods.