However, the reasons for failures need to be investigated and the root cause for this failure must be determined to extend the rod life in the future. Fatigue of rods also was considered in To make up a sucker-rod joint using CD, the pin and coupling threads should be cleaned and lubricated with a lubricant that has passed the NACE MR screening test. A continuous strand of composite materials, called "ribbon rods," was developed and field tested.
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Care should be taken when recommending the SM couplings, even though they have longer wear life than T couplings. Carrying out the various procedures described in this section can greatly reduce operating costs and make production more efficient and economical.
Chemical inhibition may not prevent embrittlement. Proper running, handling, and makeup procedures should be followed to speec maximum service from a rod string.
The use of the API taper lengths, of xpec, saves the time of a detailed string design, but the wide availability of personal computers today has eliminated the need to resort to such a shortcut method. The three main grades of steel rods follow:. The downhole production strings may fail for a variety of reasons, some of which have been discussed previously.
Corrosion pits are one type of stress raiser. Further work by Hermanson  using the area relationships and allowable strength of the different grades of steel rods resulted in different derating factors, which are included in API RP 11BR.
The most common rods in use will meet API specifications and will probably be in ft lengths. Friction in the pump holddown plus sediments in the pump-tubing annulus increases the required pump-unseating force. The advent of the personal computer and its continued developments of power and speed allowed more developments of rod-string simulators, 11b Recommendations are presented for derating based on the class wpi the inspected rod, according to the inspection-criteria classes in API RP 11BR.
Sucker-rod strings are lifting a great deal of weight every cycle. The rod string's stretch in Table 4.
Spec 11B Gages | PMC Lonestar
The tensile strength is generally greater thanpsi, while the yield strength is generally greater thanpsi; therefore, these rods could not be classified as API Grade D. Recent discussions have aip a hyperbolic relationship for allowable load using the Gerber parabola, rather than a straightline relationship. However, the ID of the seating nipple determines the fluid load that must be lifted to unseat the pump.
An allowable load or stress curve should be developed to discern during the design of a rod string if it is overloaded, and adjustments should be made to prevent this.
Zaba  detailed the next refinement of sucker-rod loading, which was the organization of the Sucker Rod Pumping Research Inc. Thus, more production may be possible from the well with a tapered string than a straight string using the same-diameter pump.
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This overtravel approximately equals twice the expected value when using steel sucker-rod strings. However, a high tubing-casing-annulus fluid level decreases the load on the rod string when attempting to unseat a pump. Non-API sucker rods generally fall into two groups: Replacing a rod string one rod at a time is not normally a good operating practice; thus, the economic life of a rod string needs to be considered if rods 11 to fail. Well equipment, including sucker rods, must be in good working condition.
The primary factor determining the proportion of each size of rod in the rod string is the size of the pump. The need for carrying out actual rod designs is further augmented by limitations of the published taper percentages; note that taper lengths are the sole function of plunger size which is oversimplification of the design. This is especially problematic if field welds are made and the rods are used in an inadequately protected corrosive environment.
For good operating practices, the minimum yield strength should not be exceeded. They should be selected for wells in which operating stresses do not exceed 50, psi. Combining this with the normally corrosive environmental conditions of water, H 2 S, Sepc 2etc.
It is important to keep the following in mind when screening a well for FRP-rod use:. Old pony rods normally should not be used in the load-carrying part of a new rod strings. Manufacturers of non-API rods should specify the rod's allowable stress.