CA1249654A - Quality control for sucker rods - Google Patents
Quality control for sucker rodsInfo
- Publication number
- CA1249654A CA1249654A CA000483527A CA483527A CA1249654A CA 1249654 A CA1249654 A CA 1249654A CA 000483527 A CA000483527 A CA 000483527A CA 483527 A CA483527 A CA 483527A CA 1249654 A CA1249654 A CA 1249654A
- Authority
- CA
- Canada
- Prior art keywords
- rod
- load
- elasticity
- modulus
- elongation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
QUALITY CONTROL FOR SUCKER RODS
Abstract of the Disclosure A method for testing fiberglass sucker rods wherein the rod is pulled to a predetermined stress level while measuring the load, elongation and acoustic emissions. The load versus displacement is plotted in real time while the measured values are used to calculate the modulus of elasticity for various load ranges. From the measure-ments and calculated modulus of elasticity the quality of the rod can be determined.
Abstract of the Disclosure A method for testing fiberglass sucker rods wherein the rod is pulled to a predetermined stress level while measuring the load, elongation and acoustic emissions. The load versus displacement is plotted in real time while the measured values are used to calculate the modulus of elasticity for various load ranges. From the measure-ments and calculated modulus of elasticity the quality of the rod can be determined.
Description
~24~654 ~-8939 QUALITY CONTROL FOR SUCKER RODS
.
Background of the Invention m e present invention relates to the production of crude oil wherein beam pumping units are used to actuate downhole pumps to lift the crude to the surface. Sucker rods are used to couple the beam pump-ing unit at the surface to the reciprocating pump located at the bottomof the well. Sucker rods are conventionally provided with male threads at each end and are coupled together by coupling units to form a con-tinuous rod from the surface to the bottom of the well. Normally, the sucker rods are made of steel and provided with suitable threaded ends and flat sections to permit the use of wrenches in coupling the rods together. While steel rods are satisfactory, in some installations it would be desirable to use rods formed from non-corroding materials. This is especially the case when producing wells that contain sour crude, that is, crude having a high sulfur content that corrodes the rods and increases the maintenance required for the pumping unit.
In order to overcome the problem of corrosion in sour wells it has been suggested that fiberglass rods be used. Fiberglass rods con-sist of a thermosetting resin, either a polyester type resin or an epoxy type resin and reinforcing fiber materials. Ihe most often used fiher reinforcing material is continuous. lengths of glass fibers since they provide high strength at a relatively low cost. Other fiber such as graphite or boron could also be used but their high cost results in a relatively high priced sucker rod. Fiber reinforced plastic sucker rods are normally formed by extruding a continuous length of the fiber fila-ment reinforcing material impregnated with a suitable thermosetting resin.m e rods are made in relatively long lengths and then trimmed to the desired overall length and provided with threaded end fittings that are normally attached to the rod by an adhesive. The end fittings are made , ~
~Z~654
.
Background of the Invention m e present invention relates to the production of crude oil wherein beam pumping units are used to actuate downhole pumps to lift the crude to the surface. Sucker rods are used to couple the beam pump-ing unit at the surface to the reciprocating pump located at the bottomof the well. Sucker rods are conventionally provided with male threads at each end and are coupled together by coupling units to form a con-tinuous rod from the surface to the bottom of the well. Normally, the sucker rods are made of steel and provided with suitable threaded ends and flat sections to permit the use of wrenches in coupling the rods together. While steel rods are satisfactory, in some installations it would be desirable to use rods formed from non-corroding materials. This is especially the case when producing wells that contain sour crude, that is, crude having a high sulfur content that corrodes the rods and increases the maintenance required for the pumping unit.
In order to overcome the problem of corrosion in sour wells it has been suggested that fiberglass rods be used. Fiberglass rods con-sist of a thermosetting resin, either a polyester type resin or an epoxy type resin and reinforcing fiber materials. Ihe most often used fiher reinforcing material is continuous. lengths of glass fibers since they provide high strength at a relatively low cost. Other fiber such as graphite or boron could also be used but their high cost results in a relatively high priced sucker rod. Fiber reinforced plastic sucker rods are normally formed by extruding a continuous length of the fiber fila-ment reinforcing material impregnated with a suitable thermosetting resin.m e rods are made in relatively long lengths and then trimmed to the desired overall length and provided with threaded end fittings that are normally attached to the rod by an adhesive. The end fittings are made , ~
~Z~654
- 2 - 63293-2532 from steel or similar metals to withstand the wear of making up the rod string and disassembling it. The adhesive is normally epoxy and after the epoxy has cured, the rods are test pulled to scme preset limit, normally one-half their ultimate strength, to ensure that the threaded ends are firmly attached to the rod. In tne past the sole criteria for these tests has been either the rod failed if the end separated from the rod, or it passed the test. No attempt was made to evaluate the quality of the rod or the integrity of the joint between the end fitting and the rod body. This resulted in a large number of fiber reinforced resin type rods passing the initial test, yet failing in service by pulling off the end fitting or failure of the fiber reinforced plastic laminate itself.
Summary of the Invention The present invention solves the above problems by providing a testing procedure that accurately evaluates the overall quality of the rod, even though the rod may pass the previously used test.
The invention provides a method for testing a fiberglass sucker rod comprising: applying a tension load to the ends of the rod; measuring the applied load and elongation of the rod; plot-ting the lQ~d versus elongation; calculating from the load and elongation measurements the modulus of elasticity for at least two different load ranges; and determining the differences in the calculated modulus of elasticity for the various load ranges to determine the quality of the rod.
In practice the rod is pulled in tension to approximately one-half of its ultimate strength while measuring the load, elongation and acoustic emissions from ~he rod. The measurements ~Y
':
i249654 - 2a - 63293-2532 are controlled by a monitoring system which may be controlled by a properly programmed small computer. ~he monitoring system samples the load on the rod and its elongation several times a second while accumulating a total count of the acoustic emissions from the rod.
During the test, the acoustic emissions are caused by individual fiberglass strands breaking within the rod as the load on the rod is increased and provides a measurement of the quality of the rod laminate. From the measured load and elongation data the modulus of elasticity of the rod is calculated over two different load ranges and the difference between the two calculated values is related to the quality of the rod. Any difference in the modulus elasticity is caused either by the epoxy used to attach the metal end fittings to the rod or by a ~. P
i2~5
Summary of the Invention The present invention solves the above problems by providing a testing procedure that accurately evaluates the overall quality of the rod, even though the rod may pass the previously used test.
The invention provides a method for testing a fiberglass sucker rod comprising: applying a tension load to the ends of the rod; measuring the applied load and elongation of the rod; plot-ting the lQ~d versus elongation; calculating from the load and elongation measurements the modulus of elasticity for at least two different load ranges; and determining the differences in the calculated modulus of elasticity for the various load ranges to determine the quality of the rod.
In practice the rod is pulled in tension to approximately one-half of its ultimate strength while measuring the load, elongation and acoustic emissions from ~he rod. The measurements ~Y
':
i249654 - 2a - 63293-2532 are controlled by a monitoring system which may be controlled by a properly programmed small computer. ~he monitoring system samples the load on the rod and its elongation several times a second while accumulating a total count of the acoustic emissions from the rod.
During the test, the acoustic emissions are caused by individual fiberglass strands breaking within the rod as the load on the rod is increased and provides a measurement of the quality of the rod laminate. From the measured load and elongation data the modulus of elasticity of the rod is calculated over two different load ranges and the difference between the two calculated values is related to the quality of the rod. Any difference in the modulus elasticity is caused either by the epoxy used to attach the metal end fittings to the rod or by a ~. P
i2~5
3.
slipping of the metal end fitting on the rod. In either case, it is an indication that the rod end will probably fail in service and the rod should be rejected or discarded.
Brief Description of the Drawings ~he present invention will be more easily understood from the following description of a preferred embodiment when taken in con-junction with the attached drawings in which:
Figure 1 is a block diagram of equipment suitable for making the required measurements on a sucker rod.
Figure 2 is a plot of the load versus elongation for an actual rod.
Figure 3 is a similar plot for a second rod.
Description of the Preferred Embodiments Referrlng now to Figure 1 there is shown a block diagram of the system suitable for acquiring the data necessary for determining the q~ ty of a fiberglass sucker rod. In particular, there is shown a fiberglass sucker rod having metal end fittings 11 secured to each end.
m e metal end fittings conprise a threaded portion and a square portion 13 that can be used as a wrench flat to hold the rods as they are joined together by the threaded couplings. The metal ends are attached to the rod by an epoxy resin which is allowed to cure to firmly anchor the metal end fittings to the rods. Various means may be used to increase the bond between the metal end fittings and the rods~ for example, under-cut sections in the metal end fittings assist in anchoring the ends to the rods.
After the epoxy has been cured so that the end fittings are firmly attached to the rod, it is placed in a suitable tensile testing machine. Various types of testing machines are available commerci~lly which will apply a tensile load to a rod-like member while measuring both the load applied and the elongation of the member under test.
124~654
slipping of the metal end fitting on the rod. In either case, it is an indication that the rod end will probably fail in service and the rod should be rejected or discarded.
Brief Description of the Drawings ~he present invention will be more easily understood from the following description of a preferred embodiment when taken in con-junction with the attached drawings in which:
Figure 1 is a block diagram of equipment suitable for making the required measurements on a sucker rod.
Figure 2 is a plot of the load versus elongation for an actual rod.
Figure 3 is a similar plot for a second rod.
Description of the Preferred Embodiments Referrlng now to Figure 1 there is shown a block diagram of the system suitable for acquiring the data necessary for determining the q~ ty of a fiberglass sucker rod. In particular, there is shown a fiberglass sucker rod having metal end fittings 11 secured to each end.
m e metal end fittings conprise a threaded portion and a square portion 13 that can be used as a wrench flat to hold the rods as they are joined together by the threaded couplings. The metal ends are attached to the rod by an epoxy resin which is allowed to cure to firmly anchor the metal end fittings to the rods. Various means may be used to increase the bond between the metal end fittings and the rods~ for example, under-cut sections in the metal end fittings assist in anchoring the ends to the rods.
After the epoxy has been cured so that the end fittings are firmly attached to the rod, it is placed in a suitable tensile testing machine. Various types of testing machines are available commerci~lly which will apply a tensile load to a rod-like member while measuring both the load applied and the elongation of the member under test.
124~654
4.
Further, these machines can be controlled so that the load is applied at a constant rate, which rate can be varied if one so desires.
An acoustic transducer 20 is coupled to the rod by a suitable means to measure the acoustic emissions from the rod. The transducer may comprise a piezoelectric crystal type transducer such as a micro-phone coupled by suitable material and firmly clamped to the rod. Also, a transducer 21 is used to measure the load applied to the rod and a transducer 22 to measure the elongation of the rod as the loads are coupled to the rod. Normally, the load and elongation transducers will be part of the testing equipment and need not be separately attached to the rod. The data measured by the transducers is sampled by a data acquisition system 23 which is controlled by controller 24. The con-troller 24 may c Q rise a conventional smPll computer that is progra~med to signal each of the transducers when it is desired to make a measure-ment. The measurements made by the transducers are recorded in the com-puter memory using the data acquisition system and may be displayed on a CRT screen. miS display may then be printed on a digital printer/
plotter 31 connected to the computer.
Referring to Figures 2 and 3 there is shown representative examples of the data recorded in the computer and printed using printer/
plotter 31 while testing actual sucker rods. In particular, the data displayed is the load applied to the rod versus elor4~a~iorl, w~le ~le total acoustic counts are indicated by the numbers alongside the load/
elongation curves. me modulus of elasticity is calculated for the data shown in Figure 2 for two load ranges; the first 10-30,000 lbs. and the second 30-35,948 lbs., the ultimate load to which the rod is subject.
The first load range provided a modulus of 6.770 106 psi while the second provided a modulus of 6.671 106 psi. The difference between the two readings was 1.48 percent which is well within the acceptable range for 3o the rod. Also, as shown in Figure 2, the total counts of acoustic occur-rences is 831 which, while high, is within the acceptable range. In contrast, the modulus of elasticity in Figure 3 when calculated over the lZ~9~i~4
Further, these machines can be controlled so that the load is applied at a constant rate, which rate can be varied if one so desires.
An acoustic transducer 20 is coupled to the rod by a suitable means to measure the acoustic emissions from the rod. The transducer may comprise a piezoelectric crystal type transducer such as a micro-phone coupled by suitable material and firmly clamped to the rod. Also, a transducer 21 is used to measure the load applied to the rod and a transducer 22 to measure the elongation of the rod as the loads are coupled to the rod. Normally, the load and elongation transducers will be part of the testing equipment and need not be separately attached to the rod. The data measured by the transducers is sampled by a data acquisition system 23 which is controlled by controller 24. The con-troller 24 may c Q rise a conventional smPll computer that is progra~med to signal each of the transducers when it is desired to make a measure-ment. The measurements made by the transducers are recorded in the com-puter memory using the data acquisition system and may be displayed on a CRT screen. miS display may then be printed on a digital printer/
plotter 31 connected to the computer.
Referring to Figures 2 and 3 there is shown representative examples of the data recorded in the computer and printed using printer/
plotter 31 while testing actual sucker rods. In particular, the data displayed is the load applied to the rod versus elor4~a~iorl, w~le ~le total acoustic counts are indicated by the numbers alongside the load/
elongation curves. me modulus of elasticity is calculated for the data shown in Figure 2 for two load ranges; the first 10-30,000 lbs. and the second 30-35,948 lbs., the ultimate load to which the rod is subject.
The first load range provided a modulus of 6.770 106 psi while the second provided a modulus of 6.671 106 psi. The difference between the two readings was 1.48 percent which is well within the acceptable range for 3o the rod. Also, as shown in Figure 2, the total counts of acoustic occur-rences is 831 which, while high, is within the acceptable range. In contrast, the modulus of elasticity in Figure 3 when calculated over the lZ~9~i~4
5.
same relative load ranges provided readings of 6.69 1O6 psi and
same relative load ranges provided readings of 6.69 1O6 psi and
6.042 106 psi for a percentage difference of 7.07 percent. This is too high and the rod should be rejected even though the count of acoustic occurrences is a very low 64. The change in the dulus of elasticity over the two load ranges indicates that the end fittings are not pro-perly attached to the rod and the rod will probably fail in service by the failure of the end ~ittings.
The numbers given for acoustical counts and actual change of modulus of elasticity are good only for one particular rod system manufactured by one company. Other rods and manufacturers will have different numbers that must be arrived at by measuring a sufficient number of rods to define a statistical distribution of the information.
The numbers given for acoustical counts and actual change of modulus of elasticity are good only for one particular rod system manufactured by one company. Other rods and manufacturers will have different numbers that must be arrived at by measuring a sufficient number of rods to define a statistical distribution of the information.
Claims (3)
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for testing a fiberglass sucker rod comprising:
applying a tension load to the ends of the rod;
measuring the applied load and elongation of the rod;
plotting the load versus elongation;
calculating from the load and elongation measurements the modulus of elasticity for at least two different load ranges;
and determining the differences in the calculated modulus of elasticity for the various load ranges to determine the quality of the rod.
applying a tension load to the ends of the rod;
measuring the applied load and elongation of the rod;
plotting the load versus elongation;
calculating from the load and elongation measurements the modulus of elasticity for at least two different load ranges;
and determining the differences in the calculated modulus of elasticity for the various load ranges to determine the quality of the rod.
2. The method of Claim 1 wherein the difference between the calculated modulus of elasticity is less than five percent for an acceptable rod.
3. A method for testing fiberglass sucker rods comprising:
applying a tension load to the ends of the rod, said tension load increasing at a present rate;
measuring the load applied and the elongation as said tension load increases;
calculating the modulus of elasticity from said load and elongation measurements for at least two different load ranges;
and determining the difference between said two calculated values of the modulus of elasticity and rejecting all rods where the difference exceeds a present value.
applying a tension load to the ends of the rod, said tension load increasing at a present rate;
measuring the load applied and the elongation as said tension load increases;
calculating the modulus of elasticity from said load and elongation measurements for at least two different load ranges;
and determining the difference between said two calculated values of the modulus of elasticity and rejecting all rods where the difference exceeds a present value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US61950884A | 1984-06-11 | 1984-06-11 | |
| US619,508 | 1984-06-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1249654A true CA1249654A (en) | 1989-01-31 |
Family
ID=24482199
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000483527A Expired CA1249654A (en) | 1984-06-11 | 1985-06-10 | Quality control for sucker rods |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1249654A (en) |
-
1985
- 1985-06-10 CA CA000483527A patent/CA1249654A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |