Sucker Rod Pumping Workshop Wyndham Hotel, Houston, Texas September 11 – 14, 2007 Lubricant Selection Using Circumferential Displacement of Sucker Rods Erik Tietz, P.E. Arun Sriraman UPCO, Inc.
Goals of this project • Phase 1 - Testing of lubricants. • Phase 2 - Verifying and reestablishing the API displacement values for D & HS grade sucker rods. • Phase 3 – Analyzing the effect of applying lubricant on the face of coupling and sucker rod. • Phase 4 – Studying the decay that might happen after the rod has been used on multiple occasions. 2007 Sucker Rod Pumping Workshop 2 Sept. 11 - 14, 2007
Summary Synopsis of the paper 1) Why did UPCO decide to take on the testing of displacement? What are our goals? 2) Core Engineering concepts involved in this project. 3) The displacement testing. 4) What was measured during the test? 5) The eight critical parameters 6) The results of UPCO displacement testing. 2007 Sucker Rod Pumping Workshop 3 Sept. 11 - 14, 2007
1. Why did UPCO perform this project? • Customer feedback indicated failures due to lack of, loss of and over displacement. • As a result of this, there were numerous questions which we at UPCO could not answer with adequate proof. • Some of the questions which were raised and led us into this project are as follows: – Were displacement values correct? – What affected these values? – What type of lubricant is the correct choice for sucker rod – coupling make up? 2007 Sucker Rod Pumping Workshop 4 Sept. 11 - 14, 2007
2. Core Engineering concepts involved in this project The core engineering concepts used in this project are as follows: A. Forces acting on a sucker rod coupling make up B. Circumferential displacement C. Stress D. Strain (Shear & Normal Strain) E. Modulus of Elasticity 2007 Sucker Rod Pumping Workshop 5 Sept. 11 - 14, 2007
Forces acting in a sucker rod coupling make up A A B A Normal Forces acting in a direction parallel to the axis of the rod body. Normal forces are a very desirable attribute in a sucker rod coupling make up process B Shear forces acting on the pin which is a detrimental attribute in a sucker rod coupling make up process. 2007 Sucker Rod Pumping Workshop 6 Sept. 11 - 14, 2007
Circumferential Displacement Circumferential displacement: API states that circumferential displacement is the distance measured after makeup, between the displaced parts of a vertical line scribed across the external surfaces of the box and pin when they are in a shouldered hand tight relationship prior to makeup. Hand tight level (No displacement) UPCO Minimum Displacement value UPCO Maximum Displacement value 2007 Sucker Rod Pumping Workshop 7 Sept. 11 - 14, 2007
Stress • What is Stress? Stress is the load applied per unit area of cross section. There are 2 types of stress, namely normal and shear stress. • Stress = Load / Area of cross section • Example: The area of cross section for a ¾” sucker rod is 0.44 Sq.In • Units: PSI (Pounds per square inch) 2007 Sucker Rod Pumping Workshop 8 Sept. 11 - 14, 2007
Strain Strain • Strain is the elongation of the specimen when it is subjected to a load. • In our case, it will be the stretch of the sucker rod pin during the process of make up. • Two types strain – Normal and Shear • Shear & Normal Strain can be measured by strain gauges. 2007 Sucker Rod Pumping Workshop 9 Sept. 11 - 14, 2007
Strain Gauge • The pictures depicted below show examples of shear and normal strain gauges (both positive and negative). Normal Shear 2007 Sucker Rod Pumping Workshop 10 Sept. 11 - 14, 2007
Modulus of Elasticity (MOE) • MOE = Stress / Strain (Elastic region of the curve) • Units = PSI Plastic Region Elastic Region 2007 Sucker Rod Pumping Workshop 11 Sept. 11 - 14, 2007
3. Displacement testing The test • The overall test can be broken down to four sub tests a) Subtest 1: Testing of new rod and new coupling with new rod displacement values (maximum and minimum). b) Subtest 2: Testing of old rod and new coupling with re-run displacement values (maximum and minimum). c) Subtest 3: Testing of old rod and old coupling with re-run displacement values (maximum and minimum). d) Subtest 4: Testing of old rod and old coupling with re-run displacement values (maximum and minimum). Note: In subtest 4, after hitting the maximum mark and then relieved, the rod is made up until failure. 2007 Sucker Rod Pumping Workshop 12 Sept. 11 - 14, 2007
Displacement Testing Machine (DTM) Displacement testing machine – A brief overview • The machine can produce sufficient amount of torque to shear a 1 1/8 ” sucker rod pin. • The gear ratio is slow enough to perform a test in 30 seconds. • It has a 1 HP DC drive with variable drive capability. • The machine is coupled with a data acquisition system which has the capability to sample 10000 data points per second. 2007 Sucker Rod Pumping Workshop 13 Sept. 11 - 14, 2007
Displacement Testing Machine (DTM) A pictorial explanation of the DTM 2007 Sucker Rod Pumping Workshop 14 Sept. 11 - 14, 2007
Samples for testing Samples for testing • A total of 13 test were conducted. 12 lubricant tests and one no lube test. • The lubricant was applied only on the threads of the sucker rod. No lube on the faces. • All sucker rod samples were ¾” CD with the same heat number. • All couplings were ¾” full size with same heat number. 2007 Sucker Rod Pumping Workshop 15 Sept. 11 - 14, 2007
4. What was measured directly from the test? • The three main measurements needed for this project were – Torque applied – Shear Strain – Normal Strain • The torque applied (positive & negative) during the displacement process was measured using a load cell with a 12” moment arm. Load cell set up with a 12” moment arm for measuring the torque 2007 Sucker Rod Pumping Workshop 16 Sept. 11 - 14, 2007
5. The eight critical parameters 1. Average Maximum Torque 2. Total Energy Absorbed 3. Overall minimum % of design yield 4. Overall maximum % of design yield 5. Overall maximum % of actual shear 6. Overall difference index with torque 7. Overall difference index without torque 8. Overall relief index 2007 Sucker Rod Pumping Workshop 17 Sept. 11 - 14, 2007
Sample graph with data Normal force curve Shear force curve Torque curve 2007 Sucker Rod Pumping Workshop 18 Sept. 11 - 14, 2007
Average Maximum Torque • This is the average maximum torque of all four tests on one sample. • The final result is the average for all samples of one type of lubricant. • The average maximum torque was rated as the smallest value being the best and the largest value being the worst. • Units: ft-lb 2007 Sucker Rod Pumping Workshop 19 Sept. 11 - 14, 2007
Average Maximum Torque Average Maximum Torque 2007 Sucker Rod Pumping Workshop 20 Sept. 11 - 14, 2007
Average Maximum Torque – Results Table 2007 Sucker Rod Pumping Workshop 21 Sept. 11 - 14, 2007
Total amount of energy absorbed • This is the total amount of energy absorbed for all four tests on one sample. • This value includes the energy required for maximum displacement and it also includes the energy to break the joint for all four tests. • The total amount of energy absorbed was rated as the smallest value being the best and the largest value being the worst. • Units: ft-lb 2007 Sucker Rod Pumping Workshop 22 Sept. 11 - 14, 2007
Total amount of energy absorbed Total amount of energy absorbed = Difference in the numerical values between the two discrete points 2007 Sucker Rod Pumping Workshop 23 Sept. 11 - 14, 2007
Total amount of energy absorbed – Results Table 2007 Sucker Rod Pumping Workshop 24 Sept. 11 - 14, 2007
Overall Minimum % of Design Yield • This is the average normal stress in the stress relief at the minimum displacement divided by API design stress (85000 PSI). • The overall minimum % of design yield was rated as the smallest value being the worst and the largest value being the best. Note: Values above 100 % are unacceptable. • Units: % 2007 Sucker Rod Pumping Workshop 25 Sept. 11 - 14, 2007
Overall Minimum % of Design Yield Maximum value indicated in the region of the curve / 85000 PSI 2007 Sucker Rod Pumping Workshop 26 Sept. 11 - 14, 2007
Overall Minimum % of Design Yield 2007 Sucker Rod Pumping Workshop 27 Sept. 11 - 14, 2007
Overall Maximum % of Design Yield • This is the average normal stress in the stress relief at the maximum displacement divided by API design stress (85000 PSI). • The overall maximum % of design yield was rated as the smallest value being the worst and the largest value being the best. Note: Values above 100 % are unacceptable. • Units: % 2007 Sucker Rod Pumping Workshop 28 Sept. 11 - 14, 2007
Overall Maximum % of Design Yield Maximum value indicated in the region of the curve / 85000 PSI 2007 Sucker Rod Pumping Workshop 29 Sept. 11 - 14, 2007
Overall Maximum % of Design Yield 2007 Sucker Rod Pumping Workshop 30 Sept. 11 - 14, 2007
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