Development of ultra-high strength seamless G. Gomez, S. Cravero, M. Bellingardi
INTRODUCTION Pipe for Perforating Gun Carriers (PG) need to sustain during field operation high external hydrostatic pressures and high internal shock loads. Increase demand of higher strength to sustain higher collapse loading derive in the need of pipes with Specified Minimum Yield Strength (SMYS) of 165ksi and above. Typical P110 Tubing: 19800psi Typical 135ksi Gun Carrier: 24300psi Outer 165ksi Diameter: Gun Carrier: 3.125 79.375mm 29700psi 175ksi Nominal Outer Diameter: Gun Wall: Carrier: 0.3125 3.125 7.938mm 79.375mm 31500psi Tensile Nominal Outer Diameter: Strength: Wall: 0.3125 3.125 1350 kn 7.938mm 79.375mm Outer Tensile Nominal Diameter: Strength: Collapse: Wall: 0.3125 3.125 1660 19800psi kn 7.938mm 79.375mm Nominal Tensile Strength: Wall: Collapse: 0.3125 2025 24300psi kn 7.938mm Tensile Nominal Strength: Collapse: 2148 29700psi kn Nominal Collapse: 31500psi 2
INTRODUCTION Based on these requirements, steel seamless pipes with good impact toughness and strict dimensional tolerance are required. The development of such high strength materials with good toughness is a challenge Steel chemistry and processing conditions have to be carefully designed and optimized to achieve these strict requirements. 3
AGENDA Design of steel chemistries for 165ksi and 175ksi based on model calculations. Validation with industrial data and fine tuning processing conditions. Characterization of materials resulting from industrial trials (microstructure, tempering curve, hardness, tensile and fracture toughness properties). 4
OBJECTIVE To develop 165ksi and 175ksi grades with adequate fracture toughness resistance. Yield Strength YS (ksi) Ultimate Tensile Strength UTS (ksi) Elongation (% ) Impact Toughness Charpy-V Notch CVN (J) Full size specimen 165ksi 165-187 > 170 > 12 > 76 175ksi 175-197 > 180 > 11 > 44 * Test at Room Temperature, Longitudinal Orientation Metallurgical challenges: To meet toughness requirements in this ultra-high strength steels. Tempering temperature should be above 450 C to allow for hot straightening operation without introducing residual stresses. 5
TEMPERING MODEL Model developed at R&D to describe the martensite hardness reduction during tempering. Yield Strength (YS) and Ultimate Tensile Strength (UTS) are derived from hardness prediction, based on empirical relations adjusted for steels. Inputs: Steel chemistry As quenched hardness Thermal cycle: isothermal treatment or user introduced tempering curve (for example a curve calculated with the furnace thermal model). Outputs: Hardness, YS and UTS. 6
TEMPERING MODEL A time-temperature equivalent parameter P is used to characterize the tempering curve: T time Integral version of the Hollomon-Jaffe parameter: P( T, t) t 0 exp Q R T dt The activation energy Q depends on steel chemistry A mathematical function is used to describe softening during tempering: 2 w H( P) H 0 min 2 2 log( P) log( P ) w H H H (V, ) 0 P max 7
PERFORATING GUN YS > 165 ksi Strength (ksi) According to the tempering model and experimental tests, CrMo1 steel used for a 155ksi gun carrier can reach 165 ksi min YS, but tempering temperature is very close to the minimum specified. 220 Steel Tempering model CrMo1 500 C* *calculations aiming at YS = 170 ksi performed with tempering model (10-15 minutes soaking time) 210 200 190 180 170 160 150 140 130 120 110 Experimental: YS UTS Model: YS UTS 100 250 300 350 400 450 500 550 600 650 700 750 8 Tempering temperature ( C)
CVN at RT * (Joules) PERFORATING GUN YS > 165 ksi Industrial results for CrMo1 steel: 110 105 100 95 90 85 80 CrMo1 HT1 HT2 75 70 150 155 160 165 170 175 180 185 190 Yield Strength (ksi) A modified Heat Treatment (HT) process (HT2) was developed to improve strengthtoughness ratio on CrMo1 steel, playing with steel grain refinement. CrMo1 steel with HT2 fulfilled 165ksi specification and final tempering temperature was about 500 C. 9
PERFORATING GUN YS > 175 ksi Several chemistries were analyzed with the tempering model. Some examples are shown below: Steel CrMo1 CrMo2 CrMo3 C (%) 100 100 110 Mn (%) 100 110 110 Si (%) 100 100 100 Cr (%) 100 120 150 Mo (%) 100 140 100 Al (%) 100 100 150 Tempering model 440 C 460 C* 525 C* *calculations for single treatment aiming at YS = 180 ksi (10-20 min soaking). According to these calculations CrMo2 and CrMo3 were suitable chemistries to produce 175ksi. 1 0
CVN at RT * (Joules) CVN at RT * (Joules) PERFORATING GUN YS > 175 ksi Industrial trial results for CrMo2 and CrMo3: 100 100 90 90 80 80 70 70 60 50 CrMo2 HT1 HT2 60 50 CrMo3 Aust 1 Aust 2 Aust 3 40 170 175 180 185 190 195 YS (ksi) 40 170 175 180 185 190 YS (ksi) CrMo3 presented slightly better combination of strength-toughness than CrMo2. In both HT2 improved mechanical properties through grain refinement. In CrMo3 steel the modification of austenitization temperature was also useful to improve grain size. 11
TECHNOLOGICAL TEST FOR PERF GUNS MATERIAL Charpy-V Notch Impact values for both 165ksi and 175ksi grades were satisfactorily above minimum requirement Nevertheless, especially for small size guns, charpy test in the transversal direction may be difficult or impossible to be performed, Furthermore, Charpy-V Notch Impact test results may be not be truly representing the material behavior in dynamic conditions 12
TECHNOLOGICAL TEST FOR PERF GUNS MATERIAL developed a burst test in pipes with a longitudinal stress concentrator as a way to rank the fracture toughness resistance among different steels. Longitudinal defect Transverse Charpy (equivalent to transverse Charpy orientation) Longitudinal Charpy 13
TECHNOLOGICAL TEST FOR PERF GUNS MATERIAL Burst test of Perf Gun material with a longitudinal defect. - Defect length equal to the scallop diameter (25mm) - Defect mechanized by Electron Discharge Method (EDM), it must be thinner than 1mm - Temperature: Room temperature (RT). - Loading Rate: lower than 30 MPa/s The material must complain with: Minimum pressure requirements Minimum defect opening / final crack length 14
TECHNOLOGICAL TEST FOR PERF GUNS MATERIAL Significant differences were found between good and bad materials: - Good materials: short final crack and high crack mouth opening displacement - Bad materials: long final crack and low Crack Mouth Opening Displacement (CMOD) 15
TECHNOLOGICAL TEST FOR PERF GUNS MATERIAL - GOOD Material: High CMOD / final Crack Length ratio 16
TECHNOLOGICAL TEST FOR PERF GUNS MATERIAL - BAD Material: High CMOD / final Crack Length ratio 17
Final mouth/length TECHNOLOGICAL TEST FOR PERF GUNS MATERIAL Comparison between High-Strength grades (135/145ksi) and Ultra-High Strength grades (165/175ksi) 0,450 0,400 0,350 PG135/PG145 PG165 PG135/PG145 M1 25 - OD4,5" M2 25 - OD4,5" 0,300 M6 25 - OD2" M7 25 - OD4,5" 0,250 0,200 PG175 M11 25 - OD2" M12 25 - OD4,5" M13 25 - OD4,5" 0,150 0,100 M14 25 - OD4,5" M15 25 - OD4,5" 0,050 0,000 0 5 10 15 20 Material/Sample Bad material made on purpose 18
CONCLUSIONS HT Model calculations helped to design steel chemistries and to make first setting for tempering conditions, to achieve 165ksi and 175ksi min YS Mill runs confirmed the targeted tensile-impact properties windows were met, using adequate HT process and matching the required minimum tempering temperatures A technological test to evaluate in a simple way the capability of the material to sustain high impact loading was developed. In terms of Crack Opening vs. Crack length, the developed 165/175ksi grades are behaving in the same way as the consolidated 135/45ksi grades. 165ksi and 175ksi grades have been successfully qualified with field explosive tests (survivability tests) and are now available in the industry 19
Thank you! Questions? Development of ultra-high strength seamless