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Suction Roll Material Comparison

Suction Roll Material Comparison

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Suction Roll Material Comparison

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  1. Suction RollMaterial Comparison 11th International Symposium on Corrosion in the Pulp & Paper Industries Paul E Glogowski Metso Paper Aiken, SC

  2. Nine Principal Material Features 1 Microstructure 2 Chemical composition 3 Mechanical properties 4 Corrosion resistance 5 Corrosion fatigue 6 Residual stress 7 Threshold fatigue crack growth 8 Thermal Fatigue Resistance 9 Experience

  3. Slab ready Refining in CLU-converter Melting in electric arc furnace Continuous casting to slab Slab heating Hot Rolling to plate Hot Rolled Plate Inspection 39831-90

  4. Shell Blank Cutting inc. test piece Hot preforming Hot forming Joint preparation and welding of circumferential welds (SAW) Joint preparation and ES-welding of longitudinal weld Hot Forming Heat treatment 100% NDT of welds (x-ray or isotope)

  5. Melting in electric arc furnace Refining in AOD-converter Centrifugal casting into rotating mold Heat treatment Taking the shell out of mold Solidification and cooling in rotating mold Inside and outsidemachining Centrifugal Casting

  6. Microstructure

  7. Chemical Composition

  8. Chemical Composition

  9. Mechanical Properties

  10. Electrochemical Corrosion Scan in typical newsprint whitewater Potential, volts 0 • Ecorr Log Current, amps (corrosion rate) Pitting Electrochemistry Environment pH = 4.5 Cl- = 100 ppm Thiosulfate ion (S2O3=) = 40 ppm Temperature = 140°F (60°C) Conductivity = 4000 microsiemens • Ecorr is the corrosion potential about -450 millivolts (MV) • In the example on the left, 3RE60 is placed in the above environment and the potential is measured compared to a standard electrode (H)

  11. Electrochemical Corrosion Scan in typical newsprint whitewater Epit Erepassivate Margin of Safety 0 Potential, volts • Ecorr Log Current, amps (corrosion rate) Pitting Electrochemistry Electrochemical Corrosion Scan in typical newsprint whitewater • For suction roll alloys, many manufacturers report the margin of safety (MS) for the stainless steel. • For our example, we have a pitting MS of 1250 mV or 1.25 volts. • A more conservative MS would be the pit repassivation which is 1150 mV or 1.15 volts for this example. 0 • Ecorr

  12. Electrochemical Corrosion Test Results

  13. Corrosion Fatigue Strength • Alloy tensile strength • Microstructure • Environment • Frequency

  14. Corrosion Fatigue StrengthTest Methods • Tatnal-krause reverse plate bending • A drilled hole to simulate the stress concentration from suction roll drilled holes (KT = 2) • R.R. Moore rotating bending • A better simulation of a suction roll. Stress concentrations can be increased by notching the specimen

  15. Corrosion Fatigue -LOW pH -CHLORIDES -SULPHUR COMPOUNDS -HIGH TEMPERATURE -POOR ROLL CLEANING -CHEMICALS AND DETERGENTS -FEQUENCY LAB FASTER THAN MACHINE -DIFFERENCE BETWEEN LAB TESTS AND ACTUAL CONDITION S T R E S S -RESIDUAL STRESS -THERMAL STRESSES -ABNORMAL LOADS -DEFECTS IN SHELL CALCULATED OPERATING STRESS LEVEL 9 10 C Y C L E S

  16. Published Corrosion Fatigue Strengths Estimated at 1 Billion cycles

  17. Residual Stress • Sach’s test • Destructive • expensive • For ID measurement gages are mounted on OD and sample is incrementally bored • For OD measurement strain gages are mounted on ID and sample is incrementally turned

  18. Sach’s Residual Stress Calculations Equations for longitudinal and circumferential stresses: turning • nL = - E/1-2 [(n-N/2)(n+1 - n-1+n] • nC = - E/1-2 [(n-N/2)( n+1 - n-1+ (n+N/2n) n] boring • nL = - E/1-2 [(n-N/2)( n+1 - n-1+(n+N/2n) n] • nC = - E/1-2 [(n-N/2)( n+1 - n-1+ n}

  19. Residual StressAs a Function of Heat Treatment

  20. Turning Sample Boring Sample Strain gage Strain gage Strain gage Strain gage Strain gage Strain gage Strain gage Strain gage Strain gage Strain gage

  21. Comparison of Residual Stressto Ultimate Tensile Strength

  22. Typical Stages of Fatigue

  23. Threshold Fatigue Crack Growth DEFINITIONS • DK = The driving force or stress intensity factor • DK is a scale factor which defines the magnitude of the stress field at the crack tip • Crack growth rate, da/dn = The amount of crack growth per load cycle

  24. Threshold Fatigue Crack Growth • Driving force for crack (or flaw) growth • Instantaneous length of crack at any time, t • Geometry of cracked material • The magnitude of cyclic loading • Dkthreshold = Ds(acritical *)1/2 Where: Ds = range of cyclic stress acritical = 1/2 the critical flaw size required for fatigue crack growth

  25. Threshold Fatigue Crack GrowthTest Environments

  26. P a W P B Threshold Fatigue Crack Growth K = [P/B(W1/2)] [(2+)/(1-)3/2 ] (0.866+4.64-13.322 + 14.723 - 5.64) where: P is the range of load  is the crack length B is the specimen thickness W is the specimen width

  27. C L Threshold Fatigue Crack Growth Specimen Orientation

  28. Threshold Fatigue Crack Growth

  29. Threshold Fatigue Crack Growth

  30. Critical Flaw Size

  31. Critical Flaw Size(cyclic stress range 55 MPa, 8000 psi)

  32. Critical StressRequired for Crack Growth

  33. Threshold Fatigue Crack GrowthCritical Stress for a 2.54 mm edge flaw

  34. Threshold Fatigue Crack Growth NOTE: The stress intensity factor, K, allows one to Correlate between the behavior of a cracking lab Specimen and a cracked component because it Characterizes the stress field at the crack tip

  35. Conclusions • Microstructure • A fine and homogeneous microstructure, give improved strength and corrosion fatigue strength. • Chemical composition • Duplex stainless steels have similar alloying elements Adding molybdenum provides improved corrosion resistance, including crevice and chloride pitting attack. • Corrosion fatigue strength • Higher strength and higher corrosion resistance leads to higher corrosion fatigue strength.

  36. Conclusions • Threshold fatigue crack growth • High threshold fatigue crack growth rate values contribute to long lived suction roll shells. • Thermal fatigue strength • Smaller grain size gives better resistance to thermal fatigue. • Experience • Design and application of suction rolls requires experience and machine operating tim eto prove an alloy

  37. Conclusions • Material A has the suction roll shell properties and the experience to handle all paper making suction roll applications.

  38. Thank You