Comparison of the Mechanical Properties of Steel and Ductile Iron Pipe Materials

Transcription

1 Comparison of the Mechanical Properties of Steel and Ductile Iron Pipe Materials NC AWWA WEA November 14, 2017 Rich Mielke, P.E. Director of Engineering

2 Comparison of the Mechanical Properties of Steel and Ductile Iron Pipe Materials Brent Keil, PE Corp. Chief Engineer, Northwest Pipe Co. Jack Devletian, PhD Professor, Portland State University Rich Mielke, PE Director of Engineering, Northwest Pipe Co.

3 Jack Devletian, Ph.D. B.S. Mechanical Engineering, University of Massachusetts,1963 M.S. Metallurgical Engineering, University of Wisconsin, 1966 Ph.D. Metallurgical Engineering, University of Wisconsin, 1972 Associate Professor (tenured) Youngstown State University Materials Science Department Professor Oregon Graduate Institute Materials Science & Engineering Department Research Professor Portland State University Mechanical Engineering Department

4 Introduction and Purpose Engineers today are pressured to standardize Perceived technical or commercial fairness Structural designs treated similarly despite different mechanical properties Certain aspects of performance based design are comparable

5 Introduction and Purpose Evaluation of similarities and differences in mechanical properties Two common metallic pipe products dip and steel Historical background Mechanical testing Review of AWWA design criteria Exploration of differences

6 History of Iron Iron and steel production dates to 1500BC Iron is softer than bronze By 1100BC use of carbon in iron had been discovered Reheating iron in a furnace with charcoal Carbon increases hardness of iron

7 Wrought Iron Worked History of Iron 0.02% to 0.08% carbon Wrought Iron replaced copper and bronze for weapons Beginning of the Iron Age Furnaces still not hot enough to melt Iron

8 History of Iron Blast furnace developed Blasts air through layer charcoal, flux, iron ore Molten iron poured troughs Pig Iron

9 Development of Steel Manufacturing Steel has lower carbon content Was difficult to make due to carbon Desirable due to properties Mid 1800 s Bessemer Process developed

10 Development of Steel Manufacturing Compressed air through molten Pig Iron Refined with Iron, Carbon, Manganese Reduced oxygen keeping carbon Henry Bessemer

11 Metal Classification

12 Metal Classification Current Systems Wrought Iron 0.02% to 0.08% Carbon Steel Up to 2% Carbon Cast Iron over 2%

13 Cast Iron Classification Originally grouped by fracture surface appearance White and Grey Grey is easily cast /White is extremely hard Ductile Iron (spherical or nodular) Nodules formed by adding Magnesium

14 Steel Classification Thousand of compositions Classified by chemical composition Low carbon under 0.2% Medium 0.2% to 0.5% Steel water pipe typically 0.08% to 0.2%

15 Steel Classification HSLA Uses alloying elements vs. carbon for strength Structural Grade - SS Stainless Steels High Temp Steels Improved formability for deep drawing Specific Al content, interstitial free

16 Important Mechanical Properties Yield Tensile Elongation Toughness

17 Yield Strength Approximate point where material transitions from elastic to plastic behavior Hooke s Law up to yield Stress vs. Strain line slope Modulus of Elasticity, E Yield typically measure with 0.2% offset method Used in design of Steel and Ductile Iron Pipe

18 Tensile Strength Also called Ultimate Strength Maximum stress achieved Commonly reached before fracture Can be used for some designs, but typically not used for steel or ductile iron water pipe

19 Elongation Measurement of ductility Strain related Measurement of permanent growth during tensile test Bend Test another type of ductility test

20 Toughness Measurement of materials ability to absorb energy and deform plastically Material Toughness Materials need combination of ductility and strength Charpy Test represents Relative Toughness Steel and Ductile Iron pipe use Charpy test

21 Toughness

22 AWWA Steel and DIP Properties Property Ductile Iron Pipe Steel Pipe Yield 42 ksi ksi Tensile 60 ksi ksi Elongation 10% 18 30% Impact 5 70 deg. F deg. F Bend Not required by AWWA 180 degree

23 Evaluation of Mechanical Properties Yield Strength Ultimate Tensile Strength Percent Elongation Testing Performed Charpy Impact Toughness Bend Test Micrograph Analysis

24 Micrographs Testing ASTM A247 and ASTM E112 Yield, Tensile, Elongation, Charpy, Bends ASTM A370 All tests performed on full thickness flat bars Represents actual application AWWA DIP standards require rod style test

25 DIP and CIP Samples Diameter, inches Thickness, inches Class Diameter, inches Thickness, inches Class CL CL CL CIP DIP , 42ksi Ys, 60ksi Ts, and 10% Elongation All US origin

26 Steel Pipe Samples Material Specification Diameter (Inch) Thickness (Inch) Design Operating Pressure (psi) Min. Specified Yield, (ksi) Min. Specified Tensile, (ksi) Min. Specified Elongation (%) ASTM A 1018 SS Gr ASTM A 1018 HSLA Gr ASTM A 1011 SS Gr ASTM A 1011 SS Gr

27 Ductile Iron Tensile Test Steel Tensile Test

28 Completed Bend Test Samples

29 Material Type Thickness Yield Tensile Elongation Charpy 4-40 F 0 F 30 F 65 F DIP ,766 58, DIP 43,771 55, DIP 44,865 55, DIP ,083 54, DIP 40,345 54, DIP 41,325 55, DIP ,073 58, DIP 39,772 54, DIP ,768 57, DIP Average Average 44,175 50, DIP 43, ,351 psi psi Average ,820 62, % DIP ,821 52, DIP 42,972 52, DIP ,227 53, DIP 40,868 51, DIP ,870 51, DIP 42,097 53, DIP ,060 56, DIP 45,380 54, DIP ,228 51, DIP 46,870 54, Cast Iron Pipe NA 5 23,856 NA Cast Iron Pipe NA 5 21, Steel A1018 GR ,355 67, Steel A1018 GR ,634 68, Steel A1018 GR ,205 68, Steel A1018 GR ,200 65, Steel A1018 GR ,200 65, Steel A1011 GR ,400 75, Steel A1011 GR ,300 76, Steel A1011 GR ,400 72, Steel A1011 GR ,800 72,

30 Testing Review DIP Ys, Ts and Elongation below Minimums Full Pipe wall thickness samples Pipe ID and OD were left intact Surface irregularities found in pipe wall were not removed Ductile Iron Mid Wall Ductile Iron Inside Wall

31 Testing Review DIP Tensile values match closely with DIP Handbook (6 th Edition) average burst tensile strength reported of 53,320 psi

32 Testing Review Steel test results were typical Ys, Ts, and Elongation exceed minimums

33 AWWA Design Criteria

34 AWWA Design Criteria Both DIP and Steel use the Barlow Hoop Stress Equation t = pipe wall thickness PD P = pressure, psi t = 2S D = outside pipe diameter, in S = allowable stress

35 AWWA Design Criteria Difference occurs in determining S, allowable stress AWWA M-11 uses two equations S for working is 50% of Min Ys S for max or transient is 75% of Min Ys

36 AWWA M41 AWWA Design Criteria One equation, P=working plus 100psi allowance Uses 50% Ys Shows equation with numerator and denominator multiplied by 2 giving appearance of designing to 2 times the working pressure DIP designed wall should be thicker than steel

37 AWWA Design Criteria Assume a 48-inch nominal diameter pipe that will operate at a pressure of 150 psi and may encounter a pressure during a transient condition of 250 psi. Both materials will be considered to have a minimum yield of 42,000 psi. For Steel Pipe: Operating Condition: Transient Condition: The greater of the two values is 0.198in, so that would be the minimum specified wall thickness for steel pipe. Due to the mechanical properties and consistency of the material, no additional allowances or tolerances are added to the thickness. Additional checks would be analyzed based on the conditions in which the pipe will be used such as: Handling, buckling and deflection due to earth load.

38 AWWA Design Criteria Assume a 48-inch nominal diameter pipe that will operate at a pressure of 150 psi and may encounter a pressure during a transient condition of 250 psi. Both materials will be considered to have a minimum yield of 42,000 psi. For Ductile Iron Pipe: With DIP, a service allowance of 0.08-in and the casting tolerance of 0.08-in are required, giving a minimum specified wall thickness of in. For DIP, additional checks would be analyzed based on the conditions in which the pipe will be used, such as: handling, deflection due to earth loads, ring yield strength and ring ultimate strength. It is important to note that the additional checks for the two pipe materials may look similar in the equations used, but the factors required in the calculations will be different.

39 Conclusions Steel and DI Pipe are both ferrous materials Exhibit substantially different mechanical properties Steel will typically exhibit: Elongations 2 to 4 times higher Charpy Impact Values 3 to 30 times higher Substantially higher Material Toughness Ability to pass 180degrees bend test Yield values 5 to 10ksi above specified min values

40 Conclusions DIP contains over 2% carbon and is cast DIP has better ductility compared to cast iron pipe Surface irregularities likely the cause of lower tests AWWA designs treat the two products differently AWWA designs appear appropriate for each material AWWA design philosophy should not be comingled No technical justification to do so

41 Comparison of the Mechanical Properties of Steel and Ductile Iron Pipe Materials NC AWWA WEA November 14, 2017 Rich Mielke, P.E. Director of Engineering