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Buried Natural Gas Pipelines - PowerPoint PPT Presentation

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Buried Natural Gas Pipelines

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  1. Buried Natural Gas Pipelines Natural gas is transported in buried pipelines. A challenging materials problem: what do you use to make the pipe?

  2. Buried Natural Gas Pipelines It is vital that the pipeline resist rupture or cracking. The gas is flammable, and the pipelines pass under populated areas. What type of material should be used? METAL CERAMIC POLYMER

  3. Buried Natural Gas Pipelines General materials properties: METAL - strong, tough, easily formed into tube-like shape, easy to join in a leak-tight pipe miles long, can corrode, somewhat expensive CERAMIC - very strong, brittle, more difficult to form, difficult to join, relatively low cost POLYMER - lower strength, fairly tough, easily formed, easy to join, moderate cost

  4. Buried Natural Gas Pipelines General materials properties: METAL - strong, tough, easily formed into tube-like shape, easy to join in a leak-tight pipe miles long, can corrode, somewhat expensive CERAMIC - very strong, brittle, more difficult to form, difficult to join, relatively low cost POLYMER - lower strength, fairly tough, easily formed, easy to join, moderate cost METAL has the best combination of properties.

  5. Buried Natural Gas Pipelines What kind of metal should be selected? The following would all work reasonably well. Titanium Nickel Stainless steel Copper Aluminum Lead Steel

  6. Buried Natural Gas Pipelines Now let’s look at cost. Titanium: $40/lb. Nickel: $14/lb. Stainless steel: $4/lb. Copper: $3.50/lb. Aluminum: $1.30/lb. Lead: $1.25/lb. Steel: $0.46/lb.

  7. Buried Natural Gas Pipelines Some of these are just too costly. Titanium: $40/lb. Nickel: $14/lb. Stainless steel: $4/lb. Copper: $3.50/lb. Aluminum: $1.30/lb. Lead: $1.25/lb. Steel: $0.46/lb.

  8. Buried Natural Gas Pipelines Let’s take a closer look at the less expensive metals. Titanium: $40/lb. Nickel: $14/lb. Stainless steel: $4/lb. Copper: $3.50/lb. Aluminum: $1.30/lb. Lead: $1.25/lb. Steel: $0.46/lb.

  9. Buried Natural Gas Pipelines Each one has some good and some bad features. Aluminum: $1.30/lb. - easy to form, good strength, lightweight, corrosion resistant, slightly difficult to weld Lead: $1.25/lb. - easy to form, low strength, heavy, corrosion resistant, easy to weld Steel: $0.46/lb. - easy to form, good strength, medium weight, vulnerable to rusting, easy to weld

  10. Buried Natural Gas Pipelines Steel pipe is substantially less costly and has good properties except for the possibility of rusting. If we could beat the rust problem, this looks like the best choice.

  11. Buried Natural Gas Pipelines Mg’s low emf makes it a useful sacrificial anode for buried steel pipe (e.g., natural gas lines). The Mg slowly corrodes, and the steel becomes the cathode, which does not oxidize.

  12. Ni SUPERALLOYS Since the first jet engines were developed in Germany (1938-45), engineers have recognized that the key to engine efficiency and power was a high combustion zone temperature in the jet engine. Early Nazi jet aircraft used air-cooled stainless steel turbine blades. These typically failed after 10 to 25 hours of operation. Pilots often returned from missions with one or even zero engines running. Me-262 jet-propelled aircraft could fly 11.5 km high and had a top speed of 870 kph.

  13. Ni SUPERALLOYS The compressor blades at the engine’s intake pressurize the air and feed it into the combustion chambers where it is used to burn fuel. The expanding combustion gases flow through the turbine blades and out the exhaust, providing thrust and driving the compressor blades.

  14. Ni SUPERALLOYS Both pressure and temperature rise sharply from the intake to the combustion zone. Thus, the most “difficult” materials problems for turbine designers lie in the combustion zone.

  15. REQUIREMENTS FOR COMBUSTION ZONE TURBINE BLADES AND RELATED PARTS

  16. Ni SUPERALLOYS Both compressor and combustion zone turbine blades need high specific strength (strength/density). At lower temperatures, Ti alloys (or C-fiber composites) have the highest specific strength, but at higher temperatures Ni alloys are superior.

  17. Ni SUPERALLOYS Thus, most turbine engines have Ti alloys in the compressor stages and Ni alloys in the combustion section.

  18. THE DISLOCATION Metals deform (bend) by motion of tiny defects called dislocations.

  19. Ni SUPERALLOY STRENGTHENING MECHANISMS The strength of pure Ni is too low for use in turbines. Ni superalloys were developed to improve strength properties, esp. strength at high temperature. • Three strengthening strategies are used in Ni superalloys: • · Solid solution hardening · Coherent precipitate hardening · Carbide phases on grain boundaries

  20. TOTAL STRENGTH IN Ni SUPERALLOYS Dislocations in g phase have difficulty shearing into the g’ phase even though the interface is coherent, thus the g’ also strengthens the alloy by blocking dislocations. Pile-up of bowed dislocations in a g channel between g’ cuboid ppts.

  21. PROGRESS IN SUPERALLOY DEVELOPMENT Alloy improvements have substantially raised the maximum operating temperatures of Ni superalloys.