Federal agency urges Minnesota to re-examine bridges for deadly design flaw.
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Transcript of Federal agency urges Minnesota to re-examine bridges for deadly design flaw.
Federal agency urges Minnesota to re-examine bridges for deadly design flaw.In continuing coverage from yesterday's briefing, NBC Nightly News (1/15, story 5, Williams) reported that the National Transportation Safety Board (NTSB) "today said a design mistake involving 16 separate plates from the center span was what they called 'the critical factor' in" the deadly Minneapolis, Minnesota bridge collapse last year. CBS Evening News (1/15, story 7, Couric) pointed out that federal investigators described steel connectors as "simply too thin." The New York Times (1/16, A17, Wald, Davey) adds, "The Federal Highway Administration moved quickly Tuesday to tell state authorities to re-examine bridges to make sure they do not have the newly discovered design flaw that doomed the Interstate 35W bridge." Revealing "its findings in the bridge collapse," the NTSB also "recommended an analysis of the flawed parts, known as gusset plates, every time major work was done on a bridge. There are about 12,600 bridges nationwide that could be vulnerable to the kind of design error found in Minneapolis." The AP (1/16, Frommer) explains that, although the NTSB is saying that "a design error led to the collapse" of the Minneapolis bridge and that "undersized gusset plates are used in the interstate bridge," the safety board "is stopping short of saying the gusset plates caused the collapse." NTSB chairman Mark Rosenker said that "the plates, which connected steel beams, were roughly half the thickness they should have been" and that "investigators found 16 fractured gusset plates from the bridge's center span." However, Rosenker "says the agency's investigation found no evidence that cracking, corrosion or other wear 'played any role in the collapse of the bridge.'" Investigators "also found no flaws in the steel and concrete material used in the bridge."
Evaluation of Corrosion
Chapter 1
1H
Valence Electrons of the ElementsHe
1 2
2Li Be
Common Metals of Commercial Importance
B C N O F Ne
2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8
3Na Mg Al Si P S Cl Ar
2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8
4K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
2,8,8,1 2,8,8,2 2,8,9,2 2,8,10,2 2,8,11,2 2,8,13,1 2,8,13,2 2,8,14,2 2,8,15,2 2,8,16,2 2,8,18,1 2,8,18,2 2,8,18,3 2,8,18,4 2,8,18,5 2,8,18,6 2,8,18,7 2,8,18,8
5Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
2,8,188,1
2,8,188,2
2,8,189,2
2,8,1810,2
2,8,1812,1
2,8,1813,1
2,8,1814,1
2,8,1815,1
2,8,1816,1
2,8,1818,0
2,8,1818,1
2,8,1818,2
2,8,1818,3
2,8,1818,4
2,8,1818,5
2,8,1818,6
2,8,1818,7
2,8,1818,8
6
Cs Ba * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
2,8,1818,8,1
2,8,1818,8,2
2,8,1832,10,2
2,8,1832,11,2
2,8,1832,12,2
2,8,1832,13,2
2,8,1832,14,2
2,8,1832,15,2
2,8,1832,17,1
2,8,1832,18,1
2,8,1832,18,2
2,8,1832,18,3
2,8,1832,18,4
2,8,1832,18,5
2,8,1832,18,6
2,8,1832,18,7
2,8,1832,18,8
Corrosion of Zinc Plated Screws in Sulfuric Acid
Definitions
Anode• Point where oxidation
occurs• Atoms lose electrons
and become oxidized• Oxidized atoms can
become soluble in the electrolyte
Cathode• Point where reduction
occurs• Atoms gain electrons
and become reduced• Reduced atoms may
“plate” out on the cathode
Reactions at Anode
• Metal is oxdizedM Mn+ + ne-
• Fe Fe2+ + 2e-
• Al Al3+ + 3e-
• Cu Cu2+ + 2e-
Reactions at Cathode
• Deaerated Water (No Oxygen)2H+ + 2e- H2
• Aerated Water (Oxygen Present)O2 + 4H+ + 4e- 2H2O (Acidic)O2 + 2H2O + 4e- 4OH- (Neutral/Basic)
• Dissolved IronFe3+ + e- Fe2+
Corrosion Rate Measurement
hours time, ExposureTinches squareexposure, of AreaA
g/cm density, MetalDmg loss, WeightW
inches0.0011milyear per milsMPY
DAT
WMPY
3
534
Corrosion Rate ExperimentDay Insert Remove Sample Exposure
1 (Wednesday) Samples 1, 2, 3
3 (Friday) Sample 1 2 Days
6 (Monday) Sample 4 Sample 2 5 Days
8 (Wednesday) Samples 3, 4 7, 2 Days
•If Samples 1 and 4 have the same mass loss, then the corrosiveness of of the solution is unchanged•If Sample 4 has a lower mass loss, then the corrosiveness decreased•If Sample 4 has a higher mass loss, then the corrosiveness increased
•If Samples 3 and has the same mass loss as Samples 1 and 2 combined, then the corrodibility does not change•If Sample 3 has a lower mass loss, then the corrodibility decreased•If Sample 3 has a higher mass loss, then the corrodibility increased
In-Class ProblemCorrosion of Carbon Steel
• 2” x 3” x 0.123” with 0.25” hole• Sample 1: 12 hours, 25 mg loss• Sample 2: 108 hours, 130 mg loss• Sample 3: 120 hours, 150 mg loss• Sample 4: 12 hours, 15 mg loss (inserted when
Sample 2 was removed)Calculate the corrosion rates for each sample and
determine if there are changes in corrodibility or corrosiveness. D = 7.9 g/cm3
Homework #1 Due 1/25 (Friday)
• Read Chapter 1 of textbook• Answer Problems 1-5 and 1-7 at end of
chapter• Use the internet to find how corrosion
contributed to an accident. Prepare a brief (1 page) summary of the type of corrosion (crevice, stress corrosion cracking, etc) and how it precipitated the accident.