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This is the final highway accident report (NTSB-HAR-71-1) from the National Transportation Safety Board, adopted in December 1970. It covers the collapse of the U.S. 35 bridge between Point Pleasant, West Virginia, and Kanauga, Ohio, on December 15, 1967, which killed 46 people. The Board found that the cause was a cleavage fracture in eyebar 330 at joint C13N. That fracture grew from a flaw produced over 40 years by stress corrosion and corrosion fatigue, in a spot that could not be seen or found by inspection.
“Harder”1 page
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Condition B: 0.004% by weight of sulfuric acid in distilled water, plus a poison. Condition E-1: Hydrogen sulfide gas dissolved in water by continuous bubbling. Condition E-2: Same as E-1, except that the specimen was coupled with a commercially pure aluminum anode. The charging currents established by these exposures were measured. Sustained loads applied to the specimens produced stress intensity factors between 26.4 and 45.0 ksi. in. Hydrogen entry rates under the same set of environments were independently measured by samples exposed in a vacuum-permeation cell. The study showed that the steel without pre-existing defects was susceptible to hydrogen-stress-cracking only under severe cathodic charging conditions and high stress levels. The investigators also made the following observations: (1) The steel from the inside surface of the pinhole was more susceptible than that from the outer surface of the eyebar because of the removal of the decarburized layer in the machining of the hole, exposing the harder material. Some of this material was extremely hard (51 Rockwell C by conversion), due apparently to localized cold working. (2) There was considerable metallurgical variation between specimens, which may account for some of the apparent inconsistency of results. (3) There was an indication that the hardest layers of steel were susceptible to stress-corrosion cracking (not requiring the presence of atomic hydrogen) in a hydrogen sulfide environment. Further investigations of the stress-corrosion cracking susceptibility are reported in Section VI of the Battelle report. In these investigations, the emphasis was on the determination of the threshold value of the stress intensity factor below which no stress-corrosion crack propagation could occur in each of two environments; namely, 100 percent relative humidity air, and a solution of 0.5 percent hydrogen sulfide and 5 percent salt in distilled water. Two types of specimens were used. Six ordinary surface flawed specimens were exposed to each environment at various static stress levels to obtain values for plotting curves from which the threshold value could be determined. "Wedge loaded" specimens were also tested in each environment. This form of specimen has the advantage that, as cracking proceeds, the
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