Supplier of Bay Bridge bolts criticized in earlier Caltrans audit
04/12/2013 5:29 PM
04/12/2014 7:26 PM
A year before Ohio-based Dyson Corp. supplied the giant bolts that recently ruptured on the new Bay Bridge, a California Department of Transportation auditor flagged the firm for deficiencies in related areas.
On Friday, Caltrans released the audit and test documents that detail some likely causes for the problem with the bolts, designed to secure essential seismic safety equipment on the bridge.
Caltrans' critical 2007 audit of Dyson showed that the company "had no capability for testing galvanizing thickness." Steel is galvanized to help prevent corrosion.
The audit also cited numerous problems in the firm's heat treatment area, including a failure to consistently maintain "temperature record graphs."
Heat-treatment records were part of the problem with the faulty bolts.
The audit criticized Dyson's procedures and gave the company a "contingent pass," recommending improvements to achieve a passing grade. The bolts that broke on the bridge were installed in 2008.
Caltrans has blamed the problem on hydrogen contamination that made the steel brittle.
The agency said earlier this week that the bolts had failed elongation tests but were still judged suitable for use.
Non-conformance reports and other information released Friday suggested that several interrelated problems probably played a role in the bolts breaking.
The bolts failed last month when they were stressed, or placed under tension, to increase overall performance. A remedy for the problem, its cost and whether the opening of the bridge must be delayed have not been determined yet.
The agency plans to build a work-around to replace the function of 96 anchor bolts, also called rods, installed in 2008 on two of the four seismic shear keys.
Of those bolts, 32 snapped.
Another 192 bolts, installed in 2010 to secure two other shear keys and four giant seismic bearings, so far have shown no signs of breakage after having been tightened.
Missing Dyson paperwork had created doubts about whether the supplier had properly heated the steel of the bolts – a process important for hardening and other quality factors.
Bay Bridge spokesman Andrew Gordon said the bolts were heated again, which apparently hardened the steel beyond normal specifications.
"The higher the strength of the steel, the more susceptible it becomes to embrittlement," Joe Payer, chief scientist of the national corrosion center at the University of Akron, said in an interview. In very hard steel, a relatively small amount of hydrogen can lead to failure, he said.
No representative for Dyson could be reached for comment.
Caltrans said hydrogen could have entered the bolts during the manufacturing process, or when the bolts were dipped in molten zinc to galvanize them.
Zinc provides a barrier between the steel bolts and water, Payer said. Rainwater contacted the bolts during the period between installation and the tightening, and corrosion apparently took place.
If the zinc layer was scraped off or corroded, Payer said, eventually water can reach the steel. This creates rust, which generates hydrogen that can then enter the steel and make it brittle.
The problem is most likely to occur in threaded regions of a bolt, Payer said.
The breaks occurred at the bottom threaded portions anchored to the bridge pier, according to Caltrans.
The Caltrans audit of Dyson was highly critical of how the company kept track of its material.
"(T)he short-term 'filing system' for recent heating graphs, some as old as two weeks, was under the desk blotter on the shift supervisor's desk," wrote Caltrans auditor Venkatesh S. Iyer.
Auditors observed "a bin of nuts with no traceability paperwork," and the nuts could not be identified by Dyson employees.
Iyer noted audit results for the two Dyson galvanizing subcontractors: One failed and the other received a contingent pass.
In one case, he cited " 'seat of the pants' judgment by galvanizing operators," who "dumped (galvanized parts) into the bins without any particular care being taken to prevent damage to the zinc coating."
On at least 14 occasions, other Dyson-supplied parts failed quality tests. Caltrans has not responded to questions about whether any of those suspect parts also were installed in the Bay Bridge.
Transportation officials hope the $6.4 billion bridge will open on Sept. 3, as planned, but conceded that the schedule might slip if an engineering work-around cannot be selected, approved and built in time.
Call The Bee's Charles Piller, (916) 321-1113. Follow him on Twitter @cpiller.
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