'Comedy of errors' led to bad bridge bolts Series of mistakes by manufacturer and Caltrans left Bay Bridge rods susceptible to rainwater, expert says

Pier E-2 (right) contains the broken giant anchor rods that in a flawed process became brittle and vulnerable to failure. Pier E-2 (right) contains the broken giant anchor rods that in a flawed process became brittle and vulnerable to failure. Photo: Michael Macor, The Chronicle Photo: Michael Macor, The Chronicle Image 1 of / 1 Caption Close 'Comedy of errors' led to bad bridge bolts 1 / 1 Back to Gallery

The failure of seismic-safety bolts on the new eastern span of the Bay Bridge was the product of a series of apparent errors and miscalculations that left once-robust steel prey to simple rainwater, several experts told The Chronicle.

"The bottom line is they used the wrong bolts for this application," said Louis Raymond, a corrosion expert in Newport Beach (Orange County) who has been involved in setting bolt safety standards and resilience testing for more than 30 years. "Those bolts had very low damage tolerance."

Thirty-two bolts that anchor seismic-safety structures to the $6.4 billion bridge broke last month after workers tightened them. Transportation officials say there is no guarantee that Caltrans can engineer a solution in time for the span's scheduled opening to traffic Sept. 3.

Tony Anziano, Caltrans' toll bridge project manager, referred to a "paperwork" problem with the bolts in a briefing to the Metropolitan Transportation Commission on Wednesday. In a subsequent interview, however, he outlined a string of events that experts say made the bolts vulnerable, beginning in 2008 when the first 96 rods were forged and then tempered.

The tempering process subjects the 17-foot-long bolts to 800-degree heat to make them both pliable and strong. However, the contractor responsible for the process - whom the state has not identified - failed to produce documents showing that all the bolts had been properly heat-treated, so Caltrans ordered that they be baked again, Anziano said.

The twice-baked bolts were now much harder than required by industry standards, Caltrans acknowledges. Experts believe it was that extra hardness that was the key to their ultimate demise.

Hard steel vulnerable

Corrosion engineers have long understood that the harder the steel, the less it can resist becoming brittle and cracking when it is exposed to hydrogen. Hard steel, they say, is vulnerable to snapping when hydrogen invades and forms bubbles at high stress points.

"When you are forced to use materials of that strength, you would really want to be careful," said John Scully, a University of Virginia corrosion and hydrogen embrittlement expert. "When you work in the field of hydrogen embrittlement, the hardness (of the bridge bolts) would have gone off like a firecracker in your head."

After being heat-treated twice, the bolts were dipped in molten zinc, a process called galvanization that is supposed to keep them free of rust and corrosion caused by the marine air.

Damaging reaction

Galvanization is supposed to short-circuit an electro-chemical reaction that happens when steel is exposed to a corrosive marine environment. The zinc acts as a barrier in this reaction, supposedly leaving hydrogen to rest harmless on the surface.

But experts said any break or scrape in the galvanized coating would allow hydrogen created in that electro-chemical reaction to invade the steel.

Raymond said the reaction "literally pumps hydrogen into the steel. When it is put under high stress, it acts like a sponge for sucking in hydrogen."

Once they were delivered to the bridge in 2008, the zinc-coated bolts were installed in holes on a concrete cap atop a pillar. Those holes later filled with rainwater, which experts say likely found its way into the extra-vulnerable steel via tiny flaws in the zinc coating.

Having a high-strength, galvanized bolt sit in rainwater "is a definite recipe for a hydrogen embrittlement," Raymond said.

"They were made harder, they had the galvanizing and then sat around in water - it's kind of a comedy of errors and when they all multiply, they become severe," said Russell Kane of Houston, an oil industry consultant on corrosion and hydrogen-caused cracking of steel structures.

"The material can handle one error, or maybe two," Kane said. "But eventually it can't handle it any more and you get unexpected failure."

Caltrans tests taken when the bolts were delivered to the eastern span showed that the twice-heated steel was very hard - with some of the rods having a tensile strength of 170,000 pounds per square inch, Anziano said. That level is well beyond the minimum acceptable level of 140,000 pounds for that grade of bolt, experts say, and put the bolts at greater risk of cracking if exposed to hydrogen.

Unexpected problem

Raymond noted that that industry specifications normally bar such high-strength structural steel from being galvanized, to guard against the risk that hydrogen could invade and be locked into the metal during that process or from entering through microscopic gaps in the zinc after the steel is put in place.

Caltrans, however, accepted the galvanized bolts because the agency believed that hydrogen had been eliminated from the galvanizing process, Anziano said. It did not foresee the problem with the bolts being left in rainwater, he said.

He said Caltrans still does not know exactly when the hydrogen got into the steel bolts - during the manufacturing, or in the five years that the bolts sat in place on the bridge before being tightened, in the rainwater-filled holes. Four bolts have so far been removed for examination.

Repairs could take months

Caltrans officials told members of the Metropolitan Transportation Commission on Wednesday that the more than 2,000 other galvanized, high-strength steel bolts on the bridge have not been exposed to as much rainwater and are not tightened to such a level that they could be at risk of cracking.

One state official said Wednesday that it could take months to come up with a fix for the broken bolts. But the Metropolitan Transportation Commission's deputy operations director, Andrew Fremier, also floated the possibility of opening the new span on time if engineers decide that even without a permanent repair, the bridge is still safer than the existing, earthquake-vulnerable eastern span.