“You’re only as strong as your weakest link (or bolt?)”

A situation occurred earlier this year with flawed bolts halting drilling from the Gulf of Mexico to Brazil. Used in Blow-out Preventers (or BOP’s) – made infamous by the Deepwater Horizon rig back in 2010 – some bolts have failed through suspected stress corrosion cracking caused by hydrogen embrittlement. This renders each of the $45million BOP’s a safety concern until the bolts are replaced. Operational and rental costs in excess of $1m per day per rig will have to be swallowed during the time it takes to replace the bolts (read more). 

Zinc plating without proper baking (process should be – ASTM B633) has been proposed as the possible cause of the hydrogen embrittlement – please see this safety alert. 

Due to the production of Hydrogen during the plating process, a subsequent step of baking is carried out to flush out any trapped hydrogen to avoid field issues with embrittlement. The process involves; plating the components, and within a set period of time, transfer to a baking oven and hold parts at temperature (typically around 374degF) for a number of hours.

It is important at all stages during the process (plating, baking etc.) that records are kept of the processing times and temperature cycles used, this is done to ensure full traceability exists for all parts treated. These records should be examined by a QA (or similar function) department to ensure the parts have been treated to the correct cycles.

The Heat Treat and Plating industries have developed their record keeping over time, moving relatively quickly from clipboard records to paper charts and more recently Digital Recorders with tamperproof data (Paperless charts or SCADA systems). Digital systems allow quick and accurate retrieval of information across multiple process steps and pricing for this type of system is now at parity or even lower than buying new paper chart based systems.