term we used is car-seal open (cso) . normally it is installed on block valve that you wanted to stay open (cso) such as the isolation for relief valves to ensure its operability. Christhopher Wright has posted a thread on this subject in pipingdesign.com as how the name orginated. available at emed co. inc (buffalo, NY).
Car seal comes from the rail car and freight industry. Once rail cars were filled, an inspector placed a metal wire on the loading valves. If the wire seal was broken, then the shipment could be refused. Each seal had a serial number or an imprint of the inspectors company. In the chemical industry it is an administrative control system to assure valves are not used inappropriately. For example, valves under relief valves are sealed open. This is better than chains and locks that used to be used in plants. If the valve is accessable by the public, like pipelines, then chains and locks are still used.
Car-seal open / closed is typical a sytem put in place to re duce human error. inadvertantly closing an valvethatneeds to remain open like a bolck valve under a relief valve for serviceing the releif valve while operating.
Usually there are procedures specifc to the process for the removal of the car-seal and/or not limited to written autoriztions, reductions in process operting condtions, isolation of areas etc. etc.
