The Plan 66A is an API piping plan for leakage containment primarily intended for use on crude oil (pipeline) duties. Crude liquid hydrocarbon pipelines represent 1/3rd of total liquid hydrocarbon mileage. The arrangement is generally used on single seal installations ? marginalizing this as a North American solution where single seals on crude pipeline applications are still common. Whilst it is intended for wide spread use there are only a few primary operators that have adopted this type of containment technology. Many operators still deploy plan 65 arrangements, whilst others have moved from Plan 65?s or similar to a full API Type 2 arrangements employing a full back up mechanical seal.