The Coast Guard has decided (somewhat belatedly) to implement IMO Resolution MSC.105(73) by not allowing any US flag non-double hull tank ship 15 years and older that trades internationally and is subject to SOLAS to conduct an underwater inspection in lieu of drydock (UWILD). A certificated tug and non-double hull barge that operate as a push-mode ITB is treated by the Coast Guard as a tank ship for this purpose.
Source: HK Law