Shipping companies have snapped up dozens of secondhand oil tankers this year, paying record prices for ice-class ships that can navigate frozen seas around Russia’s Baltic ports in winter. A driving force behind the purchases, say people familiar with the deals: To get Russian oil to market after the harshest sanctions to date strike Russia’s energy industry next week. The frenzy in a quiet corner of the shipping market is splitting the tanker industry in two. One part deals with Western oil companies, banks and insurers. The other, known informally in the industry as the “shadow fleet,” doesn’t, allowing it...