casing string

the entire length of all the joints of casing run in a well. Most casing joints are manufactured to specifications established by API, although non-API specification casing is available for special situations. Casing manufactured to API specifications is available in three length ranges. A joint of range 1 casing is 16 to 25 beet long; a joint of range 2 casing is 25 to 34 feet long; and a joint of range 3 casing is 34 to 48 feet long. The outside diameter of a joint of API casing ranges from 4 1/2 o 20 inches. ...

Casing string

The steel tubing that lines a well after it has been drilled. It is formed from sections of steel tube screwed together.
Found on http://www.oilandgasuk.co.uk/glossary.cfm
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