CPC Subgroup
E21B 17/012 Full Title
Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Casings; Tubings > Risers
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E21B 17/012 Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Casings; Tubings > Risers