(19)

(11)

EP 0 139 724 A1

(12)

(43) Date of publication: 08.05.1985 Bulletin 1985/19 (21) Application number: 84901685.0 (22) Date of filing: 06.04.1984

(51) International Patent Classification (IPC):  E21B 33/ 06( . ) (86) International application number: PCT/US1984/000507 (87) International publication number: WO 1984/004130 (25.10.1984 Gazette 1984/25)

(84) Designated Contracting States: AT BE CH DE FR GB LI LU NL SE (30) Priority: 18.04.1983 US 19830485619 (71) Applicant: HYDRIL COMPANY Los Angeles California 90015 (US)	(72) Inventors: HYNES, Joseph, H. Houston, TX 77069 (US) BURTON, James, A. Houston, TX 77040 (US) (74) Representative: Baillie, Iain Cameron, et al  c/o Ladas & Parry Altheimer Eck 2 D-80331 München D-80331 München (DE)