(19)

(11)

EP 0 128 206 A1

(12)

(43) Date of publication: 19.12.1984 Bulletin 1984/51 (21) Application number: 84900253.0 (22) Date of filing: 12.12.1983

(51) International Patent Classification (IPC):  E21B 21/ 00( . ) E21B 21/ 10( . ) E21B 21/ 08( . ) E21B 33/ 064( . ) (86) International application number: PCT/US1983/001936 (87) International publication number: WO 1984/002374 (21.06.1984 Gazette 1984/15)

(84) Designated Contracting States: AT BE CH DE FR GB LI LU NL SE (30) Priority: 13.12.1982 US 19820449375 13.12.1982 US 19820449376 13.12.1982 US 19820449467 13.12.1982 US 19820449531 (71) Applicant: HYDRIL COMPANY Los Angeles California 90015 (US)	(72) Inventors: KEITHAHN, Julian, D. Houston, TX 77079 (US) MORRILL, Charles, D. Humble, TX 77338 (US) ROCHE, Joseph, R. Humble, TX 77338 (US) ALEXANDER, Gabriel, G. Houston, TX 77060 (US) TIPPIT, Larry, J. The Woodlands, TX 77380 (US) (74) Representative: Madgwick, Paul Roland, et al  Ladas & Parry Altheimer Eck 2 D-80331 München D-80331 München (DE)