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Note 31 - Principal Subsidiaries - Percentage of Ownership of Each Controlled Company (Details)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
HYDRIL COMPANY and subsidiaries [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership   100.00%  
CANADA | ALGOMA TUBES INC. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
CANADA | PRUDENTIAL STEEL LTD. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1],[2] 100.00% 100.00% 100.00%
CANADA | TENARIS GLOBAL SERVICES (CANADA) INC. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
BRAZIL | CONFAB INDUSTRIAL S.A. and subsidiaries [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
ITALY | DALMINE S.p.A. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
UNITED STATES | HYDRIL COMPANY and subsidiaries [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1],[3] 100.00% 100.00% 100.00%
UNITED STATES | IPSCO TUBULARS INC. and subsidiaries [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00%    
UNITED STATES | MAVERICK TUBE CORPORATION and subsidiaries [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
UNITED STATES | TENARIS BAY CITY, INC. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
UNITED STATES | TENARIS GLOBAL SERVICES (U.S.A.) CORPORATION [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
KAZAKHSTAN | Kazakhstan Pipe Threaders Limited [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
JAPAN | NKKTUBES [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 51.00% 51.00% 51.00%
INDONESIA | PT SEAMLESS PIPE INDONESIA JAYA [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 89.00% 89.00% 89.00%
ROMANIA | S.C. SILCOTUB S.A. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
SAUDI ARABIA | Saudi Steel Pipe Company [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1]   48.00%  
ARGENTINA | SIAT SOCIEDAD ANONIMA [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
ARGENTINA | SIDERCA S.A.I.C. and subsidiaries [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
PORTUGAL | TALTA—TRADING E MARKETING SOCIEDADE UNIPESSOAL LDA. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
NETHERLANDS | TENARIS CONNECTIONS BV [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
NETHERLANDS | TENARIS INVESTMENTS (NL) B.V. and subsidiaries [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00%  
URUGUAY | TENARIS FINANCIAL SERVICES S.A. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
URUGUAY | TENARIS GLOBAL SERVICES S.A. and subsidiaries [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1],[4] 100.00% 100.00% 100.00%
UNITED KINGDOM | TENARIS GLOBAL SERVICES (UK) LTD [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
LUXEMBOURG | TENARIS INVESTMENTS S.àr.l. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
Colombia | TENARIS TUBOCARIBE LTDA. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
MEXICO | TUBOS DE ACERO DE MEXICO S.A. [member]      
Disclosure of subsidiaries [line items]      
Percentage of ownership [1] 100.00% 100.00% 100.00%
[1] All percentages rounded.
[2] See note 36.
[3] Tenaris Investments S.a.r.l. holds 100 % of Hydril's subsidiaries shares except for Technical Drilling & Production Services Nigeria. Ltd where it held 80% for 2019 and 2018.
[4] Tenaris holds 97.5% of Tenaris Supply Chain S.A. and 40% of Tubular Technical Services Ltd. and Pipe Coaters Nigeria Ltd., 49% of Amaja Tubular Services Limited, 49% of Tubular Services Angola Lda and 60% of Tenaris Baogang Baotou Steel Pipes Ltd.