Principal subsidiaries

The following is a list of Tenaris’s principal subsidiaries and its direct and indirect percentage of ownership of each controlled company at

December 31, 2017.

Company	Country of Incorporation	Main activity	Percentage of ownership at December 31, (*)
			2017	2016	2015
ALGOMA TUBES INC.	Canada	Manufacturing of seamless steel pipes	100%	100%	100%
CONFAB INDUSTRIAL S.A. and subsidiaries	Brazil	Manufacturing of welded steel pipes and capital goods	100%	100%	100%
DALMINE S.p.A.	Italy	Manufacturing of seamless steel pipes	100%	100%	99%
HYDRIL COMPANY and subsidiaries (except detailed) (a)	USA	Manufacture and marketing of premium connections	100%	100%	100%
MAVERICK TUBE CORPORATION and subsidiaries	USA	Manufacturing of welded steel pipes	100%	100%	100%
NKKTUBES	Japan	Manufacturing of seamless steel pipes	51%	51%	51%
P.T. SEAMLESS PIPE INDONESIA JAYA	Indonesia	Manufacturing of seamless steel products	89%	77%	77%
PRUDENTIAL STEEL LTD.	Canada	Manufacturing of welded steel pipes	100%	100%	100%
S.C. SILCOTUB S.A.	Romania	Manufacturing of seamless steel pipes	100%	100%	100%
SIAT SOCIEDAD ANONIMA	Argentina	Manufacturing of welded and seamless steel pipes	100%	100%	100%
SIDERCA SOCIEDAD ANONIMA INDUSTRIAL Y COMERCIAL and subsidiaries	Argentina	Manufacturing of seamless steel pipes	100%	100%	100%
TALTA - TRADING E MARKETING SOCIEDADE UNIPESSOAL LDA.	Portugal	Holding Company	100%	100%	100%
TENARIS BAY CITY, INC.	USA	Manufacturing of seamless steel pipes	100%	100%	100%
TENARIS FINANCIAL SERVICES S.A.	Uruguay	Financial company	100%	100%	100%
TENARIS GLOBAL SERVICES (CANADA) INC.	Canada	Marketing of steel products	100%	100%	100%
TENARIS GLOBAL SERVICES (U.S.A.) CORPORATION	USA	Marketing of steel products	100%	100%	100%
TENARIS GLOBAL SERVICES (UK) LTD	United Kingdom	Holding company and marketing of steel products	100%	100%	100%
TENARIS GLOBAL SERVICES S.A. and subsidiaries (except detailed) (b)	Uruguay	Holding company and marketing of steel products	100%	100%	100%
TENARIS INVESTMENTS S.àr.l.	Luxembourg	Holding company	100%	100%	100%
TENARIS INVESTMENTS SWITZERLAND AG and subsidiaries	Switzerland	Holding company	100%	100%	100%
TENARIS CONNECTIONS BV	Netherlands	Development, management and licensing of intellectual property	100%	100%	100%
TENARIS TUBOCARIBE LTDA.	Colombia	Manufacturing of welded and seamless steel pipes	100%	100%	100%
TUBOS DE ACERO DE MEXICO, S.A.	Mexico	Manufacturing of seamless steel pipes	100%	100%	100%

(*) All percentages rounded.

(a) Tenaris Investments S.a.r.l. holds

100%

of Hydril's subsidiaries shares except for Technical Drilling & Production Services Nigeria. Ltd where it holds

for

2017,

2016

and

2015.

(b) Tenaris holds

97,5%

of Tenaris Supply Chain S.A,

60%

of Gepnaris S.A. and

40%

of Tubular Technical Services and Pipe Coaters, and

49%

of Amaja Tubular Services Limited.