UNITED STATES
                        SECURITIES AND EXHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13D
                    Under the Securities Exchange Act of 1934
                               (Amendment No. 38)*

                         TUBOS DE ACERO DE MEXICO, S.A.
--------------------------------------------------------------------------------
                                (Name of Issuer)

                                  Common Stock
--------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                    898592506
--------------------------------------------------------------------------------
                                 (CUSIP Number)

                            Mr. Fernando R. Mantilla
           Av. Leandro N. Alem 1067, 28th Floor, 1001 - Buenos Aires,
                          Argentina (54-11) 4018-2245
--------------------------------------------------------------------------------
           (Name, Address and Telephone Number of Person Authorized to
                       Receive Notices and Communications)

                                  July 3, 2003
--------------------------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)

         If the filing person has  previously  filed a statement on Schedule 13G
         to report the acquisition that is the subject of this Schedule 13D, and
         is filing this schedule because of ss.ss.240.13d-1(e),  240.13d-1(f) or
         240.13d-1(g), check the following box. |_|

         Note:  Schedules  filed in paper format shall include a signed original
         and  five  copies  of  the  schedule,   including  all  exhibits.   See
         ss.240.13d-7 for other parties to whom copies are to be sent.

         *The  remainder  of this cover page shall be filled out for a reporting
         person's  initial filing on this form with respect to the subject class
         of securities,  and for any subsequent amendment containing information
         which would alter disclosures provided in a prior cover page.

         The information  required on the remainder of this cover page shall not
         bee  deemed  to be  "filed"  for  the  purpose  of  Section  18 of  the
         Securities  Exchange Act of 1934  ("Act") or  otherwise  subject to the
         liabilities  of that  section  of the Act but shall be  subject  to all
         other provisions of the Act (however, see the Notes).



CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                 SIDERCA Sociedad Anonima Industrial y Comercial
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             ARGENTINA
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check if the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------



CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                            SIDERCA INTERNATIONAL ApS
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             DENMARK
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check if the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------



CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                        ROCCA & PARTNERS Sociedad Anonima
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             BRITISH VIRGIN ISLANDS
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check if the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------



CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                                SAN FAUSTIN N.V.
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             NETHERLANDS ANTILLES
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check If the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------




CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                                 SIDERTUBES S.A.
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             LUXEMBOURG
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check if the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------




CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                       I.I.I. INDUSTRIAL INVESTMENTS INC.
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             BRITISH VIRGIN ISLANDS
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check if the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------




CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                                  TENARIS S.A.
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             LUXEMBOURG
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check if the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------




CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                                  INVERTUB S.A.
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             ARGENTINA
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check if the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------




CUSIP No. 898592506
--------------------------------------------------------------------------------
     1   Name of Reporting Persons

         I.R.S. Identification Nos. of above persons (entities only):

                                 SIDTAM LIMITED
--------------------------------------------------------------------------------
     2   Check the Appropriate Box If a Member of a Group (See Instructions)
           (a)  [_]
           (b)  [ ]
--------------------------------------------------------------------------------
     3   SEC Use Only

--------------------------------------------------------------------------------
     4   SOURCE OF FUNDS: (See Instructions)   NOT APPLICABLE
--------------------------------------------------------------------------------
     5   Check if Disclosure of Legal Proceedings
         is Required Pursuant to Item 2(d) OR 2(e)        [_]
--------------------------------------------------------------------------------
     6   Citizenship or Place of Organization             BRITISH VIRGIN ISLANDS
--------------------------------------------------------------------------------
                       7    Sole Voting Power             NONE
  Number of           ----------------------------------------------------------
  Shares               8    Shared Voting Power           320,414,223 Shares of
  Beneficially                                            TAMSA Common Stock (1
  Owned by Each                                           ADR=5 shares)
  Reporting           ----------------------------------------------------------
  Person With          9    Sole Dispositive Power        NONE
                      ----------------------------------------------------------
                      10    Shared Dispositive Power      320,414,223 Shares of
                                                          TAMSA Common Stock (1
                                                          ADR=5 shares)
--------------------------------------------------------------------------------
     11  Aggregate Amount Beneficially Owned by
         Each Reporting Person:                           320,414,223
--------------------------------------------------------------------------------
     12  Check if the Aggregate Amount in Row (11)
         Excludes Certain Shares (See Instructions)       NOT APPLICABLE
--------------------------------------------------------------------------------
     13  Percent of Class Represented
         by Amount in Row (11):                           94.44%
--------------------------------------------------------------------------------
     14  Type of Reporting Person: (See Instructions)     CO
--------------------------------------------------------------------------------




                        AMENDMENT No. 38 TO SCHEDULE 13D

This Amendment No. 38 amends the Statement on Schedule 13D  originally  filed on
September  24, 1992 and amended and restated as of November 11, 2002, as amended
("Schedule 13D"), on behalf of Siderca Sociedad Anonima,  Industrial y Comercial
("Siderca SAIC"), and Siderca  International ApS ("Siderca ApS"),  together with
Rocca & Partners S.A.  ("Rocca & Partners"),  San Faustin N.V. ("San  Faustin"),
Sidertubes S.A. ("Sidertubes"),  I.I.I. Industrial Investments Inc. ("III BVI"),
Tenaris S.A.  ("Tenaris"),  Invertub  Sociedad  Anonima  ("Invertub") and Sidtam
Limited ("Sidtam") (collectively,  "Reporting Persons"),  relating to the common
shares,  without  par value (the "TAMSA  Shares"),  of Tubos de Acero de Mexico,
S.A., a Mexican company ("TAMSA").

      Item 2. Identity and Background

No changes.

      Item 4. Purpose of the Transaction

As reported in Amendment No. 36 to the Schedule 13D, Tenaris  announced on March
31, 2003 that,  subject to the  approvals  of the U.S.  and  Mexican  securities
regulators and TAMSA's extraordinary  shareholders  meeting,  Tenaris intends to
effect an exchange of its shares and ADSs for any TAMSA shares and ADSs not held
by Tenaris or its affiliates in accordance with Mexican and U.S. laws.

Reference is now made to the registration statement of Form F-4 filed by Tenaris
on July 3, 2003 with the U.S.  Securities and Exchange  Commission  (the "SEC"),
relating to Tenaris's  offer to exchange its ADSs for any TAMSA ADSs not held by
Tenaris or its affiliates.

Under the terms of the proposed exchange offer,  Tenaris would offer to exchange
one Tenaris ADS  (representing  10 ordinary  shares of Tenaris) for every 9.4520
common shares of TAMSA tendered, and one Tenaris ADS for every 1.8904 Tamsa ADSs
tendered.

The registration  statement has not yet been declared  effective by the SEC, and
Tenaris  will not launch the  exchange  offer until it has obtained all relevant
approvals  from the SEC and all other relevant U.S. or Mexican  authorities.  No
assurances  can be given that Tenaris will be able to meet all the  requirements
for the  approvals  or that the  relevant  authorities  will grant the  required
approvals.  In addition, the completion of the exchange offer, if and when it is
launched,  is subject to certain  conditions,  as discussed in the  registration
statement,  and  Tenaris  reserves  the  right to  modify  or waive any of these
conditions in its discretion, subject to applicable law.

      Item 5. Interest in Securities of the Issuer

As disclosed in TAMSA's  annual report on Form 20-F for the year ended  December
31, 2002, filed with the SEC on June 30, 2003, TAMSA cancelled  3,650,000 shares
of TAMSA held by its  subsidiary  Tamsider on April 30, 2003,  and, as a result,
Tenaris's  ownership of TAMSA's  outstanding capital stock was reduced to 94.44%
from 94.50%.



      Item 7. Material to be Filed as Exhibits

Powers of attorney for Tenaris  S.A.,  I.I.I.  Industrial  Investments  Inc. and
Invertub  S.A. are  incorporated  by reference  into this  Amendment to the ones
filed as exhibits to Amendment  No. 34 to the Schedule  13D.  Powers of attorney
for each of the other Reporting  Persons are incorporated by reference into this
Amendment to the ones filed as exhibits to Amendment  No. 23 to the Schedule 13D
of Siderca ApS.

The written  agreement of the  Reporting  Persons  related to the filing of this
Schedule  13D as required  by Rule  13d-k(1)(iii)  is included in the  signature
pages hereto and is hereby filed as an exhibit hereto.



                                    SIGNATURE

      After  reasonable  inquiry and to the best of my knowledge and belief,  I,
Fernando  Mantilla,  attorney  duly  authorized by ROCCA & PARTNERS S.A. to sign
this  statement,  certify that the information set forth in this Schedule 13D is
true, complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule  13D on his own  behalf  and on behalf  of SAN  FAUSTIN  N.V.,  SIDERCA
Sociedad Anonima Industrial y Comercial,  SIDERCA  INTERNATIONAL ApS, SIDERTUBES
S.A.,  I.I.I.  INDUSTRIAL  INVESTMENTS  Inc.,  TENARIS S.A.,  INVERTUB  Sociedad
Anonima and SIDTAM LIMITED.

July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact



                                    SIGNATURE

      After  reasonable  inquiry and to the best of my knowledge and belief,  I,
Fernando  Mantilla,  attorney  duly  authorized by SAN FAUSTIN N.V. to sign this
statement,  certify that the information set forth in this Schedule 13D is true,
complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule 13D on his own behalf and on behalf of ROCCA & PARTNERS  S.A.,  SIDERCA
Sociedad Anonima Industrial y Comercial,  SIDERCA  INTERNATIONAL ApS, SIDERTUBES
S.A.,  I.I.I.  INDUSTRIAL  INVESTMENTS  Inc.,  TENARIS S.A.,  INVERTUB  Sociedad
Anonima and SIDTAM LIMITED.

July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact



                                    SIGNATURE

      After  reasonable  inquiry and to the best of my knowledge and belief,  I,
Fernando  Mantilla,  attorney duly authorized by I.I.I.  INDUSTRIAL  INVESTMENTS
Inc. to sign this  statement,  certify  that the  information  set forth in this
Schedule 13D is true, complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule  13D on his own  behalf  and on behalf of ROCCA &  PARTNERS  S.A.,  SAN
FAUSTIN  N.V.,  SIDERCA  Sociedad  Anonima   Industrial  y  Comercial,   SIDERCA
INTERNATIONAL ApS,  SIDERTUBES S.A., TENARIS S.A., INVERTUB Sociedad Anonima and
SIDTAM LIMITED.

July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact



                                    SIGNATURE

      After  reasonable  inquiry and to the best of my knowledge and belief,  I,
Fernando  Mantilla,  attorney duly  authorized  by SIDERTUBES  S.A. to sign this
statement,  certify that the information set forth in this Schedule 13D is true,
complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule  13D on his own  behalf  and on behalf of ROCCA &  PARTNERS  S.A.,  SAN
FAUSTIN  N.V.,  SIDERCA  Sociedad  Anonima   Industrial  y  Comercial,   SIDERCA
INTERNATIONAL  ApS,  I.I.I.   INDUSTRIAL  INVESTMENTS  Inc.,  INVERTUB  Sociedad
Anonima, TENARIS S.A. and SIDTAM LIMITED.

July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact



                                    SIGNATURE

      After reasonable inquiry and to the best of my knowledge and belief, I,
Fernando  Mantilla,  attorney  duly  authorized  by  TENARIS  S.A.  to sign this
statement,  certify that the information set forth in this Schedule 13D is true,
complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule  13D on his own  behalf  and on behalf of ROCCA &  PARTNERS  S.A.,  SAN
FAUSTIN  N.V.,  SIDERCA  Sociedad  Anonima   Industrial  y  Comercial,   SIDERCA
INTERNATIONAL ApS, SIDERTUBES S.A., I.I.I. INDUSTRIAL INVESTMENTS Inc., INVERTUB
Sociedad Anonima and SIDTAM LIMITED.

July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact



                                    SIGNATURE

      After  reasonable  inquiry and to the best of my knowledge and belief,  I,
Fernando  Mantilla,  attorney  duly  authorized  by  INVERTUB  S.A. to sign this
statement,  certify that the information set forth in this Schedule 13D is true,
complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule  13D on his own  behalf  and on behalf of ROCCA &  PARTNERS  S.A.,  SAN
FAUSTIN  N.V.,  SIDERCA  Sociedad  Anonima   Industrial  y  Comercial,   SIDERCA
INTERNATIONAL ApS, SIDERTUBES S.A., I.I.I.  INDUSTRIAL INVESTMENTS Inc., TENARIS
S.A. and SIDTAM LIMITED.


July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact



                                    SIGNATURE

      After  reasonable  inquiry and to the best of my knowledge and belief,  I,
Fernando  Mantilla,   attorney  duly  authorized  by  SIDERCA  SOCIEDAD  ANONIMA
INDUSTRIAL Y COMERCIAL to sign this statement,  certify that the information set
forth in this Schedule 13D is true, complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule  13D on his own  behalf  and on behalf of ROCCA &  PARTNERS  S.A.,  SAN
FAUSTIN N.V.,  SIDERCA  INTERNATIONAL  ApS,  SIDERTUBES S.A., I.I.I.  INDUSTRIAL
INVESTMENTS Inc., TENARIS S.A., INVERTUB S.A. and SIDTAM LIMITED.


July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact



                                    SIGNATURE

      After  reasonable  inquiry and to the best of my knowledge and belief,  I,
Fernando Mantilla, attorney duly authorized by SIDERCA INTERNATIONAL ApS to sign
this  statement,  certify that the information set forth in this Schedule 13D is
true, complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule  13D on his own  behalf  and on behalf of ROCCA &  PARTNERS  S.A.,  SAN
FAUSTIN N.V., SIDERCA Sociedad Anonima Industrial y Comercial,  SIDERTUBES S.A.,
I.I.I.  INDUSTRIAL INVESTMENTS Inc., TENARIS S.A., INVERTUB Sociedad Anonima and
SIDTAM LIMITED.


July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact



                                    SIGNATURE

      After  reasonable  inquiry and to the best of my knowledge and belief,  I,
Fernando  Mantilla,  attorney  duly  authorized  by SIDTAM  LIMITED to sign this
statement,  certify that the information set forth in this Schedule 13D is true,
complete and correct.

      Pursuant to Rule 13d-1(k)(1),  the undersigned joins in the filing of this
Schedule  13D on his own  behalf  and on behalf of ROCCA &  PARTNERS  S.A.,  SAN
FAUSTIN  N.V.,  SIDERCA  Sociedad  Anonima   Industrial  y  Comercial,   SIDERCA
INTERNATIONAL  ApS, I.I.I.  INDUSTRIAL  INVESTMENTS Inc.,  TENARIS S.A. INVERTUB
Sociedad Anonima and SIDERTUBES S.A.

July 8, 2003

                                                     /s/ Fernando Mantilla
                                                     ---------------------
                                                         Fernando Mantilla
                                                          Attorney-in-fact




Exhibit index:

99.1  Powers of attorney (incorporated by reference to Amendments No. 23 and 34)

99.2  Written agreement of the Reporting Persons (included in signature pages)