<PAGE>
                                                                    EXHIBIT 10.6

                  AMENDMENT AND RESTATEMENT TO CREDIT AGREEMENT

         This Amendment and Restatement to Credit Agreement (this "Amendment")
dated to be effective as of May 1, 2001 (the "Amendment") is among THE SHAW
GROUP, INC., a Louisiana corporation (the "Borrower"), the Subsidiaries of the
Borrower listed on the signature pages hereto as Guarantors, the banks and other
financial institutions listed on the signature pages attached hereto (the
"Lenders"), BANK ONE, NA, whose main office is in Chicago, Illinois,
individually as a Lender ("Bank One"), as Issuer and as administrative agent for
the other Lenders (in such capacity, the "Agent"), FIRSTAR BANK, N.A.,
individually as a Lender and as syndication agent (the "Syndication Agent"),
CREDIT LYONNAIS NEW YORK BRANCH, individually as a Lender and as documentation
agent (the "Documentation Agent") and UNION PLANTERS BANK, N.A., individually as
a Lender and as CoAgent (the "CoAgent" and, together with the Agent, the
Documentation Agent and the Syndication Agent, the "Agents"). Capitalized terms
not defined herein shall have the meaning assigned to such terms in the Credit
Agreement.

                                  INTRODUCTION

         A. The Borrower, the Lenders, the Guarantors and the Agents are parties
to that certain Amended and Restated Credit Agreement dated effective as of the
Effective Date, as therein defined (the "Original Agreement"), which Original
Agreement has been amended by that certain Amendment to Amended and Restated
Credit Agreement (the "First Amendment") dated April 30, 2001, effective as of
the Effective Date (the Original Agreement, as amended by the First Amendment is
herein referred to as the "Credit Agreement").

         B. The Borrower has requested that the Agents and Lenders modify the
Credit Agreement to permit the issuance by Borrower of certain liquid yield
option notes.

         C. The Lenders and the Agents are agreeable to such requests upon the
terms and conditions herein stated.

         THEREFORE, the Borrower, the Guarantors, the Lenders and the Agents
hereby agree that the Credit Agreement is hereby amended and restated in its
entirety to read in the form of the Credit Agreement as it currently exists,
with amendments to certain sections thereof, as follows:

                                   ARTICLE I
                                CREDIT AGREEMENT

         Section 1.1 Definitions.

                  (a) All capitalized terms used herein and not otherwise
         defined shall have the meanings given in the Credit Agreement.

                  (b) A new definition of "LYONs" is hereby added in
         alphabetical order, as follows:

                  "LYONs" is defined in Section 6.11(ix).


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                  (c) The definition of "Consolidated Interest Expense" is
         hereby deleted and replaced with the following:

                  "Consolidated Interest Expense" means, for any Person, with
                  reference to any period, the actual interest expense of such
                  Person and its Subsidiaries calculated on a consolidated basis
                  for such period excluding any amortization of financing fees
                  incurred in connection with this Agreement and excluding any
                  non cash interest expense related to the LYONs (as defined
                  below).

         Section 1.2 Amendment to Section 6.11. A new part (ix) is hereby added
to Section 6.11, as follows:

                  (ix)     Indebtedness evidenced by those certain liquid yield
                           option notes due 2021 in an amount not in excess of
                           $790,000,000 in face value, more particularly
                           described in that certain Offering Memorandum dated
                           April 26, 2001, prepared by Merrill Lynch & Co., in
                           the form provided to the Agent (the "LYONs").

         Section 1.3 Amendment to Section 6.17. A new sentence is hereby added
to the end of Section 6.17 as follows:

                           Notwithstanding the foregoing, the Borrower may
                           voluntarily prepay principal or interest on its or
                           any of its Subsidiaries' Indebtedness existing on the
                           date hereof with the proceeds from the LYONs.

         Section 1.4 New Section 6.22.5. A new Section 6.22.5 is hereby added,
as follows:

                  6.22.5 LYONs. Only for purposes of calculating the ratio above
                  in Subsection 6.22.1, obligations of Borrower under the LYONs
                  shall not be included as Consolidated Total Debt.

         Section 1.5 New Sections 6.27, 6.28 and 6.29. New Sections 6.27, 6.28
and 6.29 are hereby added, as follows:

                  6.27. Payment on LYONs. Neither Borrower nor any of its
                  Subsidiaries shall prepay or redeem all or any portion of the
                  LYONs for cash, whether voluntarily or as may be required by
                  the holders of the LYONs.

                  6.28. LYONs Interest Expense. Neither Borrower nor any of its
                  Subsidiaries shall pay cash interest expense with respect to
                  the LYONs.

                  6.29. LYONs Indenture. Borrower shall not amend or agree to
                  any amendment of the indenture dated May 1, 2001 under which
                  the LYONs are issued.


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         Section 1.6 New Section 7.21. A new Section 7.21 is hereby added, as
follows:

                  7.21 The occurrence of a default or an event of default under
                  the indenture dated May 1, 2001 under which the LYONs are
                  issued or any other event which would allow all or any of the
                  holders of the LYONs to declare the LYONs to be immediately
                  due and payable.

         Section 1.7 No Waiver of Event of Default. The provisions hereof shall
not in any way be construed to waive, nor shall this Amendment in any way serve
as a waiver of any Default now or hereafter existing under the Credit Agreement
or other Loan Documents, except as expressly set forth herein.

                                   ARTICLE II
                           MISCELLANEOUS; RATIFICATION

         Section 2.1 Representations True; No Default. The Borrower and the
Guarantors represent and warrant, as applicable, that:

                  (a) The Borrower and the Guarantors represent and warrant that
         this Amendment has been duly authorized, executed and delivered on
         their behalf and the Credit Agreement as amended hereby, together with
         each other Loan Documents to which the Borrower and each of the
         Guarantors is a party, constitute valid and legally binding agreements
         of the Borrower and the Guarantors enforceable in accordance with their
         terms, except as enforceability thereof may be limited by bankruptcy,
         insolvency, fraudulent conveyance, fraudulent transfer, reorganization
         or moratorium or other similar law relating to creditors' rights and by
         general equitable principles which may limit the right to obtain
         equitable remedies (regardless of whether such enforceability is
         considered in a proceeding, in equity or at law);

                  (b) The Borrower represents and warrants that the
         representations and warranties of the Borrower contained in Article V
         of the Credit Agreement are true and correct in all material respects
         on and as of the date hereof as though made on and as of the date
         hereof, except to the extent such representations and warranties relate
         solely to an earlier date;

                  (c) The Guarantors represent and warrant that the
         representations and warranties of the Guarantors contained in the
         Guaranty are true and correct in all material respects on and as of the
         date hereof as though made on and as of the date hereof, except to the
         extent such representations and warranties relate solely to an earlier
         date; and

                  (d) The Borrower and the Guarantors represent and warrant that
         after giving effect to this Amendment, there has not occurred and is
         not continuing a Default or an event that with the passage of time
         would constitute a Default.

         Section 2.2 Ratification and Extension of Liens. The Credit Agreement,
the Notes and all other Loan Documents executed in connection therewith to which
the Borrower or any Guarantor is a party shall remain in full force and effect,
and all rights and powers created thereby or thereunder and under the other Loan
Documents to which the Borrower or any


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Guarantor is a party are in all respects ratified and confirmed. All liens
created by any Loan Document are hereby regranted by the Borrower and the
Guarantors to the Lenders as security for the Obligations. The Borrower and the
Guarantors agree that the obligations of the Borrower and the Guarantors under
the Credit Agreement, the Notes and the other Loan Documents to which the
Borrower or any Guarantor is a party are hereby brought forward, renewed and
extended.

         Section 2.3 Expenses, Additional Information. The Borrower shall pay to
the Agent all reasonable expenses incurred in connection with the negotiation
and execution of this Amendment. The Borrower and the Guarantors shall furnish
to the Agent all such other documents, consents and information relating to the
Borrower and the Guarantors as the Agent may reasonably require to accomplish
the purposes hereof.

         Section 2.4 Amendment Fee. The Borrower shall pay to the Agent, for the
ratable benefit of the Lenders that have delivered an executed copy of this
Amendment to the Agent no later than 12:00 noon Central Daylight Time on Friday,
April 27, an amendment fee equal to 10 basis points (each basis point equaling
one one-hundredth of one percent) multiplied times the Commitment of each such
Lender.

         Section 2.5 Miscellaneous Provisions.

                  (a) From and after the execution and delivery of this
         Amendment, the Credit Agreement shall be deemed to be amended and
         modified as herein provided, but, except as so amended and modified,
         the Credit Agreement and all other Loan Documents shall continue in
         full force and effect.

                  (b) The Credit Agreement and this Amendment shall be read and
         construed as one and the same instrument.

                  (c) Any reference in any Loan Document to the Credit Agreement
         shall be a reference to the Credit Agreement, as amended by this
         Amendment.

                  (d) This Amendment may be signed in any number of counterparts
         and by different parties in separate counterparts, each of which shall
         be deemed an original but all of which together shall constitute one
         and the same instrument.

                  (e) The headings herein shall be accorded no significance in
         interpreting this Amendment.

         Section 2.6 Binding Effect. This Amendment shall be binding upon and
inure to the benefit of the Borrower, the Guarantors, Agents and Lenders and the
successors and assigns of the Agent and Lenders. The Borrower and the Guarantors
shall not have the right to assign its rights hereunder or any interest herein.

         Section 2.7 Choice of Law. THIS AMENDMENT SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF ILLINOIS, EXCEPT TO THE
EXTENT THAT THE LAWS OF THE UNITED STATES OF AMERICA AND ANY RULES, REGULATIONS
OR ORDERS ISSUED OR


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PROMULGATED THEREUNDER APPLICABLE TO THE AFFAIRS AND TRANSACTIONS OF THE LENDERS
OTHERWISE PREEMPT ILLINOIS LAW, IN WHICH EVENT SUCH FEDERAL LAW SHALL CONTROL.


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                  EXECUTED to be effective as of the date first written above.

                                    THE SHAW GROUP INC.


                                    By:
                                             -----------------------------------
                                    Name:    Robert L. Belk
                                    Title:   Executive Vice President and
                                             Chief Financial Officer

                                    Address:

                                    8545 United Plaza Boulevard
                                    Baton Rouge, Louisiana 70809
                                    Attention:  Robert L. Belk
                                    Telephone: 225-932-2567
                                    Telecopy: 225-932-9146
                                    E-Mail: bob.belk@shawgrp.com


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                                   GUARANTORS:

                                   ACL Piping, Inc.
                                   Associated Valve, Inc.
                                   B.F. Shaw, Inc.
                                   C.B.P. Engineering Corp.
                                   Eagle Industries, Inc.
                                   Gulf Coast Equipment Rental, Inc.
                                   IRM/NAPTech Joint Venture, L.L.C.
                                   Lone Star Fabricators, Inc.
                                   NAPTech PS Corporation
                                   Prospect Industries (Holdings), Inc.
                                   SAON Properties, Inc.
                                   Secorp, Inc.
                                   Shaw Alloy Piping Products, Inc.
                                   Shaw Capital, Inc.
                                   Shaw Connex, Inc.
                                   Shaw Constructors, Inc.
                                   Shaw Energy Services, Inc.
                                   Shaw Fabricators, Inc.
                                   Shaw Fronek A/DE, Inc.
                                   Shaw Fronek Company, Inc.
                                   Shaw-Fronek Fabrication, Inc.
                                   Shaw Fronek Power Services, Inc.
                                   Shaw FVF, Inc.
                                   Shaw Global Energy Services, Inc.
                                   Shaw GRP of California
                                   Shaw Industrial Supply Co., Inc.
                                   Shaw International, Inc.
                                   Shaw Maintenance, Inc.
                                   Shaw Managed Services, Inc.
                                   Shaw Manufacturing and Services, Inc.
                                   Shaw NAPTech, Inc.
                                   Shaw Pipe Shields, Inc.
                                   Shaw Power Services, Inc.
                                   Shaw Process and Industrial Group, Inc.
                                   Shaw Process Fabricators, Inc.
                                   Shaw Services Inc.
                                   Shaw Sunland Fabricators, Inc.
                                   Shaw Word Industries Fabricators, Inc.
                                   Stone & Webster Holding One, Inc.
                                   Stone & Webster Holding Two, Inc.
                                   Stone & Webster, Inc.


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                                   SWINC Acquisition Four, Inc.
                                   SWINC Acquisition Five, L.L.C.
                                   Welding Technology and Supply Inc.
                                   Worldwide Industrial Constructors Inc.



                                   By:
                                            ------------------------------------
                                   Name:    Gary Graphia
                                   Title    Secretary


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                                    BANK ONE, NA,
                                    as Agent, as a Lender and as Issuer


                                    By:
                                             -----------------------------------
                                    Name:    John J. Zollinger, IV
                                    Title:   Associate Director

                                    Address:

                                    c/o Bank One Center, 910 Travis
                                    7th Floor
                                    Houston, Texas 77002
                                    Attention:        John J. Zollinger, IV
                                    Telephone:        713-751-6188
                                    Telecopy:         713-751-6777
                                    E-Mail: john_j_zollinger@bankone.com


                                    COMMITMENT:  $55,250,000


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                                    CREDIT LYONNAIS NEW YORK BRANCH,
                                    as Documentation Agent and as a Lender


                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $37,500,000



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                                    FIRSTAR BANK, N.A., as Syndication Agent and
                                    as a Lender


                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------



                                    COMMITMENT:  $40,000,000


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                                    UNION PLANTERS BANK, N.A.,
                                    as Co-Agent and as a Lender



                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $35,000,000


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                                    BNP PARIBAS HOUSTON AGENCY



                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $25,000,000


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                                    HARRIS TRUST & SAVINGS BANK



                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $18,750,000


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                                    WACHOVIA BANK, N.A.



                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $18,500,000


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                                    THE BANK OF NOVA SCOTIA


                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $15,000,000



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                                    THE MITSUBISHI TRUST & BANKING CORPORATION



                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $15,000,000


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                                    KBC BANK N.V.



                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $15,000,000



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                                    BANK HAPOALIM B.M., CHICAGO BRANCH



                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $10,000,000


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                                    CHANG HWA COMMERCIAL BANK, LTD.,
                                    NEW YORK BRANCH




                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $7,500,000


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                                    NATEXIS BANQUES POPULAIRES



                                    By:
                                             -----------------------------------
                                    Name:
                                             -----------------------------------
                                    Title:
                                             -----------------------------------


                                    COMMITMENT:  $7,500,000



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                                    BANC ONE CAPITAL MARKETS, INC.,
                                    as Lead Arranger and Sole Book Runner


                                    By:
                                           -------------------------------------
                                    Name:  John J. Zollinger, IV,
                                    Title: Associate Director

                                    Address:

                                    c/o Bank One Center, 910 Travis
                                    7th Floor
                                    Houston, Texas 77002
                                    Attention: John J. Zollinger, IV
                                    Telephone: (713) 751-6188
                                    Telecopy:   (713) 751-6777
                                    Email:  john_j_zollinger@bankone.com



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