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EXHIBIT 10.23

SIXTH AMENDMENT TO LOAN AGREEMENT

    This amendment to Loan Agreement ("Amendment") is made as of August 31, 2000
by and among the following parties:

    Bank of America, N.A., formerly known as Bank of America National Trust and
Savings Association ("Bank of America" and a "Lender")

    U.S. Bank National Association ("U.S. Bank" and a "Lender")

    Bank of America, N.A., formerly known as Bank of America National Trust and
Savings Association, in its capacity as Agent ("Agent")

    Each of the several financial institutions which subsequently becomes party
to the Loan Agreement pursuant to Section 11.7 (each individually a "Lender")

    Northwest Pipe Company, an Oregon corporation ("Borrower")

R E C I T A L S

    A.  The Borrower, the Lenders and the Agent are parties to that certain
Amended and Restated Loan Agreement dated as of June 30, 1998, as amended as of
December 23, 1998, June 16, 1999, November 30, 1999, December 30, 1999 and
May 11, 2000, and as the same may be further amended, modified or extended from
time to time (the "Loan Agreement") and the related Loan Documents described
therein.

    B.  The parties desire to amend the Loan Agreement as set forth below:

    NOW, THEREFORE, the parties agree as follows:

A G R E E M E N T

    1.  Definitions.  Capitalized terms used herein and not otherwise defined
shall have the meaning given in the Loan Agreement.

    2.  Amendment to Section 1.1.  Section 1.1 of the Loan Agreement is amended
by revising the definition of "Temporary Supplemental Revolving Loan Commitment"
as follows:

"Temporary Supplemental Revolving Loan Commitment" means Ten Million Dollars
($10,000,000.00) until September 30, 2000, after which there shall be no
Temporary Supplemental Revolving Loan Commitment.

    Amendment to Section 1.1. Section 1.1 of the Loan Agreement is amended by
revising the following definition of "Temporary Supplemental Revolving Loan
Maturity Date" as follows:

"Temporary Supplemental Revolving Loan Maturity Date" means September 30, 2000.

    3.  Amendment to Section 12.1.  Section 12.1 of the Loan Agreement is
amended by changing the ending date of the period during which each lender
agrees to make Temporary Supplemental Revolving Loans to September 30, 2000.

    4.  No Further Amendment.  Except as expressly modified by this Amendment,
the Loan Agreement and the other Loan Documents shall remain unmodified and in
full force and effect and the parties hereby ratify their respective obligations
thereunder. Without limiting the foregoing, the Borrower expressly reaffirms and
ratifies its obligation to pay or reimburse the Agent and the Lender on request
for all reasonable expenses, including legal fees, actually incurred by the
Agent or such Lender in connection with the preparation of this Amendment, any
other amendment documents, and the closing of the transactions contemplated
hereby and thereby.

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    5.  Miscellaneous.  

    (a) Entire Agreement.  This Amendment comprises the entire agreement of the
parties with respect to the subject matter hereof and supersedes all prior oral
or written agreements, representations or commitments.

    (b) Counterparts.  This Amendment may be executed in any number of
counterparts and by different parties hereto in separate counterparts, each of
which when so executed shall be deemed to be an original, and all of which taken
together shall constitute one and the same Amendment.

    (c) Governing Law.  This Amendment and the other agreements provided for
herein and the rights and obligations of the parties hereto and thereto shall be
construed and interpreted in accordance with the laws of the State of Oregon.

    (d) Certain Agreements Not Enforceable.  UNDER OREGON LAW, MOST AGREEMENTS,
PROMISES AND COMMITMENTS MADE BY THE LENDERS AFTER OCTOBER 3, 1989, CONCERNING
LOANS AND OTHER CREDIT EXTENSIONS WHICH ARE NOT FOR PERSONAL, FAMILY OR
HOUSEHOLD PURPOSES OR SECURED SOLELY BY THE BORROWER'S RESIDENCE MUST BE IN
WRITING, EXPRESS CONSIDERATION, AND BE SIGNED BY THE LENDERS TO BE ENFORCEABLE.

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    EXECUTED AND DELIVERED by the duly authorized officers of the parties as of
the date first above written.

BORROWER:   NORTHWEST PIPE COMPANY  
   
   
By: BRIAN DUNHAM
Its: PRESIDENT AND CHIEF OPERATING OFFICER     Address:   200 S.W. Market
Street, Suite 1800
Portland OR 97201
Fax No. (503) 240-6615  
LENDER:  
   
BANK OF AMERICA, N.A.  
   
   
By: ED KLUSS
Its: VICE PRESIDENT     Address:   Commercial Banking
121 SW Morrison Street, Suite 1700
Portland OR 97204
Fax No. (503) 275-1391
Attn: Larry C. Ellis  
   
   
U.S. BANK NATIONAL ASSOCIATION  
   
   
By: TIMOTHY G. STEMPEL
Its: SENIOR VICE PRESIDENT     Address:   Oregon Corporate Banking, T-4
111 SW Fifth Avenue, Suite 400
Portland OR 97208
Fax No. (503) 275-7290
Attn: Stephen Mitchell  
AGENT:  
   
BANK OF AMERICA, N.A.  
   
   
By: DORA A. BROWN
Its: VICE PRESIDENT  
   
      Address:   Agency Services
701 Fifth Avenue, Floor 16
Seattle WA 98104
Fax No. (206) 358-0971
Attn: Dora A. Brown

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SIXTH AMENDMENT TO LOAN AGREEMENT
R E C I T A L S
A G R E E M E N T