<SEC-DOCUMENT>0001445525-13-000028.txt : 20130829
<SEC-HEADER>0001445525-13-000028.hdr.sgml : 20130829
<ACCEPTANCE-DATETIME>20130829172121
ACCESSION NUMBER:		0001445525-13-000028
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20130827
FILED AS OF DATE:		20130829
DATE AS OF CHANGE:		20130829

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			NORTHWEST PIPE CO
		CENTRAL INDEX KEY:			0001001385
		STANDARD INDUSTRIAL CLASSIFICATION:	STEEL PIPE & TUBES [3317]
		IRS NUMBER:				930557988
		STATE OF INCORPORATION:			OR
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		5721 SE COLUMBIA WAY
		STREET 2:		SUITE 200
		CITY:			VANCOUVER
		STATE:			WA
		ZIP:			98661
		BUSINESS PHONE:		3603976250

	MAIL ADDRESS:	
		STREET 1:		5721 SE COLUMBIA WAY
		STREET 2:		SUITE 200
		CITY:			VANCOUVER
		STATE:			WA
		ZIP:			98661

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Dana Martin W
		CENTRAL INDEX KEY:			0001585254

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-27140
		FILM NUMBER:		131070084

	MAIL ADDRESS:	
		STREET 1:		5721 SE COLUMBIA WAY SUITE 200
		CITY:			VANCOUVER
		STATE:			WA
		ZIP:			98661
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
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<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
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<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2013-08-27</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001001385</issuerCik>
        <issuerName>NORTHWEST PIPE CO</issuerName>
        <issuerTradingSymbol>NWPX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001585254</rptOwnerCik>
            <rptOwnerName>Dana Martin W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>5721 SE COLUMBIA WAY SUITE 200</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>VANCOUVER</rptOwnerCity>
            <rptOwnerState>WA</rptOwnerState>
            <rptOwnerZipCode>98661</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Exec VP, Tubular Products</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4159</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
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            <securityTitle>
                <value>Restricted Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
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            <exerciseDate>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
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                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
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            <underlyingSecurity>
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                </underlyingSecurityTitle>
                <underlyingSecurityShares>
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                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
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                <natureOfOwnership>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
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                </underlyingSecurityTitle>
                <underlyingSecurityShares>
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            </underlyingSecurity>
            <ownershipNature>
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        </derivativeHolding>
        <derivativeHolding>
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        <derivativeHolding>
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                <underlyingSecurityTitle>
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                <directOrIndirectOwnership>
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        </derivativeHolding>
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            <securityTitle>
                <value>Performance Shares</value>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2293</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Performance Shares</value>
            </securityTitle>
            <conversionOrExercisePrice>
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            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F8"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3139</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each Restricted Stock Unit represents a contingent right to receive one share of Northwest Pipe Company common stock.</footnote>
        <footnote id="F2">The Restricted Stock Units vest on January 1, 2014.</footnote>
        <footnote id="F3">The Restricted Stock Units vest in installments as follows: 1/2 on January 1, 2014 and 1/2 on January 1, 2015.</footnote>
        <footnote id="F4">The Restricted Stock Units vest in installments as follows: 1/3 on January 15, 2014, 1/3 on January 15, 2015 and 1/3 or January 15, 2016.</footnote>
        <footnote id="F5">The Performance Shares vest on January 1, 2014 in an amount ranging from 0-200% to the extent such Performance Shares are earned.  Performance Shares are earned based on Northwest Pipe Company's total shareholder return for 2011-2013 relative to the total shareholder return of a peer group over the same period.</footnote>
        <footnote id="F6">The Performance Shares vest on January 1, 2014 in an amount ranging from 0-200% to the extent such Performance Shares are earned.  Performance Shares are earned based on Northwest Pipe Company's total shareholder return for 2012-2013 relative to the total shareholder return of a peer group over the same period.</footnote>
        <footnote id="F7">The Performance Shares vest on January 1, 2015 in an amount ranging from 0-200% to the extent such Performance Shares are earned.  Performance Shares are earned based on Northwest Pipe Company's total shareholder return for 2012-2014 relative to the total shareholder return of a peer group over the same period.</footnote>
        <footnote id="F8">The Performance Shares vest on January 15, 2016 in an amount ranging from 0-200% to the extent such Performance Shares are earned.  Performance Shares are earned based on Northwest Pipe Company's total shareholder return for 2013-2015 relative to the total shareholder return of a peer group over the same period.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Martin Dana</signatureName>
        <signatureDate>2013-08-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
