Exhibit 3.16


                         PREFERRED PIPE PRODUCTS, INC.

                            An Oklahoma Corporation

                                   BY-LAWS*



                                   ARTICLE I

                                  SHAREHOLDERS

     Section 1.1 Annual Meeting.

     An annual meeting of shareholders for the purpose of electing directors
and of transacting such other business as may come before it shall be held each
year at such date, time, and place, either within or without the State of
Oklahoma, as may be specified by the Board of Directors.

     Section 1.2 Special Meetings.

     Special meetings of shareholders for any purpose or purposes may be held
at any time upon call of the Chairman of the Board, if any, the President, the
Secretary, or a majority of the Board of Directors, at such time and place
either within or without the State of Oklahoma as may be stated in the notice.
A special meeting of shareholders shall be called by the President or the
Secretary upon the written request, stating time, place, and the purpose or
purposes of the meeting, of shareholders who together own of record a majority
of the outstanding stock of all classes entitled to vote at such meeting.

     Section 1.3 Notice of Meetings.

     Written notice of shareholders meetings, stating the place, date, and hour
thereof, and, in the case of a special meeting, the purpose or purposes for
which the meeting is called, shall be given by the Chairman of the Board, if
any, the President, any Vice President, the Secretary, or an Assistant
Secretary, to each

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     *AS AMENDED AND RESTATED ON SEPTEMBER 19, 1990





stockholder entitled to vote thereat at least ten (10) days but not more than
sixty (60) days before the date of the meeting, unless a different period is
prescribed by law.

     Section 1.4 Quorum.

     Except as otherwise provided by law or in the Certificate of Incorporation
or these By-Laws, at any meeting of shareholders, the holders of a majority of
the outstanding shares of each class of stock entitled to vote at the meeting
shall be present or represented by proxy in order to constitute a quorum for
the transaction of any business. In the absence of a quorum, a majority in
interest of the shareholders present who are entitled at the time to vote or
the chairman of the meeting may adjourn the meeting from time to time in the
manner provided in Section 1.5 of these By-Laws until a quorum shall attend.

     Section 1.5 Adjournment.

     Any meeting of shareholders, annual or special, may adjourn from time to
time to reconvene at the same or some other place, and notice need not be given
of any such adjourned meeting if the time and place thereof are announced at
the meeting at which the adjournment was taken. At the adjourned meeting, the
Corporation may transact any business which might have been transacted at the
original meeting. If the adjournment is for more than thirty (30) days, or if
after the adjournment, a new record date is fixed for the adjourned meeting, a
notice of the adjourned meeting shall be given to each shareholder of record
entitled to vote at the meeting.

     Section 1.6 Organization.

     The Chairman of the Board, if any, or in his absence the President, or in
their absence any Vice President, shall call to order meetings of shareholders
and shall act as chairman of such meetings. The Board of Directors or, if the
Board fails to act, the shareholders may appoint any shareholder, director, or
officer of the Corporation to act as chairman of any meeting in the absence of
the Chairman of the Board, the President, and all Vice Presidents.

     The Secretary of the Corporation shall act as secretary of all meetings of
shareholders, but, in the absence of the Secretary, the chairman of the meeting
may appoint any other person to act as secretary of the meeting.

     Section 1.7 Voting.

     Except as otherwise provided by law or in the Certificate of Incorporation
or these By-Laws and except for the election of directors, at any meeting duly
called and held at which a quorum is present, a majority of the votes cast at
such


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meeting upon a given question by the holders of outstanding shares of stock of
all classes of stock of the Corporation entitled to vote thereon who are
present in person or by proxy shall decide such question. At any meeting duly
called and held for the election of directors at which a quorum is present,
directors shall be elected by a plurality of the votes cast by the holders
(acting as such) of shares of stock of the Corporation entitled to elect such
directors.

                                   ARTICLE II

                               BOARD OF DIRECTORS

     Section 2.1 Number and Term of Office.

     The business, property, and affairs of the Corporation shall be managed by
or under the direction of a Board of four (4) directors provided, however, that
the number of directors may be increased to five (5) by vote of the holders of
outstanding shares of stock of the Corporation entitled to vote thereon. The
directors shall be elected by the holders of shares entitled to vote thereon at
the annual meeting of shareholders, and each shall serve (subject to the
provisions of Article IV) until the first to occur of (a) the next succeeding
annual meeting of shareholders and (b) his removal by a vote of shareholders;
and until his respective successor has been elected and qualified.

     Section 2.2 Chairman of the Board.

     The directors may elect one of their members to be Chairman of the Board
of Directors. The Chairman shall be subject to the control of and may be
removed by the Board of Directors. He shall perform such duties as may from
time to time be assigned to him by the Board.

     Section 2.3 Meetings.

     The annual meeting of the Board of Directors, for the election of officers
and the transaction of such other business as may come before the meeting,
shall be held without notice at the same place as, and immediately following,
the annual meeting of the shareholders.

     Regular meetings of the Board of Directors may be held without notice at
such time and place as shall from time to time be determined by the Board.

     Special meetings of the Board of Directors shall be held at such time and
place as shall be designated in the notice of the meeting whenever called by
the Chairman of the Board, the President or by a majority of the directors then
in the office.


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     Section 2.4 Notice of Special Meetings.

     The Secretary, or in his absence, any other officer of the Corporation,
shall give each director notice of the time and place of holding of special
meetings of the Board of Directors by mail at least five (5) days before the
meeting, or by telegram, cable, radiogram, or personal service at least three
(3) days before the meeting. Unless otherwise stated in the notice thereof, any
and all business may be transacted at any meeting without specification of such
business in the notice.

     Section 2.5 Quorum and Organization of Meetings.

     A majority of the total number of members of the Board of Directors
authorized under Section 2.1 from time to time shall constitute a quorum for
the transaction of business, but, if at any meeting of the Board of Directors
(whether or not adjourned from a previous meeting) there shall be less than a
quorum present, a majority of those present may adjourn the meeting to another
time and place, and the meeting may be held as adjourned without further notice
or waiver if a quorum is then present. Except as otherwise provided by law or
in the Certificate of Incorporation or these By-Laws, a majority of the total
number of the members of the Board of Directors authorized under Section 2.1
from time to time shall be required in order to decide any question brought
before such meeting. Meetings shall be presided over by the Chairman of the
Board, if any, or in his absence by the President, or in the absence of both by
such other person as the directors may select. The Secretary of the Corporation
shall act as secretary of the meeting, but in his absence the chairman of the
meeting may appoint any person to act as secretary of the meeting.

     Section 2.6 Committees.

     The Board of Directors may, by resolution passed by a majority of the
whole Board, designate one or more committees, each committee to consist of one
or more of the directors of the Corporation. The Board may designate one or
more directors as alternate members of any committee, who may replace any
absent or disqualified member at any meeting of the committee. In the absence
or disqualification of a member of a committee, the member or members thereof
present at any meeting and not disqualified as members of a committee and not
disqualified from voting, whether or not he or they constitute a quorum, may
unanimously appoint another member of the Board of Directors to act at the
meeting in place of any such absent or disqualified member. Any such committee,
to the extent provided in the resolution of the Board of Directors, shall have
and may exercise all the powers and authority of the Board of Directors in the
management of the business, property, and affairs of the Corporation, and may
authorize the seal of the Corporation to be affixed to all papers which may
require it; but no such committee shall have power or authority in reference to
amending the Certificate of Incorporation of the Corporation, (except that a
committee may,


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to the extent authorized in the resolution or resolutions providing for the
issuance of shares of stock adopted by the Board of Directors pursuant to
authority expressly granted to the Board of Directors by the Corporations'
Certificate of Incorporation, (ix) any of the preferences or rights of such
shares relating to dividends, redemption, dissolution, any distribution of
assets of the Corporation, or the conversion into, or the exchange of such
shares for, shares of any other class or classes or any other series of the
same or any other class or classes of stock of the Corporation), adopting an
agreement of merger or consolidation under Section 1081 or 1082 of the Oklahoma
General Corporation Act, recommending to the shareholders the sale, lease, or
exchange of all or substantially all of the Corporations, property and assets,
recommending to the shareholders a dissolution of the Corporation or a
revocation of dissolution, or amending these By-Laws; and, unless the
resolution expressly so provided, no such committee shall have the power or
authority to declare a dividend, to authorize the issuance of stock, or to
adopt a certificate of ownership and merger pursuant to Section 1083 of the
Oklahoma General Corporation Act. Each committee which may be established by
the Board of Directors pursuant to these By-Laws may fix its own rules and
procedures. Notice of meetings of committees, other than of regular meetings
provided for by the rules, shall be given to committee members. All action
taken by committees shall be recorded in minutes of the meetings.

     Section 2.7 Action Without Meetings.

     Nothing contained in these By-Laws shall be deemed to restrict the power
of members of the Board of Directors or of any committee designated by the
Board to take any action required or permitted to be taken by them without a
meeting.

     Section 2.8 Telephone Meetings.

     Nothing contained in these By-Laws shall be deemed to restrict the power
of members of the Board of Directors, or any committee designated by the Board,
to participate in a meeting of the Board, or committee, by means of conference
telephone or similar communications equipment by means of which all persons
participating in the meeting can hear each other.

                                  ARTICLE III

                                    OFFICERS

     Section 3.1 Executive Officers.

     The executive officers of the Corporation shall be a President, one or
more Vice Presidents, a Treasurer, and a Secretary, each of whom shall be
elected by


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the Board of Directors. The Board of Directors may elect or appoint such other
officers (including a Controller and one or more Assistant Treasurers and
Assistant Secretaries) as it may deem necessary or desirable. Each officer
shall hold office for such term as may be prescribed by the Board of Directors
from time to time. Any person may hold at one time two or more offices.

     Section 3.2 Powers and Duties.

     The Chairman of the Board, if any, or, if his absence, the President,
shall preside at all meetings of the shareholders and of the Board of
Directors. The President shall be the chief executive officer of the
Corporation. In the absence of the President, a Vice President appointed by the
President or, if the President fails to make such appointment, by the Board,
shall perform all the duties of the President. The officers and agents of the
Corporation shall each have such powers and authority and shall perform such
duties in the management of the business, property, and affairs of the
Corporation as generally pertain to their respective offices, as well as such
power and authorities and such duties as from time to time may be prescribed by
the Board of Directors.

                                   ARTICLE IV

                     RESIGNATIONS, REMOVALS, AND VACANCIES

     Section 4.1 Resignations.

     Any director or officer of the Corporation, or any member of any
committee, may resign at any time by giving written notice to the Board of
Directors, the President, or the Secretary of the corporation. Any such
resignation shall take effect at the time specified therein or, if the time be
not specified therein, then upon receipt thereof. The acceptance of such
resignation shall not be necessary to make it effective.

     Section 4.2 Removals.

     The Board of Directors, by a vote of not less than a majority of the
entire Board, at any meeting thereof, or by written consent, at any time, may,
to the extent permitted by law, remove with or without cause from office or
terminate the employment of any officer or member of any committee and may,
with or without cause, disband any committee. Any director or the entire Board
of Directors may be removed, with or without cause, by the holders of a
majority of the shares entitled at the time to vote at an election of
directors.


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     Section 4.3 Vacancies.

     Any vacancy in the office of any officer through death, resignation,
removal, disqualification, or other cause may be filled at any time by the
directors. Any vacancy in the office of any director through death,
resignation, removal, disqualification, or other cause, and any additional
directorship resulting from an increase in the number of directors, may only be
filled by the shareholders who are at the time entitled to vote at an election
of directors, and, subject to the provisions of this Article IV, the person so
chosen shall hold office until his successor shall have been elected and
qualified; or, if the person so chosen is a director elected to fill a vacancy,
he shall (subject to the provisions of this Article IV) hold office for the
unexpired term of his predecessor.

                                   ARTICLE V

                                 CAPITAL STOCK

     Section 5.1 Stock Certificates.

     The certificates for shares of the capital stock of the Corporation shall
be in such form as shall be prescribed by law and approved, from time to time,
by the Board of Directors.

     Section 5.2 Transfer of Shares.

     Shares of the capital stock of the Corporation may be transferred on the
books of the Corporation only by the holder of such shares or by his duly
authorized attorney, upon the surrender to the Corporation or its transfer
agent of the certificate representing such stock properly endorsed.

     Section 5.3 Fixing Record Date.

     In order that the Corporation may determine the shareholders entitled to
notice of or to vote at any meeting of shareholders or any adjournment thereof
or to express consent to corporate action in writing without a meeting, or
entitled to received payment of any dividend or their distribution or allotment
of any rights, or entitled to exercise any rights in respect of any change,
conversion, or exchange of stock, or for the purpose of any other lawful
action, the Board of Directors may fix, in advance, a record date, which,
unless otherwise provided by law, shall not be more than sixty (60) nor less
than ten (10) days before the date of such meeting, nor more than sixty (60)
days prior to any other actions.

     Section 5.4 Lost Certificates.

     The Board of Directors or any transfer agent of the Corporation may direct
a new certificate or certificates representing stock of the Corporation to be
issued in place of any certificate or certificates theretofore issued by the
Corporation,


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alleged to have been lost, stolen, or destroyed, upon the making of an
affidavit of that fact by the person claiming the certificate to be lost,
stolen, or destroyed. When authorizing such issue of a new certificate or
certificates, the Board of Directors (or any transfer agent of the Corporation
authorized to do so by a resolution of the Board of Directors) may, in its
discretion and as a condition precedent to the issuance thereof, require the
owner of such lost, stolen, or destroyed certificate or certificate, or his
legal representative, to give the Corporation a bond in such sum as the Board
of Directors (or any transfer agent so authorized) shall direct to indemnify
the Corporation against any claim that may be made against the Corporation with
respect to the certificate alleged to have been lost, stolen, or destroyed or
the issuance of such new certificates, and such requirement may be general or
confined to specific instances.

     Section 5.5 Regulations.

     The Board of Directors shall have power and authority to make all such
rules and regulations as it may deem expedient concerning the issuance,
transfer, registration, cancellation, and replacement of certificates
representing stock of the Corporation.

                                   ARTICLE VI

                                 MISCELLANEOUS

     Section 6.1 Corporate Seal.

     The corporate seal shall have inscribed thereon the name of the
Corporation and shall be in such form as may be approved from time to time by
the Board of Directors.

     Section 6.2 Fiscal Year.

     The fiscal year of the Corporation shall begin on the first day of March
in each year and terminate on the last day of February in each succeeding year.

     Section 6.3 Notices and Waivers Thereof.

     Whenever any notice whatever is required by law, the Certificate of
Incorporation, or these By-Laws to be given to any shareholder, director, or
officer, such notice, except as otherwise provided by law, may be given
personally, or by mail, or, in the case of directors or officers, by telegram,
cable, or radiogram, addressed to such address as appears on the books of the
Corporation. Any notice given by telegram, cable, or radiogram shall be deemed
to have been given when it shall have been delivered for transmission and any
notice given by mail shall be deemed to have been given when it shall have been


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deposited in the United States mail with postage thereon prepaid. Whenever any
notice is required to be given by law, the Certificate of Incorporation, or
these ByLaws, a written waiver thereof, signed by the person entitled to such
notice, whether before or after the meeting or the time stated therein, shall
be deemed equivalent in all respects to such notice to the full extent
permitted by law.

     Section 6.4 Stock of Other Corporations or Other Interests.

     Unless otherwise ordered by the Board of Directors, the President, the
Secretary, and such attorneys or agents of the Corporation as may be from time
to time authorized by the Board of Directors or the President, shall have full
power and authority on behalf of this Corporation to attend and to act and vote
in person or by proxy at any meeting of the holders of securities of any
corporations or other entity in which this Corporation may own or hold shares
or other securities, and at such meetings shall possess and may exercise all
the rights and powers incident to the ownership of such shares or other
securities which this Corporation, as the owner of holder thereof, might have
possessed and exercised if present. The President, the Secretary, or such
attorneys or agents, may also execute and deliver on behalf of the corporation
powers of attorney, proxies, consents, waivers, and other instruments relating
to the share or securities owned or held by this Corporation.

                                  ARTICLE VII

                                   AMENDMENTS

     The holders of shares entitled at the time to vote for the election of
directors shall have power to adopt, amend, or repeal the By-Laws of the
Corporation by vote of not less than a majority of such shares, and except as
otherwise provided by law, the Board of Directors shall have power equal in all
respects to that of the shareholders to adopt, amend, or repeal the By-Laws by
vote of not less than a majority of the entire Board. However, any By-Laws
adopted by the Board may be amended or repealed by vote of the holders of a
majority of the shares entitled at the time to vote for the election of
directors.

     ADOPTED AND APPROVED THIS 19th DAY OF SEPTEMBER, 1990.

                                         By: /s/ Kevin Eagleton
                                            -------------------------------
                                            Kevin Eagleton, President

ATTEST:

/s/ Mark Barbeau
- ------------------------------
Mark Barbeau, Secretary


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