UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

OCI Partners LP

(Name of Issuer)

Common Units representing Limited Partner Interests

(Title of Class of Securities)

67091N108

(CUSIP Number)

Kevin Struve

Manager, OCIP Holding LLC

c/o OCI USA Inc.

(646) 589-6180

Copy to:

Brett E. Braden, Esq.

Latham & Watkins LLP

811 Main Street, Suite 3700

Houston, Texas 77002

Telephone: (713) 546-5300

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

April 17, 2015

(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 which is subject of this Schedule 13D, and is filing this statement because of Rule 13d-1(e), 13d-1(f) or 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 Rule 13d-7(b) for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of section 18 of the Securities Exchange Act of 1934 (the “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).

2

3

4

This Amendment No. 1 to Schedule 13D (“Amendment No. 1”) amends the Schedule 13D originally filed with the Securities and Exchange Commission (the “Commission”) on November 20, 2014 (the “Original Schedule”). Except as specifically amended by this Amendment No. 1, each Item of the Original Schedule remains unchanged.

This Schedule 13D relates to common units representing limited partner interests (the “Common Units”) of OCI Partners LP, a Delaware limited partnership (the “Issuer”). The Issuer’s principal executive office is located at 5470 N. Twin City Highway, Nederland, Texas 77627.

Item 3 of the Original Schedule is amended and restated in its entirety as follows:

OCIP Holding and the Issuer entered into a Contribution Agreement, dated as of November 10, 2014 (the “2014 Contribution Agreement”), pursuant to which OCIP Holding contributed $60.0 million as a capital contribution to the Issuer (the “2014 Capital Contribution”), and the Issuer issued 2,995,372 Common Units (the “2014 Contribution Units”) to OCIP Holding in exchange for the 2014 Capital Contribution. The price per unit of each 2014 Contribution Unit was $20.0309, which was the volume-weighted average trading price of the Issuer’s Common Units on the New York Stock Exchange, calculated over the consecutive 20-trading day period ending on the close of trading on the trading day immediately prior to the transaction date. Prior to execution of the 2014 Contribution Agreement, OCI USA contributed $60.0 million from its working capital as a capital contribution to Pluto Holding Limited (“Pluto”), a wholly owned subsidiary of OCI USA, who in turn subsequently contributed $60.0 million from its working capital as a capital contribution to its subsidiary, OCIP Holding. The funds contributed by Pluto were used by OCIP Holding for the 2014 Capital Contribution. The 2014 Capital Contribution constituted a draw by the Issuer under an equity commitment letter, dated November 22, 2013 (the “Equity Commitment Letter”), between OCI USA and the Partnership that provides for up to a $100.0 million equity commitment by OCI USA available to be drawn by the Issuer in certain circumstances.

5

OCIP Holding and the Issuer subsequently entered into a Contribution Agreement, dated as of April 17, 2015 (the “2015 Contribution Agreement” and, together with the 2014 Contribution Agreement, the “Contribution Agreements”), pursuant to which OCIP Holding contributed $60.0 million as a capital contribution to the Issuer (the “2015 Capital Contribution” and, together with the 2014 Capital Contribution, the “Capital Contributions”), and the Issuer issued 3,502,218 Common Units (the “2015 Contribution Units”) to OCIP Holding in exchange for the 2015 Capital Contribution. The price per unit of each 2015 Contribution Unit was $ 17.132, which was the volume-weighted average trading price of the Issuer’s Common Units on the New York Stock Exchange, calculated over the consecutive 21-trading day period ending on the close of trading on the trading day immediately prior to the transaction date. Prior to execution of the 2015 Contribution Agreement, OCI USA contributed $60.0 million from its working capital as a capital contribution to Pluto, who in turn subsequently contributed $60.0 million from its working capital as a capital contribution to its subsidiary, OCIP Holding. The funds contributed by Pluto were used by OCIP Holding for the 2015 Capital Contribution. The 2015 Capital Contribution constituted (i) a draw of $40.0 million by the Issuer on the remaining balance available under the Equity Commitment Letter and (ii) an additional cash contribution by OCI USA, through OCIP Holding, to the capital of the Issuer in the amount of $20.0 million.

References to, and descriptions of, the 2014 Contribution Agreement and the 2015 Contribution Agreement as set forth in this Item 3 and elsewhere in this Schedule 13D are qualified in their entirety by reference to the 2014 Contribution Agreement filed as Exhibit 10.1 to the Issuer’s Current Report on Form 8-K filed with the Securities and Exchange Commission on November 12, 2014 and to the 2015 Contribution Agreement filed as Exhibit 10.1 to the Issuer’s Current Report on Form 8-K filed with the Securities and Exchange Commission on April 23, 2015, respectively.

Item 4 of the Original Schedule is amended and restated in its entirety as follows:

The Reporting Persons acquired the Common Units described in this Schedule 13D in exchange for the Capital Contributions in order to fund capital expenditures and other costs and expenses which have been or will be incurred by the Issuer in connection with a debottlenecking project at its methanol and ammonia production facility.

The Reporting Persons acquired the Common Units described in this Schedule 13D for investment purposes and they intend to review their investments in the Issuer on a continuing basis. Any actions the Reporting Persons might undertake will be dependent upon the Reporting Persons’ review of numerous factors, including, but not limited to: an ongoing evaluation of the Issuer’s business, financial condition, operations and prospects; price levels of the Issuer’s Common Units; general market, industry and economic conditions; the relative attractiveness of alternative business and investment opportunities; and other future developments.

The Reporting Persons may, at any time and from time to time, acquire additional Common Units of the Issuer, or retain or sell all or a portion of the Common Units then held, in the open market or in privately negotiated transactions. In addition, the Reporting Persons or their designees to the board of directors of the Issuer’s general partner may engage in discussions with management, the board of directors, and unitholders of the Issuer and other relevant parties or encourage such persons to consider or explore extraordinary corporate transactions, such as: a merger; sales or acquisitions of assets or businesses; changes to the capitalization or distribution policy of the Issuer; or other material changes to the Issuer’s business or organizational structure.

Other than as described above, none of the Reporting Persons currently has any plans or proposals that relate to, or would result in, any of the matters listed in Items 4(a)–(j) of Schedule 13D, although, depending on the factors discussed herein, the Reporting Persons may change their purpose or formulate different plans or proposals with respect thereto at any time.

6

Item 5 of the Original Schedule is amended and restated in its entirety as follows:

OCIP Holding, the direct owner the securities reported herein, is a wholly owned subsidiary of OCI USA. OCI NV and OCI USA, and their direct and indirect subsidiaries, may be deemed to indirectly own the securities of the Issuer held by OCIP Holding, but each disclaims beneficial ownership except to the extent of its respective pecuniary interest therein.

The Issuer is managed by the directors and executive officers of its general partner, OCI GP LLC (the “General Partner”). OCI USA has the right to appoint the board of directors and executive officers of the General Partner and the managing member of OCIP Holding.

OCI NV, by majority vote of its board of directors, has the power to vote and dispose of the Common Units held by OCIP Holding. As such, no individual director is deemed to hold any beneficial ownership in the Common Units.

Apart from the Contribution Agreements and Equity Commitment Letter described in Item 3, none of the Reporting Persons nor any person named in Schedule I have entered into any contracts, arrangements, understandings or relationships with respect to securities of the Issuer.

7

8

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: April 23, 2015

JOINT FILING AGREEMENT

In accordance with Rule 13(d)-1(k)(1) under the Securities Exchange Act of 1934, as amended, the undersigned hereby agree to the joint filing with each other of the attached statement on Schedule 13D and to all amendments to such statement.

IN WITNESS WHEREOF, the undersigned have executed this Joint Filing Agreement as of April 23, 2015.

Schedule I

Information regarding each director and executive officer of the Reporting Persons is set forth below.

12