UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM SD

SPECIALIZED DISCLOSURE REPORT

NGL ENERGY PARTNERS LP

(Exact name of registrant as specified in its charter)

H. Michael Krimbill

Chief Executive Officer of NGL Energy Holdings LLC, the general partner of

NGL Energy Partners LP

(918) 481-1119

(Name and telephone number, including
area code, of the person to contact in connection with this report.)

Check the appropriate box to indicate the rule pursuant to which this form is being filed, and provide the period to which the information in this form applies:

x Rule 13p-1 under the Securities Exchange Act (17 CFR 240.13p-1) for the reporting period from January 1 to December 31, 2014.

Section 1 — Conflict Minerals Disclosure

Item 1.01 — Conflict Minerals Disclosure and Report

In accordance with Rule 13p-1 under the Securities Exchange Act of 1934 (“Rule 13p-1”), NGL Energy Partners LP has filed this Specialized Disclosure Form (“Form SD”) and the associated Conflict Minerals Report and both reports are posted to a publicly available Internet site at: www.nglenergypartners.com/investor-relations/sec-filings/.

Item 1.02 — Exhibit

The Conflict Minerals Report required by Items 1.01 and 1.02 is filed as Exhibit 1.01 to this Form SD.

Section 2 — Exhibits

Item 2.01 — Exhibits

Exhibit 1.01 — Conflict Minerals Report dated May 29, 2015.

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this Report to be signed on its behalf by the undersigned thereunto duly authorized.

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EXHIBIT INDEX

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