UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15 (d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of report (Date of earliest event reported): November 13, 2018

NORTHWEST PIPELINE LLC

(Exact name of registrant as specified in its charter)

Registrant’s Telephone Number, Including Area Code: (801) 583-8800

Check the appropriate box below if the Form 8-K is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR 230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR 240.12b-2).

Emerging growth company  ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

On November 13, 2018, Northwest Pipeline LLC (the “Company”) issued a press release announcing that it has commenced an offer to exchange any and all of its $250 million in aggregate principal amount of outstanding 4.000 percent Senior Notes due 2027 that were originally issued in a private transaction on August 24, 2018 (the “Original Notes”) for an equal amount of its registered 4.000 percent Senior Notes due 2027 (the “Exchange Notes”). The Original Notes were an additional issuance of the Company’s $250 million aggregate principal amount of 4.000 percent Senior Notes due 2027 that were issued on April 3, 2017, all of which have been previously exchanged for notes that have been registered under the Securities Act of 1933, as amended (the “Act”). The exchange offer will expire at 5:00 p.m., New York City time, on December 12, 2018, unless extended

The terms of the Exchange Notes are identical in all material respects to those of the Original Notes, except that the Exchange Notes have been registered under the Act, and the transfer restrictions, registration rights and additional interest provisions relating to the Original Notes do not apply to the Exchange Notes. The purpose of the Exchange Offer is to fulfill the Company’s obligations under the registration rights agreement entered into in connection with the issuance of the Original Notes. The Company will not receive any proceeds from the exchange offer.

(d)    Exhibits.

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 hereunto duly authorized.

DATED: November 13, 2018