The ordinance authorizing such refunding revenue bonds shall prescribe all the details thereof and the bonds shall be in such form and denomination, payable at such places, bear such date and be executed by such officials as may be provided in the bond ordinance. The ordinance also shall determine the period of usefulness of the utility. The refunding revenue bonds shall mature within the determined period of usefulness of the utility and shall mature, in any event, within not to exceed 40 years from their date, and may be made callable on any interest payment date at a price of par and accrued interest, after notice shall be given by publication or otherwise at any time or times and in the manner as may be provided for in the bond ordinance.
     The ordinance may contain such covenants and restrictions upon the issuance of additional refunding revenue bonds, or revenue bonds for the improvement and extension of such utility or facility as may be deemed necessary or advisable for the assurance of the payment of the refunding revenue bonds thereby authorized. Such bonds shall be payable solely from the revenues derived from such municipally-owned utility or facility and such bonds shall not, in any event, constitute an indebtedness of the municipality within the meaning of any constitutional or statutory limitation, and it shall be plainly stated on the face of each bond that it does not constitute an indebtedness of the municipality within the meaning of any constitutional or statutory provision or limitation.
     The validity of any refunding revenue bonds shall remain unimpaired, although one or more of the officials executing the same shall cease to be such officer or officers before delivery thereof, and such bonds shall have all the qualities of negotiable instruments under the Law Merchant and Article 3 of the Uniform Commercial Code.