eCFR Subpart K 
[ecfr.gov]
This subpart applies to:
- Petroleum liquids storage vessels with a capacity of more than 40,000 gallons (151,412 liters) that commence construction or modification:
- Commences construction or modification after March 8, 1974 and prior to May 19, 1978 (If > 40,000 and ≤ 65,000 gallons)
- After June 11, 1973 and before May 19, 1978 (If > 65,000 gallons)
Storage vessels constructed, reconstructed or modified after May 19, 1978 or July 23, 1984 are subject to NSPS Ka or Kb, respectively.
Not subject to this subpart:
- Storage vessels used for petroleum or condensate stored, processed, and/or treated at a drilling and production facility prior to custody transfer.
Important Distinction:
Petroleum liquids means petroleum, condensate, and any finished or intermediate products manufactured in a petroleum refinery but does not mean #'s 2 through 6 fuel oils as specified in ASTM D396-78, 89, 90, 92, 96, or 98, gas turvine fuel oils #'s 2-GT through 4-GT as specified in ASTM D2880-78 or 96, or diesel fuel oils #'s 2-D and 4-D as specified in ASTM D975-78, 96, or 98a.