UL 142, API 12F What is it you are wanting to know?
BABRT's

The difference between API 650 and API 12F, mentioned by dkhunna is the size.
API 650 applies to large, field erected tanks, whereas API 12F applies to smaller, shop fabricated tanks.
I don't have the standards on hand at this moment, so I can't tell you up to what size goes 12F and at what size 650 starts. You'll have to check.
There's also API 620 that applies to low pressure storage tanks (up to 10 psig), used for highly volatile liquids, i.e., liquids that have a high vapor pressure, and for this reason they have a dome roof.  Appendix R of API 620 applies to cryogenics tanks, i.e., those working at very low temperatures.
There's also AWWA D100, developed for water storage at atmospheric pressure. Actually, it's used also for non-flammable liquids. AWWA is the American Water Works Association.
Giovanni S. Crisi
Sao Paulo - Brazil