The design, fabrication, erection, inspection and testing of above ground atmospheric storage tanks fabricated of carbon steel and austenitic stainless steel should be in accordance with API STD 650.
Tanks within the scope of API STD 650 Appendix A or Appendix J may be entirely designed, fabricated, erected, and inspected per API STD 650 except:
- All horizontal shell joints shall be complete penetration and complete fusion welds
- Pneumatic testing per API STD 650 Appendix J should be submitted to the requisition engineer for approval prior to execution
- The gap between the bottom shell ring and the lap bottom plates at the radial weld location should be a maximum of 1/8"
For tanks with shell thickness greater than 1/2" and temperature less than 32°F, the lowest two shell courses and annular plates should be constructed from fully killed carbon steels manufactured to fine grain practice and normalized or quenched and tempered.
The minimum corrosion allowance of 1/16" should be provided on carbon steel shells and bottom.
Carbon steel bolts for flanged connections should conform to ASTM A 193A 193M, Grade B as a minimum. Bolts shall consist of regular unfinished machine bolts with one heavy semi-finished hex nut. ASTM A 307, Grade B may be used for structure purposes only.
For heated tanks (160°F or higher), a bottom rainshield should be installed.