API 650

ALPHA Tank adheres to the API-650 Specifications when building any tank. This tank Standard was developed by the American Petroleum Institute (API) for above-ground petroleum storage tanks (AST) but has become the internationally recognized standard for building most above-ground liquid storage tanks.

The Standard has gained international recognition and is the standard of choice of most builders of large liquid above ground storage tanks. One reason for this is that the API 650 Standard was created and is revised by API committees comprised of the world’s best tank structural engineers who also rely on the experience of tank owners and tank construction companies. Second, the Standard calls for calculations based on the specific gravity of the liquid product being stored. This permits the thickness of the steel needed as well as other specifications of how the tank is built to be determined by the weight of the product. Thus, the Standard has the built in flexibility to be used in building tanks to store a wide variety of products while ensuring the structural stability of the tank.

API 650 Standard Specifies Requirements for:

  • TYPE OF MATERIAL TO BE USED
  • CALCULATION USED FOR STEEL MATERIAL THICKNESS
  • NARROW RANGE OF TOLERANCES FOR PEAKING AND BANDING OF SHELL
  • WELD SPACING
  • THICKNESS FOR NOZZLE AND MAN-WAY REINFORCEMENT PADS
  • WELDER REQUIREMENTS AND TESTING CERTIFICATIONS
  • STRUCTURE VARIANCES BASED ON EARTHQUAKE OR HEAVY WIND CONDITIONS

 

 

Specifications for construction

  • Construction method: construction preparation→material inspection→cutting→machining→inspection→welding of the center plate at the bottom of tank→welding of the arch edge plate at the bottom of tank→setting up the center post and umbrella stand→installation and welding of top ring→installation and welding of edge and steel angle→assembling of temporary arch bracket→installation of leading chain lifting device→installation and welding of arch roof→installation and welding of the lower circle→Jack-up the top circle shell plate→welding of circular seam→installation and welding of every circular seam→installation and welding of bottom circle, bottom plate and angle seam→installation and welding of edge plate of bottom plate→inspection→installation of accessories→vacuum test→test→settlement observation→hand over.
  • Prefabrication: prepare sample plates, one sample plate for checking curvature of arch roof which the length is more than 2 meters, one inner arc sample plate for checking the deformation of the edge of vertical welded seam which the length is no less than 1 meter and one outer arc sample plate for checking the deformation of vertical welded seam which also the length is no less than 1 meter.
  • Assembly: before assembling the bottom plate, the lower surface  should be applied with anti-corrosion material.  A cross center line should be drawn on the surface of the bottom plate on the basis of acceptance. When the deviation of the center line remarked by civil construction is large, it should be adjusted to the minimum.
  • Welding and weld seam inspection: evaluate the welding process of butt joint, T fillet weld and tube plate, and to work out the guide book for welding process on site and the person who does the NDT for weld seam of storage tank. Radiographic inspection is done based on the specification and quality of butt joint welded by steel melt weld.

Inspection Methods

  • The tank body test: bottom plates vacuum box to test the leak of all bottom plates weld seam. (vacuum degree should be more than 53Kpa). For re-inspection, dye penetration test will be used.
  • Tank water filling test: to observe the foundation settlement according to the up and down test of floating disc. Close the holes of ground part temporarily and open the light hole of the tank roof and then fill the tank with water. The water for test should adopt fresh water and the temperature should be higher than 5 ℃. The pressure should be kept for 48 hours.
  • The leak test, strength test and stability test for wall and roof of storage tanks: to close the light hole of tank roof, foam holes and vent holes when the water level is higher than 1 meter, then to fill water continuously, and to observe the pressure through the pressure gage setting on the tank roof. After water filling test is the stability test. Close all the opening when the water reaches the maximum operation liquid level. And then drain the water slowly, meanwhile, monitor the negative pressure number strictly, stop drain water when the number of negative pressure reaches 200mm, and to fill water into the tank in order to make the pressure normal.
  • Crack detection: Perform dye penetration test or magnetic powder inspection for the fillet weld seam of joint and stiffening plate on the tank.