Choosing Between API 620 and 650 for Your Storage Tank

May 27 2016

bigstock-Oil-Refinery-Tanks-2037186.jpgThe American Petroleum Industry (API) has established standards for the design, fabrication, and construction of welded steel storage tanks for storing oil. The most popular tanks available on the market today are the 620 and 650 models, but which is right for you?

The answer depends on what you require out of the product.API 620 regulates the design and manufacture of large steel low-pressure storage tanks, usually larger than 300 feet in diameter.  By contrast, API Standard 650 is typically used for carbon, stainless steel and aluminum tanks located in terminals, refineries, pipelines and other process facilities. Both have different pressure and temperature parameters as well.  Your choice of model will depend on you and/or your client’s particular needs.

Actual Standards

If you require the complete API Standard 620, 10th Edition, February 2002, click here.  For the complete API Standard 650, 10th Edition, March 2007, click here. 

API 620

The design configuration of API 620 requires that you have an elevated or flat bottom on which to store it. The tank has a single, vertical, central axis of revolution with a minimum material thickness of 3/16 inches.  Other attributes of API 620 include:

  • It is constructed from carbon steel, austenitic stainless steel, and nickel alloys (low temperature only).
  • A Welding Certification is stipulated by the American Society of Mechanical Engineers (ASME), Section 10.
  • There is a required inspection, no third party.
  • The inspection cost is the cost of the non-destructive inspection (NDE)

Benefits of API 620 are:

  1. It is used for products that have high internal pressure such as liquefied natural gas (LNG) and cryogenic tanks.
  2. It can store contents at a higher pressure (maximum 15 pounds per square inch (PSI) of gas or vapor storage) and lower temperature (-325 degrees F to 250 degrees F) than API 650.
  3. It can store any liquid.

API 650

bigstock-Storage-Tanks-For-Petroleum-Pr-116066573.jpgAPI 650 sets minimum requirements for the design, material, construction, and testing for aboveground, open and closed-top, cylindrical steel storage tanks in different capacities and sizes, roughly equating to the pressure of the atmosphere (not greater than the weight of the roof plates).  If additional requirements are met, higher internal pressures are allowed.  API 650 only covers tanks that support the whole bottom evenly and tanks in non-refrigerated service that have a maximum design temperature of 200 degrees F.  It requires that you have a minimum material thickness of 3/16 inch.  Other attributes of API 650 are:

  • It is constructed from carbon steel, austenitic duplex stainless steel, and aluminum
  • A Welding Certification is stipulated by the American Society of Mechanical Engineers (ASME), Section 10.
  • There is a required inspection, no third party.
  • The inspection cost is the cost of the NDE.

Benefits of API 650 include:

  1. It can store oil, gas, chemical, water, and biofuel for some of the most common tanks in the oil industry.
  2. It can store contents at a lower pressure (maximum of 2 ½ PSI) but at a much higher temperature (-40 degrees F to 500 degrees F) than the standards of API 620.
  3. It can be any tank size.

Hopefully, this article provides some clarification for those of you in the metal fabrication industry regarding the key differences between API Standards 620 and 650 for storage tanks.  

To quickly summarize, API 620 can store contents at a lower temperature and higher pressure whereas API 650 permits a lower amount of pressure at a higher temperature.

Given that, and knowing your specific pressure and temperature requirements, you can see that choosing your standard carefully is critical. Contact steel fabricator in Toledo, Swanton Welding to help you with your steel storage tank fabrication.

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