API 620 For Large Field-Erected Storage Tanks

API 620 is a key engineering standard for the design and construction of large, welded, low-pressure storage tanks assembled at their final site. It is relevant to petroleum products, chemicals, water-treatment facilities, liquefied products and other materials that require substantial atmospheric or low-pressure containment.

The standard addresses engineering principles, materials, fabrication, welding, inspection and testing. It helps project teams establish a consistent technical basis before tank plates, roofs, shells, nozzles and foundation interfaces are manufactured or erected.

For Australian projects, the document may support work at a Pilbara mine, a Gladstone processing facility, a Kwinana terminal or a coastal fuel installation. It should be read alongside the project specification, Australian legislation, environmental approvals and applicable AS/NZS requirements.

A downloadable PDF is useful when engineers, inspectors and procurement staff need immediate access during design reviews or site work. Document Bays provides digital copies of technical standards for purchase, with major payment methods and multiple currencies available to support local and international project teams.

Standard or reference	Typical application	Main distinction
API 620	Large welded, low-pressure storage tanks	Covers tank design, construction, examination and testing
API 650	Large welded atmospheric storage tanks	Commonly used for atmospheric-pressure petroleum and liquid storage
API 653	Existing aboveground storage tanks	Focuses on inspection, repair, alteration and reconstruction
AS 1940	Flammable and combustible liquids in Australia	Provides Australian storage and safety requirements
AS/NZS 3500 series	Plumbing and drainage installations	Relevant to connected services, not tank structural design

What The Standard Covers

The document establishes requirements for tank geometry, shell and roof design, allowable stresses, stability, openings and appurtenances. It also deals with loads such as internal pressure, vacuum, wind, seismic effects, snow where applicable, operating loads and construction conditions.

A large field-erected tank is affected by more than its nominal capacity. Settlement, shell course tolerances, roof loads, thermal movement, product density and nozzle forces can all influence the final design. API 620 gives the engineering team a common framework for evaluating these issues.

The purchaser’s specification remains important. It may define the stored product, operating temperature, corrosion allowance, design life, lining system, inspection category and supplementary requirements. The selected edition should be checked against the contract and regulator expectations before procurement begins.

Choosing The Right Storage Standard

API 620 is generally associated with low-pressure tanks that need a more specialised design basis than conventional atmospheric storage. API 650 may be the better reference for many standard aboveground petroleum tanks, while API 653 is intended for assessing tanks already in service.

The distinction matters during early project definition. Selecting a document because a tank is simply “large” can produce gaps in pressure design, materials selection or inspection planning. The tank’s pressure range, temperature, product characteristics and construction method should guide the decision.

Australian facilities may also need to consider AS 1940, dangerous-goods rules, state or territory environmental conditions and requirements from bodies such as WHS regulators. These references do not replace the tank design standard; they add local obligations around separation distances, fire protection, containment and safe operation.

Design Inputs And Engineering Review

Before calculations begin, the project team should establish design pressure and vacuum, maximum and minimum operating temperatures, liquid specific gravity, fill level, corrosion allowance and expected cycling. Wind conditions are particularly significant for exposed sites, including remote Western Australian operations and cyclone-prone northern regions.

Foundation design deserves early coordination. Differential settlement can affect shell stress, roof support and connected piping. Civil, mechanical, electrical and instrumentation disciplines should agree on anchor arrangements, earthing, access platforms, ladders, drains, vents and emergency systems before fabrication drawings are released.

Materials must suit both the stored medium and the service temperature. Welding procedures, consumables, impact-testing requirements and heat treatment may be controlled by the standard, the material specification or the purchaser’s additional conditions. A competent engineer should confirm the complete design basis rather than relying on an isolated calculation.

Fabrication, Welding And Inspection

Field erection requires disciplined control of shell alignment, plate fit-up, weld sequencing and dimensional tolerances. Large tanks are often assembled in demanding environments, where wind, heat, dust and long supply routes can affect productivity. On a site outside Newman or near a remote gas operation, inspection planning needs to account for access and specialist availability.

The standard’s examination provisions should be converted into an inspection and test plan. This may include visual inspection, radiography, ultrasonic examination, liquid penetrant or magnetic particle testing, hydrostatic testing and leak checks, depending on the tank design and contract requirements.

Quality records should be retained throughout the work. Material certificates, welder qualifications, welding procedure records, non-destructive examination reports, repair logs and test results provide evidence that the completed vessel meets its approved design. Clear document control is especially valuable when the owner, EPC contractor and tank fabricator operate across different countries.

Practical Checks Before Purchase

A digital standard is most useful when the project team confirms its scope before ordering. The following checks help prevent a mismatch between the purchased document and the tank being designed:

• Confirm the required API 620 edition with the client and contract.
• Identify whether the tank is atmospheric, low-pressure or vacuum-sensitive.
• Check the product, density, temperature range and corrosion risks.
• Review Australian state or territory dangerous-goods requirements.
• Confirm related standards for welding, materials, coatings and inspection.
• Establish whether the PDF must be accessible to inspectors and subcontractors.
• Keep the purchased document under controlled revision management.

It is also sensible to compare the standard with the project’s design deliverables. If the specification calls for seismic assessment, fireproofing, internal floating equipment or specialised insulation, those requirements may need separate engineering references and approvals.

Teams researching connected technical subjects can also use an engineering reference resource during early information gathering. Any external material should be treated as supplementary, with contractual and compliance decisions based on the applicable standard and authorised project documents.

Accessing The Standard For Project Use

Purchasing a legitimate PDF gives engineers and inspectors a practical reference for design meetings, tender reviews and construction surveillance. It can be stored within a controlled project library and accessed by teams working between an office in Perth, a fabrication yard in Malaysia and a tank site in Queensland.

Before downloading, verify the title, edition, format and permitted use. Standards are frequently updated, and an older copy may not satisfy a client’s specification. Procurement teams should also confirm whether separate documents are needed for inspection, welding qualifications, materials or in-service assessment.

For cost-conscious purchasing, project teams can review standards price reductions when available. Once the correct edition is secured, engineers can apply its requirements alongside Australian regulations, approved drawings and the project inspection plan to support a safer, more traceable tank build.

Use the applicable API 620 PDF as a controlled engineering reference from design through field erection, and place the verified standard at the centre of your project documentation and compliance process.