Select Roof Type


Stiffening Options



Self-Supporting Umbrella Roof No IFR

Self-Supporting Umbrella / Dome

The dome roof is formed with a spherical surface supported at its periphery. Under API standards, the unstiffened dome is typically used for tanks with smaller diameters.

API 620 Tanks Self Supported Dome Roofs


  • The bulk of the roof work can take place at grade

Self Supported Dome Roof



Self-Supporting Umbrella Roof No IFR Externally Stiffened

Self-Supporting Dome (Structurally Supported Grid Roof)

Stiffened domes are typically found on large diameter tanks that have internal pressures. The dome roof is formed with a spherical surface supported at its periphery.  Our custom designed grid roofs are built over a suspended deck at grade level and then raised to position.

TIW Designed Dome Grid Roof


  • The roof can be constructed safely at grade
  • Supports up to 15 PSI of internal pressure

TIW Designed Dome Grid Roof


Stiffening Options



Self-Supporting Cone Roof 650 NO IFR

Self-Supporting Cone

Suitable for small diameter tanks.

Stainless Cone Roof


  • Roof can be sealed
  • Supports up to 15 PSI of internal pressure



Self-Supporting Cone Roof 650 NO IFR Externally Stiffened

Self-Supporting Cone (Externally Stiffened)

Suitable for larger diameter tanks.  External stiffening can provide additional support for platforms and structures on the roof.

Stiffened Cone Roof


  • External Stiffening allows for a large diameter roof design
  • Roof can be sealed
  • Supports up to 15 PSI of internal pressure
  • Stiffening allows the tank roof to be designed to support heavy structures

Stiffened Cone Roof

Design Specifics

With over a century in tank design & field erection, we’ve continually developed and critiqued our design and construction process, producing a safer and longer lasting tank. Some design specifics considered include:


  • Allowable external Loads on tank shell openings
  • Internal & external Pressures
  • Environmental loads (wind, seismic, snow, importance factors)
  • Single or double bottoms
  • Flat, cone or dome bottoms
  • Foundation design
  • Design based on tanks operating at lower temperatures
    • Low Temp: Typically designed to API 620, Annex R, for storing refrigerated products as low as -60 °F (-51°C)
    • Cryogenic: Typically designed to API 620, Annex Q storing Cryogenic liquefied gases at temperatures not lower than –325 °F (-198.3°C)

Heat Conservation

  • Various insulation products


  • Product conditions
  • Maximum capacity
  • Secondary containment
  • Internal or external floating roofs

Materials of Construction

  • Carbon steel, stainless steel, duplex steel or high nickle steel

Corrosion Protection

  • Linings, coatings, wallpapering
  • Cathodic protection

Access Systems

  • Radial or spiral stairways
  • Roof access systems

API 620 Standard

The American Petroleum Industry (API) has established specific standards best suited for the design, fabrication and construction of low temperature and cryogenic storage tanks. TIW designs tanks to both API 650 and 620, each having its best fit depending on the unique requirements of the product being stored.


  • API 620 Standard


    The API 620 Standard governs the design and construction of large, welded, low-pressure storage tanks. These tanks require an elevated, flat or cone bottom, and a minimum material thickness of 3/16 of an inch in carbon steel, austenitic stainless steel and nickel alloys (low temperature only). These tanks operate as low as -325°F to 250°F with an operating pressure of up to 15 PSI. They are generally utilized for cryogenic liquefies such as LOX, LIN or LNG as well as other chemicals which require internal design pressures exceeding those allowed by 650 tanks.

  • API 650 Standard


    The American Petroleum Industry (API) has established the 650 standard, setting minimum requirements for the design, material, construction, and testing of aboveground, open and closed-top, cylindrical welded steel storage tanks of various capacities and sizes.

    They are designed as non-refrigerated tanks with a minimum material thickness of 3/16 inch of carbon steel, austenitic duplex stainless steel, and aluminium. Supporting an internal pressure of 2 ½ PSI or less and an operating temperature of -40°F to 500°F. They are commonly used to store products such as crude oil, petroleum by-products, chemicals and process water.

    Repairs, Modifications & Testing

    The API 650 Standard provides details for the minimum testing to be performed to ensure quality workmanship of the tank along with a separate standard, API 653, dedicated to providing a complete set of procedures and tests, specifically for the repair of API 650 tanks.

    We are well-known for our expertise in performing repairs and modifications for a wide range of customers. Please see our API 653 Repair Services for more details.


    Goto API 650 Product Page: api-650-tanks-various-configurations

  • AWWA D-100 Standard


    The American Water Works Association has set these guidelines for the construction of welded carbon steel tanks for water storage. The American National Standards Institute has adopted them as best practices within the industry for designing and building tanks to be used in water systems where the internal pressure does not exceed atmospheric pressure.


Our design engineers can customize a wide ranges of appurtenances on the interior and exterior of your tank. At our in-house, 200,000 sq ft material processing plant, we fabricate everything from pontoons, nozzles, vents and piping to ladders, custom stairways and platforms.

Here are some typical components we design, fabricate and install on our API 620 tanks:

Internal Components

  • Heating Coils
  • Baffles
  • Piping Subsystems for Multi-Level Sampling
    • Overflow
    • Draw-off
    • Diffusers
    • Pumping

External Attachments

  • Nozzles (with flanges, elbows, couplings and more)
  • Ladders, Spiral and Radial Stairways:
    • Single and Double Stringer Designs with Handrail Variations
  • Roof Walkways, Platforms and Joining Catwalks
  • Shell Manways and Mixer Manways
  • Rectangular and Circular Hatches
  • Insulation Rings
  • Lightning Arrestors
  • Rescue Davits
  • Piping Supports
  • Grounding Lugs

Managed Services

Protective Coatings & Insulation

With low temperatures, a diversity of the stored products and their chemical properties, and surrounding atmospheric conditions, there are a wide variety of internal and external protective coatings we can provide to prolong the life of the tank.

We also offer alternate corrosion options such as hot dip galvanizing, coating over galvanized components and fireproofing.

Shop Pre-Coating

TIW can shop coat floor plates, shell plates and appurtenances prior to shipping to site.  This can help offset the high prices of field coating and help minimize open-air blasting which can be environmentally prohibited in some project locations.


We provide galvanizing of various tank components – from nozzles, piping and support clips to stairways, handrails and platforms. In some cases, both galvanizing and coating are applied providing a superior protection.

Interior Linings

TIW removes all sharp edges before sandblasting any area, and can perform complete Holiday testing (to [1] test for voids in the liner), prior to signing off on the lining. Typical linings used include:

  • Epoxy primers
  • Epoxy finish coatings
  • Holding primers
  • High temperature coatings
API 620 APP Q Double Wall LOX Tank

Exterior Coatings

These coatings are applied to the exterior of tanks or vessels for corrosion protection and cosmetic appearance. Some typical coatings we use include:

  • High-performance epoxy primers and finish coatings
  • Inorganic zinc coatings
  • Holding primers
  • Acrylic polyurethane coatings
  • High-temperature coatings

To achieve the right conditions for low temperature and cryogenic storage varying types of shell, insulation and secondary containment systems are typically used.


Construction of a Cryogenic, double walled, LOX tank. 48’9″x44’3″ (Outer), 42’9″x44’3″ (Inner),  Designed to API 620, APP Q

API 620 Tank Low Temp

Tank Insulation

Typically insulated with rigid polyurethane insulation foamed-in-place between the steel shell and aluminum jacket, which prevents moisture vapor from entering and protects against weather.

TIW can supply and install a variety of mechanical insulation to meet the customer’s requirements.

Secondary Containment, Third Shell Course

Secondary Containment

The secondary containment wall (Outer Tank) provides additional insulation along with an essential line of defense in the event of a failure of the primary containment (Inner Tank). Providing the best possible insulation; contents are contained should a tank leakage occur (unlikely).


Construction of a secondary containment wall on a 160′ x 52′  API 620 tank, used for storing anhydrous ammonia.