Ovivo® Steel Digester Covers

Ovivo provides a wide variety of steel digester covers: Fixed, Gasholder, Hydroseal or Buoyant. Our digester steel covers are radial beam designed to be erected quickly and efficiently on site and offer a rugged structural design. A thrust ring is installed at the periphery of each cover to absorb all loads without transmitting excessive forces to the concrete digester wall.
  • Biogas and odor containmentSteel cover fill in photo_sm
  • Low acquisition and installation cost
  • Long, trouble-free life
  • Variable sludge storage capabilities
  • Easy operation and maintenance

The steel covers are an affordable and durable option for anaerobic digesters and/or biogas containment. These are available for tank diameters of different ranges and custom engineered to meet the customer’s requirements and needs, based on a wide variety of industry standards and proven design.

  • Simple, rugged structural design
  • Prefabricated roof sections available, for an easy and faster field installation
  • Easy to insulate, using commonly available roofing materials
  • No moving parts for simplified maintenance

The use of radial beams, and prefabricated roof sections for most of Ovivo’s projects allow for easier and faster field installation. During erection, covers are usually supported by radial beams attached to a center ring and the thrust ring, which add strength to the complete unit.

Ovivo’s cover design is compatible with all mixing systems to ensure an adequate anaerobic digestion process.







Trust Ovivo and our experienced staff. Leverage our track record for your digester cover applications. Our installation list counts more than 1,000 projects in North America alone, with sizes up to 125 feet in diameter!

Ovivo’s radial beam design can be supplied for the following configuration: Fixed, Gasholder, HydroSeal® type and Buoyant. Ovivo will provide the best option for each application based on our customer’s needs.

Ovivo® Fixed Steel Cover (Type F)
The Ovivo Type F fixed steel cover is the most economical cover available. The most common application is on digesters with constant water level (primary or first stage digesters). Fixed covers can be sealed against the tank to combat odors.

Ovivo® Gasholder (Type GV)
The Ovivo Type GV cover uses a radial beam design structure with added side sheets and ballasts for digester gas storage or flotation. Submerged ballast blocks are typically used to maximize cover stability and maintain adequate gas pressure. The design includes a vertical guide arrangement with tracks attached to the tank wall. Guide devices, spanning from the top to the bottom of the cover side sheet, are engaged to stabilize the cover.

HydroSeal® Steel Cover (Type GVL)
The use of a separate launder and liquid seal between the digester tank and the cover in the HydroSeal steel cover design eliminate gas, odor and VOC emissions and significantly improve service/maintenance access. As no components come in contact with sludge, corrosion issues are significantly limited and the equipment features an increased life expectancy and a trouble-free operation.


Ovivo® Buoyant Steel Cover (Type B)
The Ovivo Type B covers use radial beam design structure, including a peripheral buoyant chamber. The cover floats directly on the digester content. Precast concrete ballast blocks are provided to maintain a specified gas pressure. A major portion of the buoyant volume which keeps the cover afloat is located at the cover periphery; this feature provides an excellent resistance to tipping. A slide guide system will provide vertical movement preventing rotation or binding.

The EZ-RECT™ cover erection system is a feature that is available with most digester covers. Ovivo will provide the digester cover with cover plate/radial beam sections, pre-assembled and pre-welded, to facilitate the overall assembly and erection of the cover on site. Each assembly typically consists of two (2) beams and one (1) cover plate.

Ovivo offers this option to reduce the amount of field welding required to erect a cover of significant diameter. This will reduce the total amount of field welding for the digester steel cover. Furthermore, this will reduce the number of pieces to be handled during erection.

Cover erection is completed in five steps:

  1. Side Sheet Assmbly
  2. Center Ring and Erection Beam Installation
  3. EZ-Rect Cover Plate Assembly Installation
  4. Remaining Cover Plate Installation
  5. Manholes, Spools, Tubes, Etc., Installation

Q: Does the radial beam design require ballast?

A: Only the gasholder/floating (Type GV) cover requires ballast. The ballast regulates the pressure / weight of the cover. For the Fixed cover (Type F), everything is bolted down and the pressure is determined by the hold down strength of the anchors and the cover design values.

Q: Are the ballasts provided by Ovivo®

A: Ovivo provides the ballast calculations as part of the submittals. The ballast blocks are not provided by Ovivo and are typically provided by the contractors.

Q: What are the most common methods to install the ballast?

A: For installing the ballast blocks, these are the most common methods: 1) The cover can be built in place and the blocks installed prior to setting the loose cover plate panels. 2) The blocks are put in the tank and rest on the floor prior to lifting the cover in place. Slits are made in the cover and are used to lift the blocks in place. Slits are then welded. 3) The EZ-Ballast design offered by Ovivo, allows for approximately 3 ft of the plates sections to be kept ‘loose’ and welded after installation.

Q: What is the recommended maintenance on a steel digester cover?

A: Typically, every 10 years, a digester should be taken out of service for inspection of the beams/shell (for the presence of corrosion inside and outside of the digester). Ovivo recommends that covers be sandblasted and repainted at least every 10 years. For the vertical guide system, periodically inspection of the cover for proper travel of guides and wear of guide pads is required, to ensure a proper operation.

Q: How we can determine the side sheet length for Fixed Covers?

A: The side sheet should be extended below the minimum liquid level. Otherwise, two options are recommended:  1) The supplier of the filler material should confirm that it can withstand the operating pressure. 2) An independent clean liquid launder should be provided that allows for a pressure seal at any given sludge level (Contact Ovivo for additional details for this option).

Q: Would you normally blast and paint the segments at the fabricator or on site?

A: Handling of the equipment from the shop floor to the site can affect the surface of the cover. As such, Ovivo usually ships the steel covers unpainted, bare steel and sand blasted. Coating is performed on site, in the field.

Q: What is the benefit of the Smooth Underside (SUD) design?

A: With the SUD configuration, the underside is completely smooth and will have a better painting surface and less places for undesirable material to collect. Also, the radial beams over the plates create segments allowing application of insulation by sections.

Q: Are steel digester covers the only option available for gas containment?

A: No, Ovivo also supplies membrane gasholders, that uses a flexible material and provide a better control and flexibility of gas storage. Please see our Ultrastore™ membrane gasholder product, on our website.

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