Butterfly Valves for Marine & Offshore

DNV GL Type Approval (per DNV Standard ST-0378 for Offshore and Marine Machinery Components) is a certification process where DNV GL's engineering experts review a manufacturer's product design, manufacturing procedures, quality control system, and test results, and issue a Type Approval Certificate (TAC) confirming the product meets DNV's requirements for marine and offshore use. Type approval is required by DNV GL for all valve types within their scope — including butterfly valves used on seawater, fuel oil, ballast, and fire-fighting systems — as a condition of classifying a ship under DNV rules. Without a valid TAC, the valves cannot be installed on a DNV-classed vessel without individual item approval (a much slower and more expensive process). The TAC covers specific valve models, sizes, pressure ratings, and materials — not a blanket approval for all products from a manufacturer. When ordering marine butterfly valves: specify the class society (DNV GL, Lloyd's Register, Bureau Veritas, ABS, NK, CCS), confirm the manufacturer's TAC covers your specific size, pressure class, and material, and request a copy of the TAC for your project records.

Rubber-lined (elastomer-seated, concentric) butterfly valves are the most widely used butterfly valve type in shipboard seawater cooling, ballast, and bilge service due to their low cost, proven performance, and class society approval availability. Key considerations for seawater service: (1) Liner material: EPDM is the standard for seawater cooling (excellent seawater resistance up to 100°C); Natural Rubber (NR) for bilge service; NBR for oily bilge water and fuel oil-contaminated service; (2) Body material: duplex 2205 or naval brass C83600 for direct seawater contact — standard SS 316 bodies can suffer crevice corrosion at flange bolt holes in continuous seawater immersion; (3) Disc material: duplex 2205 or SS 316 discs are standard — aluminium is used in HVAC duct butterfly valves but not in seawater; (4) Limitations: rubber-lined butterfly valves are not fire-safe — they must not be used on fuel oil service, cargo manifolds, or any location where a fire hazard exists. For fire-safe service (fuel oil, cargo), use triple-offset metal-seated butterfly valves.

The IMO Ballast Water Management (BWM) Convention (International Convention for the Control and Management of Ships' Ballast Water and Sediments, 2004) entered into force in 2017. It requires all ships over 400 GT operating internationally to manage their ballast water using an approved Ballast Water Management System (BWMS) to prevent the spread of invasive aquatic species between ports. The BWM Convention affects butterfly valves in multiple ways: (1) BWTS installation requires new butterfly valves on the ballast water treatment bypass lines, filter inlet/outlet, and UV or electrochlorination treatment modules — all must comply with the BWMS Code (Circular BWM.2/Circ.67) type approval process; (2) Existing ballast main valves (sea chest to ballast tanks) used with the BWTS must be compatible with the biocides used — hypochlorite electrochlorination treatment generates Cl₂ which attacks elastomers; EPDM is the standard liner for chlorine-treated ballast water (not NBR or natural rubber); (3) Duplex stainless steel butterfly valves are increasingly specified for BWTS applications due to chlorine resistance. Valves supplied for BWTS must be specifically listed in the BWTS manufacturer's IMO type approval documentation.