Dafram Special Applications Ball Valves
Subsea valves are designed according to API 6DSS to withstand external pressure corresponding to 3000 meters water depth. Special features are employed and different layout (fully welded body, split body, top-entry, soft/metal seats, triple barrier stem sealing etc). Valves can be hyperbarically tested according to Customer specifications. PR2 test certifications are available.
If solid particles are contained in the fluid, valves are provided with Tungsten Carbide (WC) coated metal ball and seats to avoid the erosion of the sealing surfaces.
HIGH TEMPERATURE SERVICE
Some processes require valves able to be operated and to assure leakage rates within specified limits at high temperatures. In these cases Dafram provides a special valve design including extended bonnet (recommended for use at temperatures over 250°C), gaskets and seals and material selection suitable for high temperature service. For application where soft seats would be unsuitable, Tungsten Carbide (WC) or Chromium Carbide (CrC) coated metal ball and seats are used.
HIGH PRESSURE SERVICE
Trunnion ball valves can be properly designed for very high pressure ratings such as per API6A 2000 to 20000 and ASME B16.34 4500 classes. Dafram can perform internally special tests as per API 6A requirements.
Some gas treatment processes require valves able to be operated and to assure leakage rates within specified limits at low temperatures. In this case Dafram provides a special valve design including extended bonnet (recommended for use at temperatures below minus 50°C), gaskets and seals and material selection suitable for cryogenic service.
SOUR SERVICE (API 6D, 7.7)
Materials for pressure-containing parts of valves used in H2S-containing environments in oil and gas production shall meet the requirements of ISO 15156 (NACE). HIC and SSCC corrosion test certificates can be provided on request.
High Alloys, Nickel Alloys, Duplex (22Cr – 2 Ni) and Superduplex (25 Cr – 5 Ni) can be supplied according to corrosion resistance requirements as per special material standards (i.e. Norsok MDS D46 and D44 for Duplex, D56 and D54 for Superduplex, or similar standards). In addition Electroless Nickel Plating (ENP) and 316L SS or Alloy 625 weld overlay are frequently used to enhance corrosion resistance of balls, seats, stems, seat pockets and stem sealing areas, in corrosive service.
EMISSION FREE VALVES
Ball valves are often required as “emission free valves” that is able to comply with the updated regulations which state very low rates of emission from the valve to the atmosphere. In this case special valve design including high body and stem surface finishing and suitable seals is available.
Anti explosive decompression O-rings or Lip seals are used to eliminate the possibility of O-ring explosion due to the sudden decompression of gas absorbed by the molecular structure of elastomeric sealing elements.
PARTICULAR FLUIDS Carbon Dioxide, Chlorine, Oxygen
Valves working with particular fluids, must meet some special requirements according to Dafram special procedures. To avoid risk of explosive decompression in Carbon Dioxide (CO2) service special O-rings or Lip-seals are used. Valves to be used with Chlorine need special features and a full degreasing and decontamination. Valves for Oxygen service requires also special features to eliminate the risk of ignition.
SPECIAL VALVE PATTERN
On customer request Dafram is able to design and manufacture special valve pattern such as three & four-way trunnion mounted ball valves or valves incorporating different special design features.