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Speciale valvole industriali e manutenzione d’impianti

EmErsON

Emerson’s Vanessa Triple Offset Valves Offer an

Effective Top Entry Design to Ensure Safe Trim
Accessibility in LNG Cryogenic Applications

Specifying a port entry in buttweld valves in the nant. Furthermore, being a high quality torque
LNG industry has become extremely common seated, metal-to-metal non-rubbing TOV, the
in recent years in response to the need of end top-entry access of a Vanessa valve is specified
users to align with regulatory requirements such on clean cryogenic services for extraordinary
as EN 1473 or NFPA 59A and comply with local repairs, not for ordinary maintenance.
regulation, especially for LNG terminals. Spe-
cifying valves with fewer flange connections is Triple Offset Valves?
critical, and welding valve bodies to the pipe Significant technological developments have
appears to be an obvious solution. However, been made in the butterfly valve segment over
when a problem arises, operators must gain the past 40 years -- the reduction or complete
access to the key components for maintenance elimination of rubbing during rotation being part
and repair. of the evolution of this type of valve.
Emerson’s Vanessa cryogenic triple offset val- A TOV provides closing with no rubbing across
ves (TOVs) are commonly installed worldwide in the 90° rotation (differently from double offset
double flanged, lug, buttweld with double flan- valves) because of a single, instantaneous con-
ged being the most commonly adopted style. tact between sealing elements only when clo-
However, whenever inline access is required, a sed position is reached. Emerson’s Vanessa
buttweld top entry execution is now predomi- TOVs can handle bidirectional flow and tight in
both sealing directions up to extreme pressures
due to torque seating and non-rubbing rotation
achieved with three “offsets” (fig. 1):
Based on these premises, the seal ring (and
not the disc itself as in the case of concentric
butterfly valves) is the critical component as it
represents the key flexible element necessary to
perform sealing against a seat typically overlaid
with Stellite grade 21.
A cryogenic TOV is a valve with an extended
bonnet and a solid seal ring, available across
a wide range of body styles. The Vanessa seal
ring is always a one-piece solid ring in Nitronic®
50 (Solid Seal Ring), a material highly resistant
to corrosion able to preserve important mecha-
nical features at low temperatures.

Available Solutions for Cryogenic LNG Ap-
plications: Top Entry Buttweld Design
On clean liquid/gaseous cryogenic applica-
tions, Emerson’s Vanessa TOVs are virtually
maintenance free and do not require any spe-
cific maintenance programs. To do so, cryoge-
Figure 1: The TOV’s smart design offers longer lifecycles and improved nic TOVs must be able to guarantee the same
leakage performance, and requires lower maintenance for cryogenic ap- performance irrespective of body style designs.
plications. Typically, this is linked to the valve trim compo-

72 72 Impiantistica Italiana - Novembre-Dicembre 2017