Most onshore and offshore installations traditionally use ball valves and
occasionally gate valves for the majority
of flow isolation applications. Specifications typically call for 6D valves, but
engineers seldom look beyond these
specifications to other valve types with
similar or better performance.
Many of these engineers are not yet
aware that in many offshore isolation
applications, a triple offset valve (TOV)
offers benefits in terms of weight, overall dimensions and performance versus
the standard ball or gate valve. A TOV
can be the right choice for applications
in the turret of a floating production
storage and offloading vessel (FPSO),
and in virtually all topside process applications of FPSOs and platforms such as
separators, water treatment, gas compression and other systems.
Today’s TOVs, with pressure ratings
up to ASME Class 1500 and zero leakage, cover enough applications to achieve
significant savings in weight and space,
as well as total cost of ownership.
Allowable Leakage Rates Compared
API 598
Metal
Diameter Seated
Air
(*)
24
24
24
40
40
40
56
56
56
56
56
56
56
56
FCI 70-2
Class IV
MM INCH Liquid
API 6D
Metal
Seated
Air
(**)
14
18
27
36
45
54
63
72
81
90
108
135
162
189
Liquid
0.46
0.61
0.91
1. 21
1. 52
1.83
2. 14
2. 44
2.74
3.05
3.66
4. 57
5. 48
6. 40
API 598/
API 6D
Soft Seated
Liquid/Air
(*)(**)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Air
0.90
1.70
4.00
6.75
11. 10
16.00
21. 60
28. 40
-
-
-
-
-
-
HISTORY
The TOV design was introduced in the
early 1970s as the next great development after the high-performance butterfly valve. The design is totally different
from conventional or high-performance
butterfly valves, however, offering a 90-
degree non-rubbing rotation and metal-seated zero leakage.
Since the TOV was introduced, it has
become a success with end users in the
downstream oil and gas, process and
power industries. It is recognized as a reliable, robust and valid alternative to gate
and globe valves as well as ball valves.
The TOV concept is applied in a wide
variety of applications from cryogenic
to high temperature and from low- to
high-pressure where positive isolation is
required. Since its introduction, more
than 500,000 TOVs have been installed
worldwide with an extremely wide range
of sizes and ratings and different materials—from WCB to duplex and from
CF8M to titanium.
DESIGN
In the triple offset geometrical design of
TOV, the valve shaft is double offset
