tanks that are welded in the field and
cannot easily be post-weld heat treated. However, it is practical and sometimes required by ASTM specifications such as A744 to post-weld heat
treated castings. Therefore, if the
higher carbon CF8 and CF8M alloys
are post-weld, heat treated, they can
be used and will not experience intergranular corrosion in a nitric acid
Because of all of this, the choice
between these CF8 and CF8M for
nitric acid service should be based on
price and availability. VM
THOMAS SPENCE is director of materials
engineering for Flowserve Corp.
( www.flowserve.com), Dayton, OH. Reach
him at email@example.com.
; Difficulties in machining
; Difficult to weld repair in aged
; Critical sealing surfaces do not
; Nickel is subject to content limits
in NACE specifications, though
this applies only to low alloy steels.
Each of these alloys has successfully
been used for subsea valves, and all have
some type of environmental limitation.
For subsea valves, three options have
been standardized to handle all conditions. This is based on the three environments mentioned initially (H2S, CO2 and
chlorides). Options are as follows:
1. Alloy steel with selective cladding
on all sealing surfaces using a
CRA material such as Alloy 625.
This option will handle H2S with
low CO2. Cladding is used on surfaces to minimize pitting in critical sealing locations from chlorides that may be present in
2. Stainless steel with selective
Figure 4. Alloy bodies with cladding on all process wetted surfaces
Coming in Valve Magazine this fall...
cladding on all sealing surfaces
using a CRA material. This option
will handle CO2 with limited H2S,
for pitting resistance with chlorides that may be present in produced fluids.
3. Alloy bodies with cladding on all
process wetted surfaces (Figure
4). This option will handle the
most severe environments encountered during production. Although
this option is the most expensive,
it is the most versatile and can be
used for water injection in the
future to enhance production.
In addition to materials for the valve
bodies, special consideration must be
given to materials for miscellaneous
components or the “jewelry” that is necessary in subsea systems. These components include gates, seats, stems, gaskets
and fasteners. Materials for such components include stainless in the 3XX grades,
copper alloys, 6Mo and nickel-based
alloys such as UNS NO8825, S66286,
S21800, NO9925, NO7718, NO7750,
R30035, R30003 and titanium.
With miscellaneous materials where
; VMA’s Annual 2012 Market Outlook
; Where Valves Are Used: Power Generation
; Pipeline Valves
; Controlling Noise
; Coatings & Chemicals
; Actuators in Nuclear Applications
; And more!
To discuss editorial, contact Judy Tibbs, Editor in Chief, at firstname.lastname@example.org.
For questions about advertising, contact Sue Partyke, Advertising Director,
When you need exceptional quality and on-time delivery look to Nova Machined Products to
be there for you. Experience counts. For over 25 years we have been manufacturing precision
machined parts and assemblies to exact customer specifications. Our milling, turning, grinding and
assembly capabilities are designed to handle simple or complex, close tolerance requirements.
Whether it’s a long-term project or an emergency, we are here to service your needs, 24/7.
34 | Valve MAGAZINE
Summer 2011 | 41