Valve Magazine - Summer 2011

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 service.

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 tspence@flowserve.com.

; Difficulties in machining

; Expensive

; Difficult to weld repair in aged condition

; Critical sealing surfaces do not require overlay

; 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 produced fluids.

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.

MISCELLANEOUS
MATERIALS

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 jtibbs@vma.org. For questions about advertising, contact Sue Partyke, Advertising Director, at spartyke@vma.org.

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