Control Valve – NACE MR0175

NACE MR0175 – The National Association of Corrosion Engineers (NACE) has issued Standard MR0175 that specifies proper materials, heat-treating conditions, and strength levels that are required to provide good service life in sour gas and oil environments. NACE Standard MR0175 also provides material recommendations and guidelines for specific components including bolting and springs.

Figure 21 lists some of the NACE approved materials, hardness information, and pertinent remarks. Note that the maximum hardness that is allowed under the NACE guidelines depends on the material type.

Figure 21 shows, under the heading Remarks/Applications, that there are two NACE classes for bolting materials. Class III bolting allows more-or-less standard bolting materials (B7) provided the bolting is exposed to atmosphere. Class II bolting must be specified whenever the bolting will be in direct contact with a sour environment; i.e., if the valve is insulated or buried.

NACE MR0175 does not address elastomer and polymer materials. However, the importance of these materials for critical sealing must be considered. User experience has shown that nitrile, neoprene, and PTFE can be applied within their normal respective temperature ranges.

Some valve manufacturers have established standard policies and practices that ensure compliance with NACE guidelines whenever a valve is specified for sour service. For example, the following summarizes the procedures that are followed by Fisher Controls.
• Carbon steel bodies and bonnets are heat treated to 22 HRC maximum, and they are post-weld heat-treated.
• Martensitic and cast precipitation hardened stainless steels are not used.
• Control valve packing sets are jam style only (springless or externally live-loaded).
• Valve stems are made from Nitronic 50 when strength is required.
• Primary trim materials are S31600 and Alloy 6.
• No machining operations that cause work hardening of the materials are performed in the manufacturing process.
• Platings and coatings are applied over NACE approved base metals, and the coatings are not intended to provide corrosion protection.
• Bolting in Class III material is standard when the bolting is exposed to atmosphere. Bolting in Class II material is available when bolting is buried, insulated, or otherwise exposed to H2S.

Most valve manufacturers offer specific construction options that comply with the NACE guidelines. Refer to Table 7 in Bulletin 51.1:ES (Fisher Catalog 71) and note the standard trim options that are NACE approved.

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