When the medium contains hydrogen sulfide and carbon dioxide, standard valves face a serious threat: sulfide stress cracking can cause sudden, catastrophic failure. For these aggressive environments, the HH-grade safety valve represents the highest level of material protection available.The main safety valve product names of China safety valve Network include:Quick Switching Safety Valve,Spring Low Lift Safety Valve,Spring Low Lift High Pressure Safety Valve,Spring Low Lift Closed High Pressure Safety Valve,Spring Fall Lift Closed High Pressure Safety Valve,Spring Fall Lift Safety Valve,Spring Fall Lift Safety Valve With Radiator,Spring Low Lift Air Compressor Safety Valve(With Connecting Pipe),Safety Reflux Valve,Single Lever Safety Valve,Spring Fall Lift, Low Lift Thread Safety Valve,Sleeve Insulation Safety Valve.

What HH Grade Means for Safety Valves

HH is a material class defined by API Specification 6A. It requires corrosion-resistant alloys on all fluid-wetted surfaces. This is the most stringent material requirement for wellhead and surface equipment. HH-grade valves are designed for high-pressure, high-H2S environments where standard carbon steel or low-alloy steel would fail rapidly.

Why Sour Gas Demands Specialized Materials

Sour gas contains H2S, which dissolves in water to form a weak acid. This promotes hydrogen absorption into steel, leading to sulfide stress cracking. The problem worsens with higher H2S partial pressure, chloride concentration, and temperature. Materials must be selected according to NACE MR0175/ISO 15156. This standard sets hardness limits, chemistry requirements, and qualification procedures for metallic materials in H2S service.

Key Materials Used in HH-Grade Valves

HH-grade safety valves typically use super nickel-based alloys for wetted parts. These include Hastelloy C276 and C22, Inconel 625 and 718, and Monel. Hardfacing is applied to seating surfaces using Stellite or similar alloys. Springs are often made from Inconel X-750, which resists both corrosion and relaxation at elevated temperatures. The valve body may be carbon steel or low-alloy steel with full wetted-surface overlay, or solid corrosion-resistant alloy.

Manufacturers with HH-Grade Capabilities

Several manufacturers offer safety valves suitable for HH-grade sour service.

Farris Engineering (Curtiss-Wright) provides spring-loaded and pilot-operated relief valves with materials including Monel, Hastelloy C, Duplex, and NACE-compliant options. Their product range covers API 526 dimensions and is widely used in refining, petrochemical, and natural gas production.

Emerson (Anderson Greenwood, Crosby) offers direct spring-operated and pilot-operated safety valves with NACE-compliant trim options. The Crosby J series is available with materials conforming to NACE MR0175/ISO 15156.

LESER manufactures safety valves with special alloy options including Duplex, Super Duplex, Monel, Hastelloy, Inconel, and Titanium. Their NACE level concept allows efficient material selection for different sour service conditions.

Chinese Manufacturers including Shanghai Shenkai and North China Rongsheng have developed HH-grade wellhead equipment and safety valves. Shenkai offers HH-grade wellhead assemblies rated up to 20,000 psi with super nickel-based alloy overlay technology.

Selection Guidelines

When specifying an HH-grade safety valve, provide the manufacturer with H2S partial pressure, chloride concentration, temperature, and pressure rating. Request material certifications per NACE MR0175/ISO 15156 and API 6A. Verify that all wetted components meet HH material class requirements. For critical applications, require PR2 performance testing and fugitive emission certification.Do you still need to know or purchase the following safety valve products:

• Air Compressor Safety Valve
• A69Y Main Safety Valve(W Series) Welding Safety Valve
• Anti-sulfur Spring Type Safety Valve
• ANSI Bellows Safety Valve