The difference between API 6A Gate Valve and ordinary gate valve

1. Standards and Certifications
API 6A Gate Valves
Manufactured in accordance with the American Petroleum Institute's API 6A, Specification for Wellhead and Christmas Tree Equipment.
This standard is an internationally recognized standard for the oil and gas industry, covering the entire process, including materials, design, manufacturing, testing, inspection, and quality control.
API 6A, for high-pressure oil and gas wellheads, requires products to meet the following requirements:
PSL (Product Specification Level): From PSL1 to PSL4, the higher the level, the more stringent the requirements.
PR (Performance Requirements): Specifies performance indicators for pressure, temperature, sealing, and service life.
Temperature Class (T): Covers operating conditions from extremely cold to high temperatures, such as L, P, and X temperature ranges.
NACE MR0175/ISO 15156: Ensures safe operation in corrosive environments containing hydrogen sulfide (H₂S).
Common standards for standard gate valves include API 600/602/603, ASME B16.34, and GB/T 12234. This valve is primarily used in conventional industries such as municipal pipelines, boilers, power plants, chemicals, and ships.

Sulfide resistance and high-pressure resistance requirements are lower, and PSL and PR classifications are generally not required.

Certification requirements are relatively relaxed, making it suitable for low- and medium-risk environments.

2. Design and Structure
API 6A Gate Valve
Valve body construction: Typically constructed using a one-piece forging process, the valve body boasts high material strength and a dense internal structure, capable of withstanding extreme pressures and temperatures.
Sealing method: Primarily metal-to-metal sealing, it maintains a reliable seal under high pressure, high temperature, sand-laden, and corrosive media. Some valves utilize elastic or composite sealing structures for low-pressure applications.
Valve disc type: Commonly a parallel gate or double-disc design offers low opening and closing forces and high flow capacity.
Pressure rating: Available from 2,000 psi to 20,000 psi.
Special design: Features stem packing, automatic seat compensation, and grease injection ports for easy on-site maintenance. Ordinary Gate Valve
Body Structure: Mostly cast, resulting in lower production costs, but the material density is not as good as forgings.
Seal: Mostly non-metallic seals (such as rubber or polytetrafluoroethylene (PTFE)), suitable for medium- and low-pressure applications such as water, gas, and oil.
Valve Disc: Commonly used are wedge-type or elastic wedge-type discs, which are simple to manufacture and suitable for general use.
Pressure Rating: Generally ranges from PN16 (approximately 200 psi) to PN100 (approximately 1450 psi), significantly lower than API 6A.
Design Requirements: No API 6A-specific wellhead features, such as grease ports and double seals.

3. Operating Environment
API 6A Gate Valves
Specially used in the oil and gas industry, including:
Wellheads
Christmas Trees
High-pressure gathering and transportation manifolds
Offshore drilling platforms
The operating environment is extremely demanding: high pressure, high temperature, low temperature, and fluids containing CO₂, H₂S, sand, and corrosive fluids.
Valve sealing performance, safety, and reliability are extremely demanding; any failure could result in serious accidents such as blowouts and explosions.
Ordinary gate valves
Commonly used in municipal water supply and drainage, HVAC, industrial pipelines, power plant steam, food, and pharmaceutical applications.
The operating conditions are relatively mild: mostly conveying mediums at ambient temperature and pressure or at medium to low pressures.
Even if a leak or failure occurs, the risk is generally low, and maintenance and replacement are easy.

4. Cost and Maintenance
API 6A Gate Valve
Cost: Manufacturing and purchase prices are high because they require high-strength alloy steel (such as AISI 4130, AISI 410, Inconel 625), which undergoes rigorous heat treatment and testing.
Maintenance:
Regular pressure testing and leak checks are required.
Some products are designed with grease injection ports and online seat replacement capabilities, facilitating quick maintenance during wellhead operations.
Maintenance personnel must possess specialized knowledge and comply with API and oil company safety regulations.
Ordinary Gate Valve
Cost: Relatively low, primarily made of cast iron, carbon steel, or stainless steel.
Maintenance:
Simple structure, easy to repair or replace.
Parts are widely compatible and can be replaced at low cost.
No complex regular inspections are required; repairs are generally only required when a malfunction occurs.