API 20E vs API 20F: Oil and Gas Bolting Standards Comparison

Introduction to API 20E and API 20F

The American Petroleum Institute (API) has developed two key standards for bolting used in the oil and gas industry: API 20E (Alloy and Carbon Steel Bolting) and API 20F (Corrosion-Resistant Alloy Bolting). These standards specify requirements for the qualification, production, and documentation of bolting materials to ensure reliability in critical service environments. While both aim to enhance safety and performance, they differ significantly in scope, material types, and testing requirements. This article provides a detailed comparison to help procurement engineers and project managers select the appropriate standard for their applications.

Key Differences in Scope and Requirements

API 20E: Alloy and Carbon Steel Bolting

API 20E covers bolting made from carbon steel, alloy steel, and high-temperature materials such as ASTM A193 B7, B16, and A320 L7. It is primarily intended for general-purpose and high-temperature service in accordance with ASME B16.5 and ASME VIII. The standard includes requirements for material traceability, heat treatment, mechanical testing, and quality control. API 20E is often specified for flanged connections, pressure vessels, and valve assemblies.

API 20F: Corrosion-Resistant Alloy Bolting

API 20F addresses bolting made from corrosion-resistant alloys (CRAs) such as stainless steels (e.g., ASTM A193 B8, B8M), nickel alloys, and other materials resistant to sour service (NACE MR0175/ISO 15156). This standard is designed for environments where hydrogen sulfide (H₂S) or other corrosive agents are present. API 20F includes additional requirements for corrosion testing, hardness control, and sulfide stress cracking (SSC) resistance.

Comparison Table

Material and Testing Requirements

API 20E Material Requirements

API 20E mandates that bolting materials conform to ASTM or other recognized standards. Key requirements include:

• Chemical composition per applicable ASTM specification.
• Heat treatment (e.g., quenching and tempering for B7).
• Mechanical testing: tensile, yield, elongation, reduction of area, and hardness.
• Impact testing for low-temperature service (e.g., A320 L7).
• Non-destructive examination (NDE) such as magnetic particle or ultrasonic inspection.

API 20F Material Requirements

API 20F imposes additional requirements due to the corrosive environment:

• Corrosion resistance verified by testing per NACE TM0177 (SSC) or TM0284 (HIC).
• Hardness control: maximum hardness limits (e.g., ≤ HRC 22 for certain materials).
• Microstructure examination to ensure proper phase balance.
• Stress corrosion cracking (SCC) testing for specific alloys.
• Enhanced traceability from melt to final product.

When to Specify API 20E vs API 20F

Choosing between API 20E and API 20F depends on the service conditions:

• API 20E is suitable for non-sour, general service applications such as standard flanges, pressure vessels, and piping systems where corrosion is not a primary concern. It is also used for high-temperature bolting (e.g., B16).
• API 20F is required when the bolting will be exposed to sour gas (H₂S) or corrosive chemicals. Typical applications include subsea equipment, wellhead components, and chemical processing units. API 20F is often mandated by project specifications for critical sour service.

Note that some projects may require a combination: for example, stud bolts in sour service must meet API 20F, while nuts may be specified per API 20E if they are not exposed to the corrosive environment.

LOKRON's Compliance and Capabilities

LOKRON (Suzhou Fulida) is fully equipped to supply bolting that meets both API 20E and API 20F requirements. Our quality management system is certified to ISO 9001 and IATF 16949, and we hold PED 2014/68/EU certification for pressure equipment components. We offer:

• API 20E bolting: ASTM A193 B7, B16, A320 L7 with full traceability and EN 10204 3.1 documentation.
• API 20F bolting: ASTM A193 B8, B8M, and other CRAs with NACE MR0175 compliance and corrosion testing.
• Custom solutions: We can produce bolting to customer-specific requirements, including special dimensions, coatings, and additional testing.

Our experienced team ensures that every batch meets the stringent requirements of API standards, providing reliability and safety for your critical applications.

Frequently Asked Questions

1. What is the main difference between API 20E and API 20F?

API 20E covers carbon and alloy steel bolting for general service, while API 20F covers corrosion-resistant alloy bolting for sour service environments.

2. Can API 20E bolting be used in sour service?

Only if the material is specifically qualified per NACE MR0175 and meets additional hardness and testing requirements. In most cases, API 20F is preferred for sour service.

3. Are API 20E and API 20F mandatory for oil and gas applications?

They are not mandatory by law but are often required by project specifications, especially for critical service. Many operators mandate API 20E/20F for bolting in pressure-containing equipment.

4. Does LOKRON supply API 20E and API 20F certified bolting?

Yes, LOKRON supplies both API 20E and API 20F compliant bolting with full documentation, including EN 10204 3.1 and NACE certificates.

5. What testing is required for API 20F bolting?

API 20F requires corrosion testing (SSC, HIC), hardness testing, mechanical testing, and enhanced traceability. Specific tests depend on the material grade and service conditions.

Summary

API 20E and API 20F are essential standards for bolting in the oil and gas industry. API 20E is suitable for general and high-temperature service, while API 20F is designed for corrosive and sour environments. Understanding the differences helps ensure the correct specification for safety and reliability. LOKRON offers comprehensive bolting solutions compliant with both standards, backed by certifications and decades of experience.