API 20E vs API 20F Bolting Standards: Key Differences and Selection Criteria

Introduction

In the oil and gas industry, bolting integrity is critical for safety and reliability. The American Petroleum Institute (API) has developed two key standards for bolting: API 20E (for carbon and alloy steel stud bolts) and API 20F (for corrosion-resistant alloy bolting). While both aim to ensure quality and performance, they differ in scope, material requirements, testing, and certification. This article provides a detailed comparison to help procurement engineers and project managers select the appropriate standard for their applications, especially in high-pressure high-temperature (HPHT) environments.

API 20E vs API 20F: Scope and Application

API 20E covers the specification for carbon and alloy steel stud bolts, hex bolts, and heavy hex nuts used in oil and gas pressure-containing equipment. It applies to materials such as ASTM A193 Grade B7, B16, and B7M. The standard is intended for bolting in general service, including moderate temperatures and pressures.

API 20F addresses corrosion-resistant alloy bolting, including materials like ASTM A193 Grade B8 (Class 1 and 2), B8M, and other stainless steels. It is designed for environments where corrosion resistance is critical, such as sour service (NACE MR0175/ISO 15156) and high-temperature applications.

Material Requirements Comparison

Both standards specify chemical composition, mechanical properties, and heat treatment. However, API 20F imposes stricter controls on corrosion resistance, including intergranular corrosion testing for stainless steels. API 20E focuses on strength and toughness at low temperatures (e.g., Charpy V-notch testing for B7).

Chemical Composition

API 20E allows a wider range of carbon and alloy steels, while API 20F limits elements to enhance corrosion resistance. For example, API 20F requires a minimum of 10.5% chromium for stainless steels.

Mechanical Properties

API 20E specifies tensile and yield strength requirements per grade. API 20F includes additional requirements for hardness control (e.g., HRC ≤ 22 for B8M Class 2) to prevent sulfide stress cracking.

Testing and Certification Differences

Both standards require testing such as tensile, hardness, and dimensional checks. However, API 20F mandates additional tests:

• Intergranular Corrosion Test (per ASTM A262 Practice E) for stainless steels.
• Impact Testing at low temperatures for certain grades.
• PMI (Positive Material Identification) for alloy verification.

API 20E may require Charpy impact testing for low-temperature service. Both standards require a certified material test report (MTR) per EN 10204 3.1 or 3.2.

When to Use API 20E vs API 20F

Selection depends on service conditions:

• API 20E: Use for non-corrosive environments, moderate temperatures (-20°F to 1000°F), and general pressure vessel and piping flanges.
• API 20F: Use for sour service (H₂S present), high temperatures above 1000°F, or where corrosion resistance is required (e.g., offshore, chemical processing).

Case Study: Selection for HPHT Application

An offshore HPHT well required bolting for a 15,000 psi Christmas tree. The environment contained H₂S and CO₂ at 350°F. API 20F was chosen with ASTM A193 B8M Class 2 (NACE compliant). The bolts passed intergranular corrosion and hardness tests. API 20E would not have been suitable due to insufficient corrosion resistance.

LOKRON Solution

LOKRON supplies both API 20E and API 20F certified bolting with full traceability. Our products include ASTM A193 B7/B16/B7M for API 20E and B8/B8M/B8T for API 20F. We provide EN 10204 3.1 documentation and third-party testing. For HPHT applications, we recommend API 20F with NACE compliance.

Frequently Asked Questions

1. Can API 20E bolts be used in sour service?

Only if the material is specifically qualified for sour service, such as ASTM A193 B7M. However, API 20F is generally preferred for sour environments.

2. What is the difference between API 20E and API 20F in terms of testing?

API 20F requires additional intergranular corrosion testing and PMI, while API 20E focuses more on impact testing for low temperatures.

3. Are API 20E and API 20F interchangeable?

No, they are designed for different service conditions. Using API 20E in a corrosive environment may lead to failure.

4. Do API 20F bolts require NACE compliance?

Not always, but for sour service, NACE MR0175/ISO 15156 compliance is typically specified. API 20F includes grades that meet these requirements.

5. What documentation is provided with LOKRON API bolts?

We provide EN 10204 3.1 inspection certificates, material test reports, and traceability records.

Summary

API 20E and API 20F serve different needs in oil and gas bolting. API 20E is for carbon/alloy steel in general service, while API 20F is for corrosion-resistant alloys in harsh environments. Proper selection based on service conditions is critical for safety and reliability. LOKRON offers both standards with full certification and expert guidance.