API 20E & API 20F: Oil and Gas Bolting Standards — 2025 Third Edition Guide

Why API 20E and API 20F Matter in 2025

The American Petroleum Institute's API 20E and API 20F standards govern the qualification, manufacture, and testing of bolting for critical oil and gas applications — from wellhead assemblies and blowout preventers to high-pressure/high-temperature (HPHT) subsea connectors. In March 2025, API published the Third Edition of both standards, introducing updated Bolting Service Level (BSL) requirements, expanded traceability provisions, and new requirements for HPHT and sour-service applications. For procurement engineers and EPC contractors, understanding these changes is essential: specifying pre-2025 edition requirements on new project packages may result in non-compliant deliveries and costly requalification.

Scope: What Equipment Requires API 20E / 20F Bolting?

API 20E covers alloy steel and carbon steel bolting for general petroleum and natural gas industry service. API 20F covers corrosion-resistant alloy (CRA) bolting — stainless steel, nickel alloys, and duplex grades — for corrosive service environments. Together, these standards apply to:

• Wellhead equipment — casing head flanges, tubing head flanges, christmas tree connections
• Blowout preventers (BOPs) — all bolted pressure-containing connections
• Subsea equipment — subsea trees, manifolds, flowline connectors, riser systems
• Surface production equipment — high-pressure separators, glycol contactors, compressor flanges
• HPHT applications — equipment with design pressure exceeding 103 MPa (15,000 psi) or temperature exceeding 177°C (350°F)

Both standards are mandatory when equipment is manufactured to API 6A (Wellhead and Christmas Tree Equipment), API 17D (Subsea Wellhead and Christmas Tree Equipment), API 16A (Drill-Through Equipment), or when referenced by project-specific purchase orders from operators such as Saudi Aramco, Shell, BP, or TotalEnergies.

Bolting Service Levels (BSL): The Core Framework

Both API 20E and API 20F organize requirements into three Bolting Service Levels, with increasing rigor from BSL-1 to BSL-3:

BSL Level	Application	Key Requirements	Typical Use
BSL-1	General service	Material certs, dimensional inspection, hardness testing per heat	Surface equipment, non-critical service
BSL-2	Elevated risk	BSL-1 + individual piece marking, enhanced mechanical testing, NDE on 10% of pieces	Wellhead flanges, BOP connections, production separators
BSL-3	Critical service	BSL-2 + 100% NDE, charpy impact testing, documented heat treatment records, third-party witness	HPHT equipment, subsea, sour service, safety-critical connections

The Third Edition (2025) introduces a new sub-category: BSL-3S for severe sour service applications, with hardness requirements now harmonised with NACE MR0175/ISO 15156-3 and mandatory hydrogen embrittlement testing under ASTM F1624 for CRA grades above 34 HRC.

API 20E: Key 2025 Third Edition Changes

1. Material Grade Expansion

The Third Edition adds explicit coverage for Gr. 660 (Alloy 718 / UNS N07718) and Gr. 725 (Alloy 725 / UNS N07725) nickel-base alloy bolting — previously specified by reference to ASTM B637 and project-specific requirements. This change reflects the growing use of high-strength nickel alloys in HPHT completion equipment where Alloy 718's tensile strength of 1,100 MPa and excellent corrosion resistance in H₂S-CO₂ environments justify the premium cost.

2. Traceability and Serialisation

BSL-2 and BSL-3 bolts must now carry unique serial numbers traceable to individual heat lot test certificates. The previous edition required heat lot identification; the Third Edition mandates piece-level traceability for BSL-3, enabling full documentation review against individual fastener performance under API 20E's "fitness for service" audit framework.

3. HPHT Supplementary Requirements

A new Section 9 establishes supplementary requirements for HPHT bolting (pressure ≥ 103 MPa or temperature ≥ 177°C). Key additions include mandatory stress relaxation testing at the maximum design temperature for alloy grades used above 150°C, and a minimum ductility requirement of 15% elongation for all HPHT-designated grades after final heat treatment.

API 20F: Corrosion-Resistant Bolting — 2025 Changes

API 20F covers CRA bolting in four material categories:

• Martensitic stainless steels — 410 SS, 13Cr types
• Austenitic stainless steels — 316L, 317L, 904L
• Duplex and super-duplex stainless steels — 2205, 2507, Zeron 100
• Nickel-base alloys — Alloy 625, Alloy C-276, Alloy 718, Alloy 825

The 2025 Third Edition adds two significant requirements for duplex and super-duplex grades:

1. PREN (Pitting Resistance Equivalent Number) verification — Duplex 2205 must demonstrate PREN ≥ 35; Super-Duplex 2507 must demonstrate PREN ≥ 40, calculated from actual heat chemistry as PREN = %Cr + 3.3(%Mo) + 16(%N). This prevents underperforming heats from being used in chloride-aggressive subsea service.
2. Ferrite content measurement — All duplex grade bolts at BSL-2 and BSL-3 must have ferrite content verified (40–60% austenite/ferrite balance) using a calibrated ferritescope. This requirement addresses the known risk of intermetallic phase precipitation during inadequate solution annealing.

Sour Service: Alignment with NACE MR0175

For applications subject to H₂S partial pressure ≥ 0.0003 MPa, API 20E's Third Edition now explicitly cross-references ISO 15156-3 Table A.4 for maximum hardness limits by alloy family. Key limits for common grades in sour service:

Material	Max Hardness (Sour Service)	Standard Reference
ASTM A193 B7M (4140 Cr-Mo)	22 HRC (237 HB)	NACE MR0175/ISO 15156-2
Duplex 2205 (UNS S31803)	28 HRC (301 HB)	NACE MR0175/ISO 15156-3
Super-Duplex 2507 (UNS S32750)	32 HRC (336 HB)	NACE MR0175/ISO 15156-3
Alloy 625 (UNS N06625)	35 HRC (331 HB)	NACE MR0175/ISO 15156-3
Alloy 718 (UNS N07718)	40 HRC (392 HB)	NACE MR0175/ISO 15156-3

Supplier Qualification: What to Verify

When qualifying a fastener supplier against API 20E or API 20F, procurement engineers should verify: API Monogram License at api.org/monogram; MTRs with full heat chemistry and mechanical test results at the specified BSL; heat treatment records for BSL-3; and third-party inspection witness certificates from an approved body (SGS, Bureau Veritas, Intertek, TÜV Rheinland). LOKRON supplies API 20E and API 20F compliant bolting under ISO 9001:2015. Our standard documentation package includes heat-specific MTRs, dimensional inspection certificate, hardness survey, and — for BSL-3 orders — third-party inspection certificates. Contact our technical team with BSL level, grade requirements, and quantity for a formal proposal.