API 6A & 16A Bonnet Bolts – API 20E BSL-3 Critical Fasteners for Oil and Gas

Dan Pearce
Jan 15
3 min read

Bonnet bolts are critical fasteners for oil and gas well control equipment. These heavy-duty bolts secure the bonnets (covers) on API 6A wellhead valves and API 16A Blowout Preventers (BOPs), containing extreme pressures. To ensure safety and compliance, API 20E BSL-3 standards now govern BOP bonnet bolting, requiring the highest level of quality and reliability. Below, we summarise the role of bonnet bolts, the key API standards, what API 20E BSL-3 entails, and how Energy Bolting delivers fully certified bonnet bolts for API 6A BOP bolting applications.

The Role of Bonnet Bolts in BOPs

Engineered for Absolute Reliability: API 20E BSL-3 Bonnet Bolts for Pressure Integrity in Blowout Preventers

Bonnet bolts fasten the BOP’s bonnet or door to the main body, forming a pressure-containing closure. They hold critical components (like ram assemblies or valve bonnets) in place against well pressure. Because a bonnet bolt failure could lead to a loss of well control (release of wellbore fluids), these bolts are classified as critical closure bolting . In operation, bonnet bolts endure high loads, cyclical stresses, and harsh environments, making their strength and integrity vital for blowout preventer (BOP) performance and safety.

Relevant API Standards for BOP Bolting

Bonnet bolt integrity is critical to maintaining pressure control in high-risk drilling operations.

Modern API equipment standards explicitly address bonnet bolt requirements. API Spec 6A (Wellhead and Christmas Tree Equipment) and API Spec 16A (Drill-through Equipment, including BOPs) mandate that pressure-retaining and closure bolts (such as bonnet bolts) meet the requirements of API 20E / API 20F. In the latest editions, Bolting Specification Level 3 (BSL-3) is required for all offshore BOP closure bolting. This means bonnet bolts for offshore API 6A/16A equipment must be manufactured and marked to API 20E BSL-3 (stamped “20E3” on the bolt head) to ensure full traceability and compliance. These standards were introduced after industry bolt failures, and today any non-BSL-3 bolts used for offshore closure or pressure retaining purposes would be considered non-compliant with API 6A/16A requirements.

API 20E BSL-3 Bolting Requirements

API Spec 20E defines how critical alloy/carbon steel bolts must be produced when required by API 6A, 16A, or similar standards. It establishes three quality levels (BSL-1, BSL-2, BSL-3), with BSL-3 as the highest tier. BSL-3 demands stringent technical and quality controls: advanced material specifications, thorough heat-treatment procedures, 100% non-destructive examination (e.g. ultrasonic inspection), impact testing, and detailed documentation for each lot. The highest criticality level (BSL-3) is reserved for applications where bolt failure is not an option.

In practical terms, a BSL-3 bonnet bolt has been proven through testing and quality assurance to withstand the extreme conditions of a BOP – if one of these bolts were to fail, it could result in an immediate hydrocarbon release.

API 20E BSL-3 provides assurance that bonnet bolts will perform reliably. Only manufacturers licensed by API can produce BSL-3 monogrammed bolts Bolts are individually stamped with: manufacturer ID, API 20E3, material grade, date of manufacture, unique trace code, API licence number and the API Monogram ® Additional customer specific requirements (part number/ serial markings) can be added.

Energy Bolting’s BSL-3 Certification & Capabilities

Energy Bolting Limited is a specialised fastener manufacturer - licenced to manufacture API 20E BSL-3 bolting. We are API Q1 certified and hold API Monogram licenses:

API 20E-0098 BSL-1, BSL-2, BSL-3 carbon & alloy steel bolting
API 20F-0048 BSL-2 & BSL-3 corrosion resistant bolting

We are licenced to mark our bonnet bolts with API 20E markings, assuring you of compliance with API 6A/16A requirements.

Energy Bolting Offers:

Monogrammed Product
Urgent Production From Raw Material Stock
Flexible Service
Highest Criticality Product - BSL-3

API 20E Bolting Materials ASTM A193 GRADE B7

ASTM A193 GRADE B7M

ASTM A320 GRADE L7

ASTM A320 GRADE L7M

ASTM A320 GRADE L43

ASTM A194 GRADE 2H

ASTM A194 GRADE 7 ASTM A194 GRADE 43

ASTM A194 GRADE 2HM

ASTM A194 GRADE 7M

ASTM A540 GRADE B22

ASTM A540 GRADE B23

API 20F Bolting Materials

ASTM A453 GRADE 660 CLASS D

API 6ACRA N07716 120K, 140K

API 6ACRA N07718 120K, 140K

API 6ACRA N07718 140K

API 6ACRA N07725 120K

API 6ACRA N09925 110K

API 6ACRA N09935 110K

API 6ACRA N09945 125K

API 6ACRA N09946 140K

API 6ACRA N09945 125K, 140K

API 6ACRA N09946 140K, 150K 160K

UNS R30035 work strengthen only

UNS R30035 work strengthen and aged

Do you have a demand for API 20E Bonnet Bolts? We export worldwide!

This content is for general information only and does not constitute technical advice. Specifications and requirements should be verified against the latest applicable standards. Energy Bolting is not responsible for any decisions or actions taken based on this summary.