API 6A & 16A Bonnet Bolts – API 20E BSL-3 Critical Fasteners for Oil and Gas
- Jan 15, 2025
- 4 min read
Updated: 5 days ago
Bonnet bolts are critical fasteners for oil and gas well control equipment.
These heavy-duty bolts secure the bonnets (covers) on API 6A wellhead and gate valves and the closures on API 16A Blowout Preventers (BOPs), containing extreme pressures.
To ensure safety and compliance, API 20E BSL-3 bolting requirements now govern offshore BOP closure bolting under API 16A, with API 6A bolting levels scaling by Product Specification Level (PSL). 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 valve and API 16A BOP bolting applications.
The Role of Bonnet Bolts in BOPs
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 6AÂ (Wellhead and Tree Equipment) and API Spec 16AÂ (Drill-through Equipment, including BOPs) both mandate that pressure-retaining and closure bolting meet the requirements of API 20E / API 20F.
Under API Spec 16A 4th Edition (Table 6), pressure-retaining and closure bolting on surface and subsea BOPs must meet API 20E / 20F BSL-3, while land-based BOP service requires BSL-2. Under API Spec 6A 21st Edition (Table 15), the required Bolting Specification Level scales with the equipment's Product Specification Level - PSL 1 to PSL 3 require BSL-1 (20E) / BSL-2 (20F), while PSL 4 closure bolting over 2½ in. nominal diameter requires BSL-3. Bolts are marked "20E3" on the head to confirm BSL-3 compliance and full traceability.
These standards were introduced following industry bolt failures on critical BOP and wellhead equipment. Today, any bolting used for offshore closure or pressure-retaining duty that does not meet the applicable BSL would be considered non-compliant with API 6A / 16A requirements.
API 20E BSL-3 Bolting Requirements
API Spec 20EÂ 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-3Â 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)Â 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 43Â
ASTM A194 GRADE 2HM
ASTM A194 GRADE 7M
ASTM A540 GRADE B22
ASTM A540 GRADE B23
API 20F Bolting Materials Â
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 R30035Â work strengthen only
UNS R30035Â 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.
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