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API Bull E1-1990 (with Errata 1991): Guidelines for Subsea Wellhead and Christmas Tree Equipment
Understanding the Scope, Technical Requirements, and Compliance Notes for API Bulletin E1
API Bulletin E1 (1990), together with its 1991 errata, provides essential guidance for the application of API Specification 6A (Wellhead and Christmas Tree Equipment) to subsea systems. As the oil and gas industry expanded into deeper waters during the late 1980s and early 1990s, operators and manufacturers recognized that the existing API 6A requirements — originally developed for surface and platform applications — needed augmentation to address the unique challenges of subsea service. This bulletin consolidates recommended practices for design, material selection, testing, and quality assurance, ensuring reliable performance in high-pressure, corrosive, and remote subsea environments.
Scope and Purpose
API Bull E1 defines the additional engineering and quality requirements that apply when API 6A equipment is intended for subsea service. The bulletin covers all pressure-containing and pressure-control components of subsea wellheads, Christmas trees, and related equipment. Its primary objectives are:
- To identify environmental and operational conditions unique to subsea service (e.g., hydrostatic pressure, low ambient temperatures, seawater corrosion, and limited accessibility for intervention).
- To establish minimum supplementary requirements for material selection, design validation, and testing beyond those in API 6A.
- To provide a framework for documentation and traceability to support lifecycle integrity management.
Tip: While API Bull E1 does not replace or supersede API 6A, it is referenced in many project specifications and is considered a key deliverable for subsea qualification programs.
The bulletin applies to equipment rated for pressures up to 20,000 psi and is particularly relevant for deepwater and harsh environment developments. It encourages a risk-based approach, allowing designers to adapt the requirements based on the severity of the service conditions.
Technical Requirements
API Bull E1 introduces several modifications and enhancements to the base API 6A requirements. The major technical areas addressed include:
Material Selection and Hardenability
Subsea equipment must resist sulfide stress cracking (SSC), hydrogen-induced cracking (HIC), and seawater corrosion. The bulletin specifies stricter limits on material hardness, chemical composition, and heat treatment compared to API 6A. For instance, carbon and low-alloy steels used in subsea pressure-containing parts are required to have a maximum hardness of HRC 22 (versus HRC 23 for surface equipment). Additional requirements for Corrosion-Resistant Alloys (CRAs) are provided, including pitting resistance equivalent number (PREN) thresholds.
| Parameter | API 6A (Surface) | API Bull E1 (Subsea) |
|---|---|---|
| Maximum Hardness (Pressure-Containing Parts) | HRC 23 | HRC 22 |
| Minimum PREN for CRAs | Not required | ≥ 40 (for seawater service) |
| Hydrogen Charging Test | Not required | Per NACE TM0284 |
| Elastomeric Seal Qualification | Heat-aging test | Heat-aging + rapid gas decompression (RGD) test |
| External Corrosion Protection | Coating per vendor standard | Coating + cathodic protection design compatibility |
Design Validation and Testing
The bulletin mandates additional validation procedures to confirm the equipment’s ability to withstand the subsea environment. Key tests include:
- Combined Load Testing: Simultaneous application of internal pressure, axial load, bending moment, and external hydrostatic pressure to simulate installation and service conditions.
- Functional Cycling at Low Temperature: Performance of operational cycles (opening/closing, connection make‑up) at the minimum design temperature (typically -20°C or lower).
- External Pressure Testing: Verification of sealing integrity of external seals (e.g., body flanges, bonnet gaskets) under external hydrostatic head.
Important: The 1991 errata corrected a critical oversight in the original bulletin: it clarified that external pressure testing must be performed with simulated seawater at a temperature of 2–5 °C to avoid unrealistic thermal effects on seal materials.
Quality Assurance and Traceability
API Bull E1 requires a higher level of documentation than API 6A. Manufacturers must submit a Subsea Qualification Plan that details all design verification activities, inspection hold points, and materials traceability. The bulletin also recommends the use of independent third‑party inspection for critical welds and nondestructive examinations (NDE).
Implementation and Application
Adoption of API Bull E1 is voluntary but is widely specified by operators as a contractual requirement for subsea equipment. The bulletin is intended to supplement — not replace — other applicable standards such as NACE MR0175/ISO 15156 for materials in H₂S environments and API 17D for subsea wellhead systems.
Recommended Implementation Steps
- Gap Analysis: Compare existing API 6A documentation against Bull E1 requirements, focusing on hardness testing, CRA PREN, and RGD testing of seals.
- Material Upgrading: Where existing components do not meet the stricter hardness limits or PREN thresholds, source alternative materials or modify heat treatment procedures.
- Test Protocol Revision: Revise factory acceptance test (FAT) plans to include combined load and external pressure tests as specified in the bulletin.
- Qualification Revalidation: If the equipment design has changed since the original qualification, repeat the required tests or justify via engineering analysis.
Best Practice: Several industry groups have used API Bull E1 as the basis for more detailed company specifications. It is advisable to incorporate the bulletin by reference in project technical specifications.
Compliance and Certification
There is no formal API monogramming program for API Bull E1. Instead, compliance is demonstrated through a combination of manufacturer declarations, third‑party verification reports, and operator acceptance. The following documentation should be maintained:
- Material Test Reports (MTRs) for all pressure‑containing components with hardness results and chemical analysis.
- Qualification Test Reports for combined load, external pressure, and low‑temperature cycling.
- Traceability Records for all elastomeric and non‑metallic seals, including batch numbers and RGD test data.
Caution: The 1991 errata made several mandatory corrections. Any equipment qualified prior to the errata must be re‑evaluated for external pressure testing and material hardness compliance. Using the original 1990 version alone may result in non‑conformity with current industry practices.
Regulatory bodies such as the U.S. Bureau of Safety and Environmental Enforcement (BSEE) and international equivalents may reference API Bull E1 in their regulations for subsea well control equipment. While the bulletin itself is not a law, operators are expected to follow recognized and generally accepted good engineering practices (RAGAGEP), which often include the requirements of this bulletin.
Frequently Asked Questions
Q: What is the difference between API 6A and API Bull E1?
A: API 6A is the core specification for wellhead and Christmas tree equipment used in surface and platform applications. API Bull E1 does not replace API 6A; instead, it provides supplementary requirements and recommendations specifically for equipment installed in subsea environments, where external hydrostatic pressure, low temperatures, and limited access demand more rigorous design validation, material selection, and testing.
A: API 6A is the core specification for wellhead and Christmas tree equipment used in surface and platform applications. API Bull E1 does not replace API 6A; instead, it provides supplementary requirements and recommendations specifically for equipment installed in subsea environments, where external hydrostatic pressure, low temperatures, and limited access demand more rigorous design validation, material selection, and testing.
Q: What changes were introduced in the 1991 errata?
A: The 1991 errata corrected several technical inconsistencies in the original 1990 bulletin. The most significant change was adding the requirement for external pressure testing in actual or simulated seawater at 2–5 °C. It also adjusted some hardness testing acceptance criteria and clarified the definition of “pressure‑containing part” for subsea equipment, ensuring alignment with emerging industry practices.
A: The 1991 errata corrected several technical inconsistencies in the original 1990 bulletin. The most significant change was adding the requirement for external pressure testing in actual or simulated seawater at 2–5 °C. It also adjusted some hardness testing acceptance criteria and clarified the definition of “pressure‑containing part” for subsea equipment, ensuring alignment with emerging industry practices.
Q: Is API Bull E1 still relevant today, or has it been superseded?
A: API Bull E1 remains a referenced document in many industry specifications, though some of its content has been incorporated into newer standards such as API 17D (Design and Operation of Subsea Production Systems) and ISO 13628‑4. However, because the bulletin offers focused guidance on the application of API 6A to subsea equipment, it is still used as a reference for legacy qualification programs and for equipment where full compliance with newer standards may not be required.
A: API Bull E1 remains a referenced document in many industry specifications, though some of its content has been incorporated into newer standards such as API 17D (Design and Operation of Subsea Production Systems) and ISO 13628‑4. However, because the bulletin offers focused guidance on the application of API 6A to subsea equipment, it is still used as a reference for legacy qualification programs and for equipment where full compliance with newer standards may not be required.
Q: Does API Bull E1 require mandatory certification by a third party?
A: No, the bulletin does not mandate third‑party certification. However, it recommends independent verification for critical tests (e.g., combined load testing, RGD testing). Many operators require compliance with Bull E1 and often request a statement of compliance together with test reports from a recognized independent laboratory. Certification from a body such as DNV or ABS may be accepted as evidence of compliance.
A: No, the bulletin does not mandate third‑party certification. However, it recommends independent verification for critical tests (e.g., combined load testing, RGD testing). Many operators require compliance with Bull E1 and often request a statement of compliance together with test reports from a recognized independent laboratory. Certification from a body such as DNV or ABS may be accepted as evidence of compliance.
Published 2026 — This article provides a general technical overview of API Bull E1-1990 and its 1991 errata. For detailed compliance, users should consult the full bulletin text.