ANSI API RP 17C-2002 (2010): Recommended Practice for Tethering Components for Subsea Production Systems

ANSI API RP 17C-2002 (2010) is a recommended practice published by the American Petroleum Institute that provides guidelines for the engineering, material selection, manufacturing, testing, and documentation of tethering components used in subsea production systems. This document, reaffirmed in 2010, serves as the primary reference for ensuring the structural integrity and long-term reliability of components such as connectors, clamps, buoyancy modules, and other hardware that form part of the tethering system for floating production units and subsea structures.

Scope and Applicability

The scope of ANSI API RP 17C-2002 (2010) covers all load-bearing and positioning components used in subsea tethering systems, including but not limited to:

• Connection hardware (e.g., shackles, links, swivels)
• Clamps and grippers for flexible pipes and umbilicals
• Buoyancy modules and their attachment systems
• Foundation connectors and pile top interfaces
• Riser tensioner components and tether termination assemblies

The recommended practice applies to the entire lifecycle of tethering components—from conceptual design and material selection through fabrication, installation, and in-service monitoring. It is intended for use by engineers, manufacturers, operators, and certification bodies involved in subsea production systems.

Technical Requirements

Design Principles

The recommended practice establishes design criteria based on limit state methodology similar to ISO 19902 or API RP 2A-WSD, but adapted for the specific failure modes of tethering components. Key design requirements include:

• Load classification: Design loads are categorized into operating, extreme, and accidental conditions, with corresponding safety factors defined in Section 5 of the document.
• Fatigue analysis: All components must undergo S-N curve based fatigue assessment, including the effects of corrosion, fretting, and installation damage.
• Redundancy and robustness: Tethering systems must be designed with sufficient redundancy such that failure of any single component does not lead to progressive collapse.
• Material selection: Materials must resist hydrogen embrittlement, stress corrosion cracking, and sulfide stress cracking in accordance with NACE MR0175/ISO 15156.

Material Qualification

Annex A of the standard provides detailed material qualification procedures. Materials are categorized based on service condition severity (CS I, II, III) with increasing testing requirements. The table below summarizes the mandatory tests for each category:

The standard also requires traceability of material from mill to finished component, with documented mill certificates and positive material identification (PMI) for alloyed steels.

Proof Load Testing and Factory Acceptance

Each production unit of a tethering component (with the exception of mass-produced non-load-bearing items) must be subjected to a proof load test of 1.5 times the design maximum load. The standard specifies acceptance criteria including permanent set limits (≤0.2% of original dimension after unloading) and no visual cracking or leakage. For hydraulic components, pressure tests at 1.5 times working pressure and zero leakage are required.

The table below lists typical proof load factors for various component types:

MBL = Minimum Breaking Load; WP = Working Pressure

Implementation Highlights

Adopting ANSI API RP 17C-2002 (2010) in subsea projects involves a systematic approach to engineering, procurement, and quality assurance. The following elements are critical to successful implementation:

• Design Basis Document (DBD): A project-specific DBD must be created that specifies design loads, environmental conditions, material categories, and corrosion allowance. This document is the starting point for all component designs.
• Verify Fatigue Life: Use finite element analysis (FEA) for complex geometries and follow the S-N curve methodology as detailed in Annex B of the standard.
• Manufacturing Surveillance: Employ dedicated witness points during fabrication, especially for welding, heat treatment, and non-destructive examination (NDE). RT/UT/MT for critical welds.
• Traceability System: Implement a system that tracks each component from raw material through final test, with unique serial numbers and digital records.
• Installation Qualification: Perform pre-installation testing of all connectors, including on-bottom stability and torque verification.

Compliance Notes

Compliance with ANSI API RP 17C-2002 (2010) is typically verified through a third-party certification body such as DNV, Lloyds, or ABS. The certification process includes design review, validation of qualification tests, and audit of the manufacturing facility. Key points:

• Type Approval: Many certifiers offer type approval programs based on API RP 17C. This reduces project-specific verification if the component design is already approved.
• Project-Specific Validation: Even with type approval, a project-specific validation is required to confirm interface compatibility and site-specific loads.
• Documentation: A complete documentation package must be submitted including design reports, material certificates, manufacturing records, NDE reports, and test results. The standard recommends a “Design and Manufacturing Record” (DMR) folder.
• In-Service Inspection: The standard recommends an in-service inspection plan at intervals not exceeding five years for retrievable components. For non-retrievable components, condition monitoring (e.g., strain or cathodic potential) should be used.

Frequently Asked Questions