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API RP 1117-2008 (2013): Recommended Practice for Movement of In-Service Pipelines
Engineering Guidelines for Safe Relocation and Adjustment of Operating Pipelines
Introduction and Scope
API RP 1117-2008 (2013), officially titled API Recommended Practice 1117, Second Edition, November 2008, Reaffirmed June 2013, provides engineering guidelines for the movement of pipelines that remain in service during the relocation operation. This recommended practice applies to onshore and offshore pipelines transporting liquid hydrocarbons, natural gas, or other regulated fluids. It addresses scenarios such as lifting, lowering, lateral shifting, and adjustment of pipelines to accommodate new construction, grade changes, or settlement corrections. The standard covers both aboveground and buried pipelines, with emphasis on maintaining structural integrity, preventing leaks, and ensuring safe operation throughout and after the movement.
While primarily intended for carbon steel pipelines, the principles in API RP 1117 can be adapted to other metallic pipelines with appropriate engineering assessment. The standard references and aligns with other industry codes such as ASME B31.4 (Pipeline Transportation Systems for Liquids and Slurries) and ASME B31.8 (Gas Transmission and Distribution Piping Systems), as well as API 1102 (Steel Pipelines Crossing Railroads and Highways) and various coating and cathodic protection standards.
Technical Requirements
Stress and Strain Limits
A key technical focus of API RP 1117 is defining allowable stress and strain levels during pipeline movement. The standard prohibits movement that would cause yielding, buckling, or loss of containment. The following limits are typically applied:
- Longitudinal Combined Stress: The sum of stress due to internal pressure and bending must not exceed a specified percentage of the specified minimum yield strength (SMYS), typically 90% for movement operations.
- Bending Strain: Maximum allowable bending strain is limited to prevent local buckling and wrinkling. For typical carbon steel pipelines, the recommended maximum outer fiber bending strain is 1.5% to 2% depending on diameter-to-thickness ratio and operating conditions.
- Ovality: Cross-sectional distortion (ovality) must be controlled to avoid excessive stress concentrations and clearance issues. Ovality limits are usually kept below 3% to 5%.
- Combined Stress and Strain: Hoop stress from operating pressure is combined with bending stresses using appropriate failure criteria (e.g., von Mises or Tresca).
The table below summarizes typical allowable limits specified or referenced in API RP 1117 for common pipeline movement scenarios.
| Parameter | Condition | Allowable Limit |
|---|---|---|
| Longitudinal Combined Stress | Sustained operating pressure during movement | ≤ 90% of SMYS |
| Bending Strain (outer fiber) | Cold bending (no thermal stress relief) | ≤ 2% for D/t ≥ 40; ≤ 1.5% for D/t < 40 |
| Ovality (after movement) | Pipe cross-section | ≤ 5% of nominal diameter |
| Hoop Stress | During movement (operating pressure reduced) | ≤ 50% of SMYS |
| Coatings Strain | Damage to field-applied coatings | < 1% elongation (if concrete coated, < 0.5%) |
| Pipe Wall Thinning | Corrosion allowance reduction | Not less than required minimum |
Movement Procedures
API RP 1117 outlines step-by-step procedures for different movement types. For buried pipelines, careful excavation is required to avoid structural damage. The pipeline must be exposed over a sufficient length to accommodate the required movement without inducing sharp bends. For aboveground pipelines, supports must be properly positioned and adjusted.
The standard requires the following steps prior to any movement:
- Engineering assessment, including stress analysis using recognized methods (such as beam theory or finite element analysis).
- Review of pipeline condition: casing, coating, cathodic protection, and prior repairs.
- Determination of safe operating conditions (pressure reduction if needed).
- Planning of movement sequence, speed, and monitoring.
- Traffic and safety controls for aboveground operations.
Inspection and Monitoring
During movement, continuous monitoring of pipe strain, movement distance, and support positions is essential. The standard recommends real-time strain gauging for critical movements. Visible signs of surface damage, coating disbondment, or change in ovality must be documented. Post-movement inspection must include:
- Visual inspection of pipe surface and coating.
- Measurement of ovality and any residual deformation.
- Leak testing (if required by operating conditions).
- Verification of cathodic protection system continuity and effectiveness.
- Backfill and compaction inspection for buried pipelines.
Implementation Highlights
Successful application of API RP 1117 demands coordination between engineering, construction, and pipeline operations personnel. Key implementation considerations include:
- Pressure Reduction: In many cases, reducing internal pressure during movement lowers stress levels, increasing the allowable movement range. The standard provides guidance on conditions for pressure reduction and for operating the pipeline during movement.
- Coating Protection: For coated pipes, especially those with concrete weight coating or thermal insulation, movement can cause coating damage. The standard recommends using pads, slings, and rollers to minimize friction and stress concentrations. Inspection of coating after movement is mandatory.
- Documentation: Detailed documentation of the engineering analysis, movement plan, monitoring records, and inspection results is required to demonstrate compliance with the recommended practice and to support pipeline integrity management programs.
- Qualified Personnel: Movement operations must be directed by personnel experienced in pipeline engineering and construction. Engineering analysis should be performed or reviewed by a licensed professional engineer.
Tip: When planning a pipeline movement, conduct a thorough feasibility assessment including soil conditions, pipeline design, and operating factors. Early identification of constraints reduces project delays.
Warning: Movement of an in-service pipeline without proper stress analysis can lead to catastrophic failure. Always consult with qualified pipeline engineering specialists.
Success: Following API RP 1117 procedures ensures that pipeline integrity is maintained, minimizing downtime and environmental risk during relocation.
Compliance and Regulatory Notes
API RP 1117 is a recommended practice and not a mandatory code. However, it is widely adopted by pipeline operators and regulators as an industry-accepted standard of care. In the United States, regulations under 49 CFR Part 192 (gas) and Part 195 (liquids) require operators to follow good engineering practices during pipeline modifications. Compliance with API RP 1117 can be used to demonstrate that the movement operation meets regulatory requirements.
Key compliance aspects include:
- Documenting the engineering analysis and movement plan.
- Ensuring that all personnel involved in movement are trained and qualified.
- Performing post-movement integrity verification, including leak tests and cathodic protection checks.
- Recording movement parameters and inspection results in a permanent file.
The standard also aligns with international standards such as ISO 13623 and ISO 21809 for pipeline design and coating. For operators outside the US, API RP 1117 serves as a reference for developing movement procedures that meet local regulations.
Critical: Failure to follow industry recommended practices may expose operators to liability in the event of an incident. Regulatory agencies may reference API RP 1117 when investigating pipeline movements.
Frequently Asked Questions
Q: What types of pipeline movement does API RP 1117 cover?
A: The standard covers movement of in-service pipelines, including lateral shifting, vertical lifting or lowering, and angular adjustments. It applies to both buried and aboveground pipelines.
A: The standard covers movement of in-service pipelines, including lateral shifting, vertical lifting or lowering, and angular adjustments. It applies to both buried and aboveground pipelines.
Q: Does API RP 1117 apply to newly constructed pipelines?
A: No. It specifically addresses movement of pipelines that remain in operation. For new construction installations, other standards such as ASME B31.4 or B31.8 and API 1104 apply.
A: No. It specifically addresses movement of pipelines that remain in operation. For new construction installations, other standards such as ASME B31.4 or B31.8 and API 1104 apply.
Q: What is the most critical technical aspect of the standard?
A: Ensuring that combined stresses and strains induced by movement do not exceed allowable limits for the pipeline material and its operating conditions. Proper engineering analysis is the cornerstone of compliance.
A: Ensuring that combined stresses and strains induced by movement do not exceed allowable limits for the pipeline material and its operating conditions. Proper engineering analysis is the cornerstone of compliance.
Q: How does API RP 1117 interact with other pipeline integrity standards?
A: The standard complements other API and ASME standards, providing specific guidance for movement operations that may not be covered in detail elsewhere. It references ASME B31.4, ASME B31.8, API 1102, and NACE standards for coating and cathodic protection.
A: The standard complements other API and ASME standards, providing specific guidance for movement operations that may not be covered in detail elsewhere. It references ASME B31.4, ASME B31.8, API 1102, and NACE standards for coating and cathodic protection.
This article is based on the 2008 (2013) edition. Any updates to the standard should be reviewed for applicability. Always consult the latest official publication of API for definitive requirements.