Subsea Pipeline Integrity and Risk Management

Yong Bai,Qiang Bai

• Publisher: Gulf Professional Publishing
• Year: 2014
• ISBN:
  9780123946485
• Topic: Commerce
• Subtopic: Assurance

Subsea repairs and inspection are costly for petroleum and pipeline engineers and proper training is needed to focus on ensuring system strength and integrity. Subsea Pipeline Integrity and Risk Management is the perfect companion for new engineers who need to be aware of the state-of-the-art techniques. This handbook offers a "hands-on" problem-solving approach to integrity management, leak detection, and reliability applications such as risk analysis.

Wide-ranging and easy-to-use, the book is packed with data tables, illustrations, and calculations, with a focus on pipeline corrosion, flexible pipes, and subsea repair. Reliability-based models also provide a decision making tool for day-to-day use. Subsea Pipeline Integrity and Risk Management gives the engineer the power and knowledge to protect offshore pipeline investments safely and effectively.

• Includes material selection for linepipe, especially selection of standard carbon steel linepipe
• Covers assessment of various types of corrosion processes and definition of anti-corrosion design against internal as well as external corrosion
• Gives process and flow assurance for pipeline systems including pipeline integrity management

Part 1

Pipeline Integrity Management

Outline

Chapter 1. Corrosion and Corroded Pipelines

Chapter 2. Buckling and Collapse of Corroded Pipes

Chapter 3. Dented Pipelines

Chapter 4. Pipeline Inspection and Subsea Repair

Chapter 5. Integrity Management of Flexible Pipes

Chapter 6. Leak Detection Systems

Chapter 7. Fiber Optic Monitoring System

Chapter 1

Corrosion and Corroded Pipelines

Abstract

Corrosion depends on a given environment and the metal type. The presence of carbon dioxide (CO₂), hydrogen-sulphide (H₂S) and free water in the production fluid can cause severe corrosion problems in oil and gas pipelines. Two types of corrosions may occur in the oil and gas pipeline system when the presence of CO₂ and H₂S in the hydrocarbons fluid: sour corrosion and sweet corrosion. The purpose of this chapter is to develop corrosion defect prediction models and the reliability based design and re-qualification criteria for assessing corroded pipelines. This evaluation focuses on corrosion defect growth; check burst strength; check bending capacity and so on. The corrosion products deposited on the steel surface is related to sufficient protection. In this chapter, corrosion defects inspection, calculating method of corrosion defect growth, corrosion predictions are discussed.

Keywords

Corroded Pipeline; Defect Prediction Model; Reliability Based Design; Re-qualification Criteria; Sour Corrosion; Sweet Corrosion

Contents

1. Introduction

2. Corrosion Defect Prediction

Introduction

Sweet: Carbon Dioxide Corrosion

Sour: Hydrogen Sulfide Corrosion

Inspection for Corrosion Defects

Corrosion Defect Growth

Corrosion Predictions

CO2 Corrosion Models Comparison

Sensitivity Analysis for CO2 Corrosion Calculation

3. Remaining Strength of Corroded Pipe

NG-18 Criterion

B31G Criterion

Maximum Allowable Design Pressure

Maximum Allowable Defect Length and Depth

The Safe Maximum Pressure Level

Evaluation of Existing Criteria

Corrosion Mechanism

Spiral Corrosion

Pits Interaction

Groove Interactions

Corrosion in Welds

Effect of Corrosion Width

References

1. Introduction

In most subsea developments, oil and gas production is transported from the subsea well to a platform in multiphase flow without a separation process. Corrosion represents increasing challenges for the operation of subsea pipelines. Corrosion can be defined as a deterioration of a metal due to chemical or electrochemical reactions between the metal and its environment. The tendency of a metal to corrode depends on a given environment and the metal type.

The presence of carbon dioxide (CO₂), hydrogen-sulfide (H₂S), and free water in the production fluid can cause severe corrosion problems in oil and gas pipelines. Internal corrosion in wells and pipelines is influenced by temperature, CO₂ and H₂S content, water chemistry, flow velocity, oil or water wetting, and the composition and surface condition of the steel. Corrosion-resistant alloys, such as 13% Cr steel and duplex stainless steel, are often used in downhole piping of subsea equations and structures. However, for long-distance pipelines, carbon steel is the only economically feasible alternative and corrosion has to be controlled and the flowline protected from the corrosion both internally and externally.

This chapter develops prediction models of corrosion defects and the reliability based design and requalification criteria for assessing corroded pipelines. This evaluation focuses on the following interrelated issues:

• Corrosion defect growth.

• Checking burst strength (allowable versus maximum internal service pressure).

• Checking bending capacity (allowable versus maximum external service pressure, bending moment, and axial load).

• Checking adequacy of residual corrosion allowance for remaining service life.

• Inspecting corrosion defects.

• Updated inspection and maintenance programs.

2. Corrosion Defect Prediction

Introduction

Two types of corrosions may occur in the oil and gas pipeline system when CO₂ and H₂S are present in the hydrocarbons fluid: sour corrosion and sweet corrosion. Sweet corrosion occurs in systems containing only carbon dioxide or a trace of hydrogen sulfide (H₂S partial pressure < 0.05 psi). Sour corrosion occurs in systems containing hydrogen sulfide above a partial pressure of 0.05 psia (0.34 kPa) and carbon dioxide.

When corrosion products are not deposited on the steel surface, very high corrosion rates of several millimeters per year (mm/yr) can occur. This “worst case” corrosion is the easiest type to study and reproduce in the laboratory. When CO₂ dominates the corrosivity, the corrosion rate can be reduced substantially under conditions where iron carbonate can precipitate on th...