1

Phase Chemistry and Corrosion in Subsea

Pipelines

Clare Schoene, PhD SPT Group

Pat McKenzie AQSim

2

Agenda

• Background

– Corrosion in operations

– Production management systems

• Developement

– OLI & AQSim development

– SPT development

• Final Product

– User Interface

– Operations and use

– Simulation advancements

3

Corrosion in operations

• Operational implications of

corrosion

– Safety issues

– Reduced operational lifespan

• Current corrosion management

strategies

– Design

– Operational mitigation strategies

– Field testing – smart pigging

• Little corrosion data available in the

field

4

Production Management Systems

• Manage production and flow assurance issues during operations

– Hydrates, liquids, slugging, pigging

– Virtual metering for phase rate calculations

– Leak and restriction detection

• Utilize field measurements and flow models to predict quantities that cannot be

measured

– Pressure, temperature, composition, phase rates throughout pipeline

– Hydrate formation temperature, dead oil volumes, pig arrival times

• Provide operation information for operations and production engineers

– Alerts and status lights for potential problems

– Forecasting

• Look-Ahead – predicts future issues with current operating state

• What-If – predicts system behavior resulting from a user specified change in operating state

5

Project Description

• Incorporate corrosion analysis into a production management system

– goal of providing

• Level 1: basic operational corrosion information

• Level 2: in depth, on demand, corrosion analysis when necessary

• PMS designed and built for an offshore trunk line network feeding a liquefied

natural gas facility

• PMS provided by GL Noble Denton and SPT Group

– OLI Engine, Advanced Corrosion, is incorporated into the SPT Group portion of the

PMS

– AQSim expertise providing

• Initial corrosion studies for all segments of the pipeline

• Troubleshooting and usage guidelines

6

Data Flow

• Multiphase flow model provides operating conditions in the pipeline for corrosion

calculations

OLI Engine

Advanced

Corrosion

Level 1 Data

Continuous

Level 2 Data

On Demand

Multiphase

Flow Data

User

Interface

PMS

7

OLI Development

• Added multi-phase flow model to the OLI corrosion module

– Designed to receive shear stress from the SPT multiphase flow model

• Expanded the OLI Engine Developer Edition (OLI API)

– Added corrosion simulation capabilities

– Added stability diagrams and polarization curves as graphical returns in the API

– Phase chemistry made available across the interface

8

AQSim Development

• Scenario testing of all segments of the pipeline

• Level 1 and Level 2 troubleshooting guides

– Based on client production configuration

• Guide to “what-if” questions

• Pure H2O versus Produced water substitution

• AQSim project management for OLI / AQSim participation

9

SPT Development

• Level 1

– Develop wrapper to pass inputs and receive Level 1 data from OLI API

– Build corrosion rate profiles from point data provided by OLI API

– Buffer data so the whole profile is complete before data is displayed

• Level 2

– Develop custom graphical user interface for user set up of Level 2 engineering

calculation

– Send Level 2 calculation flag and specified conditions

– Develop a wrapper to pass inputs and receive Level 2 data from OLI API

10

Level 1 Data Presentation

• Level 1 data on PMS screens

– Corrosion rate profile

– Maximum corrosion rate and location

– Corrosion status alerts

• Profile

• Pipeline

• Overall

– Cumulative corrosion profile

– Maximum cumulative corrosion and location

11

Level 1 Screen

12

Level 2 User Input and Data Presentation

• Level 2 User Input Screen

– User selects pipeline and section for in depth corrosion analysis

• Flowline data auto populates if user selects a flowline and section

• Option for manual entry is available

– User can configure water composition data

• Produced water sample or manual entry

– User can configure gas composition data

• Level 2 Data Presentation

– Speciation report, including produced water sample data used in calculation

– Pourbaix diagram

– Polarization plot

13

A Case Study

• Typical but not representative (respecting client privacy)

• Monitoring of corrosion rates indicates a few corrosion hotspots within a flowline

• Utilize Level 2 analysis to gain more data on nature of corrosion in problem areas

and any possible mitigation strategies

14

Level 2 User Input Screen

3 Input Tabs

15

Level 2 Results – Case Study

16

Level 2 Results – Case Study Continued

17

Hypothetical example: Accumulation of corrosion rates at a single point

18

Technology Incorporated

• SPT Technology

– OLGA - transient multiphase flow model

– Composition tracking module

– Corrosion advisor

• corrosion rate alarms

• cumulative corrosion

• OLI

– Modify OLI API to accept shear-stress data

– Handshake interface files between OLGA and OLI Engine

– OLI Flash calculation

– OLI Corrosion calculation

– Multi-phase flow effects on corrosion

• Potential problems

– Different phase predictions between OLGA and OLI Engine

19

How this moves the industry forward

• Transient flow with electrolyte thermodynamics

– Scale prediction vs. time

– Corrosion prediction vs. time and length

– Slugging locations saturate gas with liquid components, so composition is no longer

constant nor trending evenly

• Multi-phase effects on corrosion

– Gas-water and Oil-water ratios are now included

20

Summary

• An approach to monitoring and managing corrosion during operations is presented

– Provides operational corrosion rates and cumulative corrosion rates along the length of

the pipeline

– Operational alerts are available based on user specified corrosion rate limits

– Ability to perform on demand, in depth corrosion analysis at locations of interest along

the pipeline

• AQSim and SPT development of a custom software interface and user interface

allowed the inclusion of rigorous corrosion calculations based on conditions in the

pipeline

21