Message-Based Communications for Pipeline SCADA

Stephen Koenig, P.E.

Smarter Infrastructure for Oil and Gas

December 3, 2013Houston, TX

source: http://www.epa.gov/gasstar/images/newsroom/fall11-valve.jpg

source: http://www.welkereng.com/wfms/portfolio/images/pipeline.jpg

source: http://www.transport4.com/PublicSite/t4publicweb/home.aspx

Data stored in the meter station Flow Computer

Sensor Data

Data stored in the Corporate Accounting System

Data calculatedby meter stationFlow Computer

Messaging - Basic Concepts

• Multiple data sources (publishers) send messages to multiple data destinations (subscribers)

• Destinations subscribe by “topic”

• Payload can be anything: text, binary, fixed fields, etc up to 250Mbytes in size

• Broker supports multiple delivery options (QoS)

Data Destination

Data Destination

Data Destination

Data Source

Data Source

Data Source

Network

Message Broker

Data Source

Data Destination

Publish Subscribe

Message Format

Topic Payload

Automation to SupportPipeline Operations

F

TP

FlowComputer

RemoteTerminal

Unit

CommProcessor

TankGaugingSystem

SatelliteLink to ControlCenter

source: http://www.northerngateway.ca/assets/498x245_contentimages/EnvironmenatlResponsibility/Pipelineassesment.jpg

source: API RP 1165 – Recommended Practice for SCADA Displays

Traditional Approach to SCADA Poll/Response

• Host & RTU’s are serial devices – typically Programmable Logic Controllers

• “Round Robin” polling

• Data format optimized for mininimum overhead

Problems with Poll/Response systems

• Host “owns” communications link

• Dedicated circuits are too expensive

• Alarm latency increases with RTU count

Evolution to Message-Based CommunicationsStep 1

Evolution to Message-Based Communications Step 2

Evolution to Message-Based Communications Step 3

Evolution to Message-Based Communications Step 4

Challenges in Use of Message-BasedCommunications for SCADA

• Controls – limited life in system• Stale Data – replace poll/response

functionality in event-driven system• Security

– Flexible architecture may result in new vulnerabilities

– Message-based system must be as secure as traditional poll/response

– Need for continuous improvement

Benefits of Message-Based Approach to SCADA

• Topic/Payload Message Structure• IP Routing• Intelligent Front-End Processor• Many-to-Many Architecture

Benefits - Topic/Payload Message Structure

• “Wildcard” subscriptions

•Support for multiple applications on one message broker

• Use of version number in topic

- Facilitate prototype and test of new clients

- Allows site-by-site migration strategy

Benefits – IP RoutingScalability

Benefits – IP Routing -- Redundancy Reducing the Impact of Failure

• Provisions for broker equipment failure

• Provisions for loss of primary communications link – backup link

Broker1Broker2Broker3Broker4

Benefits – Intelligent Front-End Processor

• Adapt Serial Devices to IP/VSAT

• Move polling/response to field

• Ability to handle multiple RTU protocols

• Local intelligence can supplement or enhance control system

Broker1Broker2Broker3Broker4

Benefits – Many-to-Many Architecture

• Significantly reduced project schedules

• Off-line systems receive live data for testing

Future Opportunities for Message-Based SCADA Systems

(from a 2005 perspective)

• “Flight Simulator” for pipeline Controllers• Interface to business systems• Real-time meter ticket transactions to

shippers and other carriers’ business systems

• Distributed SCADA