Mesh network: Each field device acts as a sensor and a relay device, or router, for the radio transmissions creating an interlocking web of sensors
By Dr. Kris Pister and Greg LaFramboise
Chevron refines more than 2 million barrels of oil a day. However, in many respects Chevron considers itself a “technology” company that produces energy.
To Chevron, technology creates opportunity and a sound technology strategy forms the basis for their business planning.
Recent successful testing of wireless sensor networks and subsequent rollout has poised Chevron to generate some of the most substantial gains in productivity to date.
Chevron employs approximately 60,000 people in more than 100 countries. Like many heavy industries, its facilities range in age from those more than 100 years old (Richmond California refinery, 1901) to newly built. Thus, the challenge for Chevron has long been how to improve the performance of each facility regardless of its age and extract maximum productivity from each site, all the while funneling vital information to a central location.
The company’s multi-billion dollar investments in sophisticated equipment for oil fields and offshore rigs provided part of the solution but still required numerous personnel to operate and monitor. Wireless sensors have long been an important part of these investments, but installing wireless sensors is labor intensive and adds significant cost. Chevron had long considered using wireless, but the earliest point-to-point wireless sensors lacked reliability and a unifying standard that would allow multiple vendor interoperability.
However, a lot changed in wireless sensor technology in a few short years, and today the potential for standards-based wireless field devices in Chevron’s operations represents a large opportunity.
The promise of wireless
For Chevron, a wireless sensor network had to address a number of key factors. These include:
Monitoring rotating equipment such as pumps, including those in remote oil fields
The extraction of more sophisticated information regarding device diagnostics and preventative maintenance data, believed to be “stranded” in the devices and inaccessible to the existing control system
The addition of equipment not previously monitored due to the limitations of installing wired infrastructure
The testing of new applications including the extension of the process control network to mobile operators
Locations for the initial test included onshore petroleum producing fields located in California and Texas. These facilities used wireless sensors in various applications from monitoring process equipment within facilities to monitoring large sections of producing property with clusters of instruments over hundreds of feet.
In the San Joaquin Valley, deployment of sensors provided information for process and equipment optimization. This location also included mobile worker applications to provide operator access to data from their service trucks, greatly increasing productivity of the production personnel. Similar mobile worker applications deployed in the Gulf of Mexico on offshore production facilities.
At Chevron’s Richmond facility, wireless equipment went to work to monitor process data from pumps and bring the data back to a unit control room.
An open pit coalmine in Kemmerer, Wyo., also gained wireless intelligence with the monitoring of crushing and conveying equipment, the movement and monitoring of coal trucks, and even the monitoring for clogging of the coal dump “grizzlies” (grates used to catch over-sized pieces).
In one oil field, a central oil well had to drill down on a cleared site within a forest of vegetation. The soil was very rocky, and this made it difficult to install conduit below grade. Installing the conduit above ground was undesirable since it would restrict servicing equipment access to the wellhead.
In addition, the associated processing equipment was located at the edge of the well pad to maintain clearance. A wireless sensor network was installed to provide complete sensor connectivity between the well and equipment.
Mesh wrap around transmission
The harsh environments at industrial locations such as a remote oil field or a refinery are notoriously hostile to radio frequency (RF) signals. The use of concrete, steel, and glass in the construction of typical plants exacerbate the traditional RF issues of path loss, fading, and multipath signal interference.
To solve this problem, Chevron deployed a type of wireless network called a “mesh” network where each field device acts as both a sensor and a relay device (or router) for the radio transmissions, creating an interlocking web of sensors. This requires minimal power because the data radio transmission travels just a short distance to reach nearby nodes, and only needs to communicate for a short period between measurements, allowing sensor batteries to last for an average of five to seven years in the WirelessHART devices deployed.
The wireless sensor network, in turn, communicates with plant’s wired infrastructure, which sends data back to the control room for monitoring and analysis.
What makes mesh network architecture so compelling is its ability to self-organize and self-heal—these attributes minimize maintenance costs and assure the constant flow of information.
If one node goes down, the system simply finds an alternative path for sensor traffic by looking across all available RFs, then enhancing the signal through a spread spectrum coding technique that moves the message from node to node, an approach called “channel hopping.”
Unsurprisingly, security was of paramount importance to Chevron whose facilities are critical infrastructure. To meet and exceed security requirements, the basic building blocks of a secure wireless industrial solution for Chevron’s facilities developed with the following characteristics: confidentiality, data integrity, relay protection, and denial-of-service protection.
Confidentiality was addressed through end-to-end data encryption using a 128-bit Advanced Encryption Standard (the National Security Agency endorses AES for use in protecting systems and secret information critical to national security).
Message integrity codes protected the data integrity of the information transmitted to ensure there is no tampering with the information and it originated from a known source.
In addition, replay protection prevents attacks on both the link layer and the network layer by using non-repeating replay counters as was denial-of-service (DoS) protection although channel-hopping protocol diminishes the risks of a DoS attack by using the entire radio space.
Immediate and term benefits
What made Chevron’s wireless sensor network installation so successful was the immediate cost savings reaped by not having to wire up the sensors with cable and conduit. This can be 75% of the cost of a project.
For the wellhead project, Chevron estimated the wiring costs alone for the dozen sensors installed around the well pad would have been approximately $10,000.
This dramatic reduction of installation costs and complexity meant Chevron staff could focus on the project goals of increasing production efficiency, reducing operational downtime, and above all, making it easier for the operators to monitor and control the production process.
Over the longer term, Chevron believes wireless sensing will play a pivotal role in allowing plant personnel to further optimize the process and respond more quickly to equipment and process malfunctions. Predictive techniques will further optimize preventative maintenance schedules as well, saving technician time.
The successful initial projects have quickly expanded to include the upgrade of hundreds of sensors and the beginning of planning for a much bigger global wireless initiative.
Chevron plans to build out a wireless backbone meant to directly integrate into the process control network and create points of entry for the sensor networks. This will provide a high-speed, reliable wireless backhaul capable of moving the process sensor data from the process units back to the control room, in some cases miles away.
Chevron’s ambitious goal for this portion of the project is to develop a wireless standard for global refining by creating an overarching wireless network, a work already in progress at the first refinery.
While both the backbone and the sensor networks will be wireless, Chevron expects the backbone to have very different characteristics compared to the sensor networks. This is somewhat like a vast, multiple lane freeway, or backbone network, capable of moving people and goods across long distances, while slower surface streets reaching into each individual neighborhood and home represent the sensor networks.
The wireless mesh network for the backbone platforms on IEEE 802.11 technology, a radio standard proven to co-exist with the sensor network’s IEEE 802.15.4 standard.
Chevron’s architecture also includes end-to-end security across both networks and a guarantee of quality of service to ensure critical plant data gets through.
Chevron originally envisioned that the integration of these two networks might include convergence with network access for mobile worker handheld devices, or general-purpose computing devices, conservative planning resulted in a revision to that portion of the project.
Chevron’s preliminary security analysis showed a more detailed assessment was required to address WiFi enabled clients. However, as mobility remains a critical element, security of handheld devices is on the agenda in the projects’ next phase.
As the project to fully integrate wireless technology into its operations progresses, Chevron continues to demonstrate the ingenuity and focus on continuing performance improvement that has long been a hallmark of the firm.
ABOUT THE AUTHORS
Dr. Kris Pister (firstname.lastname@example.org) is a professor of electrical and computer engineering at the University of California, Berkeley. He is a founder of Dust Networks. Greg LaFramboise (email@example.com) is Wireless Technology Lead at Chevron Energy Technology Company in Richmond, Calif. He is the company’s voting member of the ISA100 Wireless Committee.
A primer to industrial wireless-device network success
A network cannot require sophisticated planning or site mapping to achieve reliable communications.
Installers of networked devices should not have to be specialists in wireless; they are more likely to be experts in their own fields.
The protocol running should do all the networking work, leaving the installation engineers to focus on what they know best.
Human intervention should not be necessary for the network to move a packet of data from one end to the other. The network should figure this out by itself. This self-configuring and self-healing aspect is vital for reliability in harsh industrial environments.
Nobody uses wireless for fun. There has to be a pragmatic reason to switch—namely lower cost and ease of installation. If it is not easier and less expensive than copper, then the promise of wireless will never materialize.
A network must be reliable. The network error rate should be below acceptable levels, as defined by the customer. It should be scalable. Device networks of tens of thousands of end points should be possible and should not require detailed network planning.
As to security, when isolated wireless networks tie into existing networks and, ultimately, to the Internet, security is paramount. By linking remote devices to the Internet, they assume the vulnerability of any Internet-enabled structure as they come online.
It is important each device contain the capability to invoke appropriate strengths of encryption for their applications.
Range is important in the context of a typical industrial network. While the span of the entire network often needs to cover several tens of thousands of square feet, the average distance between end points (nodes) is usually only a few tens or hundreds of feet.
Power is not always available at the sensing or control point. Successful industrial wireless devices will often need to run on scavenged power or operate for several years using battery technology.
Successful industrial wireless networks need to coexist with the wired world. It is important they be able to emulate the characteristics of wired networks. A true test of a successful wireless network is one where a user unplugs the wired network from a device and its controllers and plugs in a set of wireless devices.
The network should be able to configure itself and pass data without needing to reengineer the devices themselves.