Sasol accomplished this feat by taking the capabilities of its HART-enabled instrumentation beyond configuration and calibration to develop an alarm system that permits true proactive maintenance. Implementing this program led to additional beneficial results such as reduced start-up costs and fewer programming errors.
Sasol’s move from reactive to proactive maintenance began in 2000 with the development of a strategy for detecting problems in field instruments before they caused production losses. The old maintenance workflow chart is presented in Figure 1. Other benefits would include improved management of change, intangible enhancements in product quality, and reduced instrument maintenance costs.
The plan was to move the butanol and acrylic acid (AAA) plants from a reactive mode of maintenance to a predictive mode. One key problem at these plants was control valve maintenance. To reduce this problem, a program was initiated to develop signatures of all control valves before they left the factory. Once the valves were in use, the signatures could be compared against the baseline to qualitatively isolate faults and identify process issues.
Five years later, the Sasol plan is a success. “We have realized more than $2 million (USD) in documented savings to date and will continue to enhance our use of HART technology,” says Johan Claassen, engineering manager, who has worked with Sasol since 1995. The new workflow chart is presented in Figure 2.
A work in progress
As is often the case with industrial growth, success requires a marriage of managerial minds with engineering skill. For Sasol, the key was the team decision to use HART digital communication technology to maximize the intelligence in their field devices even though Sasol was already invested in another DCS. “We were convinced HART had the best technology for maximizing the intelligence capabilities in our field devices, given our large installed base of HART instruments” says Claassen.
The initial plan was to utilize an OPC protocol to communicate between the DCS system and the Device manager. Communication was balky and slow. The Device manager received diagnostic bits generated by several devices. If an error was detected, a single error bit was set to the DCS via the OPC. This bit was displayed on the operator screens as a flashing blue triangle next to the instrument (Figure 3).
This system was implemented in 2003 when the butanol plant was commissioned. Unfortunately, the OPC approach proved to be unreliable and was ignored by operators. In 2004, it was time for a change. The engineering team took on the task of extending improvements made in the butanol plant to the acrylic acid plant.
An asset management interface was installed to send e-mails to the AMS (asset mangement system) specialist, planners and managers (Figure 4). The perception among operators was still poor because of technical problems. To meet this challenge, additional asset management software was installed in January 2005.
Late in 2004, Sasol integrated the Midland Solvents plants (butanol plant and acrylic acid plant) with the Sasol 1 Solvents and the Germiston Solvents plants. Expanding the plan to encompass these two sites was even more of a challenge.
A different strategy was required for each site because of the difference in age of each system. The Midland site had the newest HART systems; Sasol 1 and the Germiston sites relied on older systems. From 2007, these sites will be incorporated in a general reliability program where diagnostic information is fed to the asset management systems. Sasol’s engineering team is currently busy with a large DCS and instrument upgrade project on the Sasol 1 and Germiston Solvents plants to get the base systems ready for asset management utilizing HART technology.
After five years of work, Sasol’s efforts have produced significant results. The benefits achieved already include:
- prevention of three plant trips ($1.6M savings );
- prevention of problems with several valve positioners and valves ($0.4M);
- improved safety audits, valve signatures, instrument settings;
- quick download of transmitter settings – fewer errors; and
- less reactive, more proactive maintenance.
These accomplishments led to Sasol being selected by the HART Communication Foundation as the 2005 HART Plant of the Year, the only public award presented to end user companies to recognize ingenuity in the application of HART technology.
During the past five years, Sasol engineers have learned several hard lessons, including:
- multiplexer networks require frequent resets;
- reducing the alert time between the device and asset manager is the key;
- all vendor networks are not the same — review qualifications carefully;
- define the fault tree upfront to establish a reliable alert system;
- don’t overload your process operators with these alerts — use maintenance people to monitor alerts;
- the reliability of the systems depends on the I/O system; and
- developing and using a management-of-change program is crucial.
Future plans include upgrading the Sasol 1 Solvents site DCS. “We will make use of the integrated HART I/O to connect to existing HART field devices. We also have a renewal strategy on the older field devices to change them to HART field devices,” says Claassen. On the Germiston site, where the technology is more current, Sasol plans to install asset management systems that will allow the company to reap the benefits from these intelligent field devices.
As for the Midland site, the company plans to link its AMS system to the Sasol 1 SAP maintenance work management system. “The butanol and acrylic acid plants have paved the way for the rest of Sasol’s plants to implement these technologies and start harvesting the benefits of the system,” says Claassen.
“We will remain at the forefront of technology in Sasol Solvents SMG Operations and we will continue to search for technologies that will improve preventative maintenance technologies in the Instrument field. Although we are not first in the world with regards to HART technology, we see ourselves in the top five companies in the world.”