Hazardous Process Gets Important Improvement

Sept. 10, 2019
New safety instrumented system reduces risk and eases future expansion

With a production history that dates back to 1899, PPG’s plant in Barberton, Ohio, is no stranger to change. Its products have evolved from raw materials for glass-making to today’s range of specialty chemicals. The site’s operations also have completely transformed from manual processes to more-automated ones tied into a distributed control system (DCS).

One of the most recent changes in the plant was in how workers evaluate and mitigate safety risks. In 2016, the company adopted the layers of protection analysis (LOPA) risk-assessment method to give workers a better understanding of the effectiveness of plant safeguards. The methodology also has proven useful in identifying areas where the site can further strengthen those safeguards.

Safety Risks Uncovered

The chloroformate unit is one of the Barberton plant’s smallest process units but one of its highest safety risks.

Workers at the plant have performed process hazard assessments (PHAs) on the unit for decades in accordance with the U.S. Occupational Safety and Health Administration’s Process Safety Management Standard (29CFR1910.119). With the adoption of LOPA, workers had to evaluate the safeguards identified in those PHAs to quantify and validate their effectiveness.

For example, LOPA helped workers pinpoint scenarios with the highest risk. These scenarios required redundant pressure transmitters for one of the inputs to meet the safety integrity level (SIL) rating.

“We started by evaluating our current interlocks and looking at the scenarios they might be protecting,” notes Matt Kinsinger, senior process control engineer, PPG Industries. “Then we re-evaluated anything that we had already ranked as a high risk in the PHAs to make sure it had adequate protection. This helped us identify opportunities where the existing control system, instruments and control devices could be improved to meet our acceptable risk level.”

Next, Kinsinger and his team developed requirements for a new safety instrumented system (SIS) in accordance with the ISA-84/IEC-61511 standard. The new SIS would need to not only help reduce risk on the process unit but also address other key plant requirements, including:

• Usability. The SIS should provide an easy-to-use operator interface easily integrated with existing DCS interfaces.
• Scalability. It should support new or modified plant equipment.
• Expandability. The system should readily accommodate expansion or additional requirements for higher levels of protection based on future analysis or PHAs.

Making A Choice

The team reviewed SIS offerings from two vendors whose technologies were already used in the plant. It wound up selecting the AADvance system from Rockwell Automation in the spring of 2017. This flexible and scalable system suits operations ranging from those with a small number of inputs and outputs (I/Os) to large systems, and can meet multiple SIL levels in an application. It also provides easy, standard communication to the plant’s existing Allen-Bradley ControlLogix controller.

“The AADvance system hit all our boxes for an SIS,” Kinsinger says. “The price was great. It met our initial requirements. And it could easily be expanded or scaled-up, as needed.”

Once the order was placed, the team had a short timeline of four months to develop the new system and implement it during a planned outage.

To start, Rockwell Automation assigned a project manager and project engineer to support the upgrade. The project manager coordinated the team’s meetings, communication and documentation to keep the project moving and verify milestones were met. The project engineer worked directly with Kinsinger and his team to develop a system that met all its needs.

For the factory-acceptance test (FAT), Kinsinger traveled to the Rockwell Automation Houston facility with a spare controller that was modified to include the SIS communication. The Rockwell Automation team performed a detailed FAT, including simulating every safety instrumented function (SIF), I/O point, and bypass and reset condition.

The SIS then was shipped to the Barberton plant where PPG personnel performed a site-acceptance test (SAT) without any outside support. This provided a validation of the system as required in the ISA-84/IEC-61511 standard.

Implementation of the system at the plant involved the physical installation of additional valves and relays to be controlled by the SIS. The team also put in a few extra transmitters and rewired some existing field instruments to the SIS instead of the DCS. Planning for the physical installation of the valves and instruments, combined with the piping modifications required, quickly became the most challenging portion of the project, recounts Kinsinger.

Closing The Gap

Kinsinger and his team hit the target of installing the AADvance system and going live according to the scheduled timeline.

The new SIS provides the protection required to meet the plant’s acceptable risk level for the chloroformates process unit. It also offers flexibility to grow or evolve with the plant. This is important because the process already is at capacity and probably will need expansion. Also, continual re-evaluation of process hazards in the plant means changes to the SIS are very likely.

“We performed what we felt was a comprehensive review of the current system,” Kinsinger explains. “But we also wanted room for any additional items to be added to the SIS or requirements for higher levels of protection based on future PHAs.”

 PETER SKIPP is process safety manager for Rockwell Automation, Houston. Email him at [email protected].

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