Case Study: Chemical Plant Safety System Features Advanced Coriolis Meters

Case Study: Chemical Plant Safety System Features Advanced Coriolis Meters
Case Study: Chemical Plant Safety System Features Advanced Coriolis Meters

Global chemical company BASF opted for new Coriolis meter technology as the centerpiece of the safety instrumented system (SIS) of its Freeport, Texas, plant. With its excellent price versus performance, smaller footprint, entrained gas management features, and in situ verification capabilities, the new flowmeter technology improves reliability and decreases downtime for critical process systems.


Plant operators look to replace aging equipment

BASF’s Freeport plant manufactures superabsorbent polymer (SAP), which absorbs and retains large amounts of liquids. The water-absorbing polymer has thousands of uses, ranging from diapers, masking tape, and artificial snow, to hot and cold therapy packs, motionless water beds, and even growin-water toys.

According to Daniel Siddiqui, BASF’s instrumentation and electrical lead engineer for CPN and utilities and infrastructure, plant operators needed to replace flowmeter instrumentation for the SIS, an engineered set of hardware and software controls used on critical process systems. The previous mass meter equipment had reached the end of its lifespan, and BASF wanted to exchange it for newer technology. “BASF’s standards call for replacing SIS equipment at end of life per manufacturers’ recommendation,” said Siddiqui. “The equipment had been showing deviations greater than specifications, and rather than recalibrating it we opted to replace it.”

The plant’s SIS was required to meet safety integrity level (SIL) 3, a measure of system performance and probability of failure for a safety instrumented function, as defined in the IEC 61508 functional safety standards. Among other items, SIL 3 requires a SIS safety instrument with an override for any unusual conditions. Redundant flowmeter instruments are required to alert operators to any flow deviations and trigger a safety alarm. Every time the deviation is greater than 5 percent, the SIS shuts down the production line.

Operators knew selecting the right instrumentation was critical to minimizing any intermittent or false alarm trips that would shut down the production line. Apart from the economic burden from loss of production and wasted material, prematurely stopping under full load (rather than normally ramping down for shutoff) can introduce significant equipment wear and tear.

“The quote we received for replacement meters from the other vendors exceeded our budget; due to the nature of our process, we had to use an exotic material. We reached out to KROHNE, and the quote we got represented significant cost efficiencies compared to the other vendors.” BASF tested the KROHNE meter at its central laboratory in Germany and approved it for SIS service. After reviewing a variety of options, BASF chose a design featuring two KROHNE OPTIMASS 6400 Coriolis twin bent tube mass flowmeters in series to create the required redundancy.

The flowmeters are available in sizes ranging from DN 08 to 250, and can be made in stainless steel 316L, Hastelloy® C22, and Duplex steel UNS S31803. The BASF installation includes two 2-inch meters. The external meter is made of 316 stainless steel, and the internal one is composed of Hastelloy.

Compliant with the User Association of Automation Technology in Process Industries (NAMUR), standard installation lengths are available; the OPTIMASS 6400 operates in high temperatures up to 752°F (400°C), as well as cryogenic applications down to –328°F (–200°C).

It also handles pressures up to 200 bar (2900 psi). It features the new MFC 400 signal converter, which offers fast, completely digital signal processing as well as enhanced diagnostic and status indications.


Price versus performance and entrained gas management

Plant operators reviewing options determined that the price versus performance reliability of the OPTIMASS 6400 was superior to all other options. If operators obtained a reading showing a deviation or another issue with a process monitoring parameter, the meter helped identify the issue in advance, while still performing reliably under the abnormal conditions.

Beyond the purchase price advantage, the OPTIMASS 6400 adds extra value through unique and robust technical features, such as KROHNE’s Entrained Gas Management (EGM) system. Entrained gas can disturb the sensitivity of the mass flow measurement of liquids, decreasing accuracy or even stopping measurement completely. The new Coriolis mass flowmeter technology ensures both stable and uninterrupted measurements with high gas content. The OPTIMASS 6400 provides a reliable indication of gas bubbles in the process by using a combination of various measurements to detect a two-phase flow. With values between zero and 100 percent gas or air content in the line, it maintains the mass flow and density measurements continuously and provides live measured values at all times. At the same time, it can report the two-phase status and output a preconfigured alarm, in accordance with NAMUR NE 107 requirements.

The smaller physical footprint of the meters selected was another benefit, and made installation easier. For example, the KROHNE devices fit into the existing space without major piping modifications, while other vendors’ meters would have required significant piping modifications.

With the OPTIMASS 6400, a proprietary isolation system allows the meters to be close coupled or mounted flange to flange. The unique design ensures that tube vibration has no effect on performance when meters are flange-to-flange mounted. The flow through the meter moves the pipe, causing fluids to swirl, which creates a mechanical distortion between the pipe’s inlet and outlet. The sensor upstream of the oscillator picks up this vibration before the outlet. With other designs, tube vibrations migrate through the piping, causing errors if the meters are close coupled.

In addition, for the same pressure drop, BASF could select a smaller diameter because of the lower pressure drop through the meter compared to other options. This was a real cost advantage to the customer. One other benefit BASF noted was optimizing the stocking of spare parts, ensuring that all meters received have the required entrained gas capability. “We got excellent support from KROHNE and were able to get two meters, which allowed us to stay under our approved budget,” explains BASF’s Daniel Siddiqui.

In situ verification reduces down time due to calibration requirements Safety instrument meters must be verified regularly, and operators are required to establish a proof test interval. Using the OPTICHECK on-site verification tool, BASF can fulfill third-party requirements for independent verification of instruments. The company connects the tool online, while the meter is in service, to verify the flowmeter is performing within ±1 percent of the factory calibration. The baseline can be historic repair data from the factory or on-site test results after performing a full verification. OPTICHECK also has detailed reports for proof test documentation of safety loops.

In situ verification enables the operators to keep the meter operating longer, rather than having to pull the meter out of line, package it, send it off to get calibrated at a predefined interval, and installing it back in service after calibration.

Meter performance since startup Plant operators started up the new Coriolis meter technology for the SIS in February 2020. According to Siddiqui, the system has been operating well, providing accurate readings and offering increased confidence in the SIS application. “With the new equipment, the plant is even safer,” said Siddiqui. “By using the KROHNE meters we did not compromise safety, but at the same time we were able to maximize cost efficiencies, which allowed us to come in under budget. Of the BASF approved vendors, KROHNE’s proposal was the most cost effective, because free startup support was provided.”

This article comes from the January 2021 InTech Focus ebook.

About The Author


Al Dhanji (a.dhanji@krohne.com) is a Houston-based customer representative for KROHNE, Inc. He has account responsibilities for all BASF facilities in the Gulf region.

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