Even small measurement errors during custody transfer can be extremely costly for producers of industrial gases. One such company, dissatisfied with the flow metering system on its fleet of gas transport trucks, approached WIKA for help in coming up with a better product.
Manufacturers of industrial gases typically produce and liquefy the gases – hydrogen, helium, nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, etc. – at their facilities, then deliver the products to businesses that need them. These gases are used as raw material, energy source, feedstock, and more in industrial applications, as well as in medical treatments such as oxygen therapy.
The supply modes range from pipeline distribution to cylinder and bulk delivery via tanker trucks. To know how to charge customers, producers must have a reliable way of measuring the precise volume that is being dispensed. Accurate flow metering is essential in custody transfer. Even small errors in measurement can be costly for suppliers – and sour relations if customers feel they have been shortchanged.
Problem: Low-Accuracy Flow Meters
The Brazil branch of a global industrial-gases supplier was having issues with accurately measuring the flow of nitrogen, oxygen, and argon when releasing the gases from their tanker trucks to customers’ containers. Its flow measurement system was certified for an accuracy of ±2.5%, which turned out to be too low for this particular application.
Customers do have their own system for fiscal metering: weighing the supplier’s tanker truck before and after dispensing to calculate how much product they received. However, the platform scales used to weigh the trucks belong to the customer, and thus are not under the supplier’s control in terms of accuracy and repeatability.
For the Brazilian supplier, its customers’ uncalibrated and possibly inaccurate weight scales led to concerns during the charging process. This uncertainty was compounded by a lack of confidence in the accuracy of its own flow metering system. Since the company has long used WIKA instruments, especially the 732.14 differential pressure gauges for cryogenic applications, its engineering team asked if WIKA Brazil could come up with a better solution.
List of Requirements for a New Flow Measurement Device
The industrial gas producer had a very specific list of requirements for its next flow metering system:
- Accurate – ideally around ±1.0%
- Compact – as it will be installed in transport tank trucks with minimal additional space
- Robust – ability to withstand high vibration for when traveling on unpaved, uneven roads
- Versatile – one device for measuring three different liquefied gases and their process data
- Suitable for cryogenic applications – fluid temperatures as low as −185°C (−301°F)
- Suited for small piping diameter – DN 1½”
Trials, Errors, and Success
At first, WIKA product specialists thought they should go with a cryogenic design for a meter run according to ASME MFC 14M. This solution checked all the boxes… except it wasn’t compact. The final length would have been 2.5m (8.2 ft.), which would not fit the space available in the truck piping system.
They went back to the drawing board. Attempt #2 was the same meter run design but with a multi-hole orifice plate to reduce the length. However, accuracy suffered and did not satisfy the customer‘s requirement of ±1.0% accuracy.
WIKA Brazil was starting to think they couldn’t meet the gas producer’s requirements for both accuracy and compactness when someone on the team remembered a similar situation from a few years ago. WIKA had customized an HHR (high head recovery) FlowPak® assembly for another customer. (The FlowPak® has excellent accuracy, like a meter run, but without the need for straight piping upstream or downstream.) That customer, after receiving the product, decided to change the pipe size from DN 3″ to DN 1½”. Using this case as a reference, the team used a similar model and sized the FlowPak® to DN 2″. With inlet and outlet reductions, they were able to bring the piping diameter down to the required DN 1½”.
At the gas producer’s site, WIKA product specialists tested their FlowPak® flow measurement system by comparing the results to the before and after weights shown on a truck scale.
Finally, Attempt #3 had all the attributes that this customer was looking for:
- Accurate – high accuracy of about ±1.0%
- Compact – only 600mm (23.6 in.) long
- Robust – no moving parts
- Versatile – able to handle liquid nitrogen, argon, and oxygen with stable differential pressure, and well as their process data
- Suitable for cryogenic applications – grade AISI 304/304L stainless steel, all-welded to prevent leakage
- Suited for small piping diameter – DN 1½”
When the product specialists tested their innovative flow metering device against the customer’s current system, WIKA’s solution outperformed it with less permanent pressure loss. The gas company’s engineering team was happy with the solution… except for one final sticking point.
Additional Challenge: Lowering the Cost while Maintaining Quality
The customer has hundreds of tanker trucks – enough to service all corners of the world’s fifth largest country – for different industrial gases, and each truck required the improved flow meter. Thus, even a small reduction in the per-unit cost would help the company stay within budget. The engineering team asked if it was possible to bring down the price.
WIKA Brazil accepted the challenge and immediately got to work. After looking for places to trim cost, the product specialists decided to revamp the fabrication process. In the previous attempts, they bored a hole through a round metal bar for the entry cylinder, located upstream of the FlowPak®’s throat. To save on labor and material costs, they changed that part to a piping tube.
Rounding out the flow metering assembly are a temperature-compensated differential pressure transmitter and Pt100 temperature sensor for inferred mass flow measurement.
The customer was delighted with Attempt #4; the WIKA-designed flow measurement solution met all the technical requirement and was affordable. Six months after the gas company’s engineers started collaborating with WIKA Brazil on this project, they ordered 150 units of the FLC-HHR FlowPak® and the TR40 cable resistance thermometer (2 x Pt100 4-wire) to be installed on their oxygen tanker trucks, with future plans for the same system in trucks transporting nitrogen and argon.
WIKA, Partners in Problem Solving
The flow specialists at WIKA enjoy a good challenge and love collaborating with customers to innovate measurement solutions that are accurate and robust yet cost-effective. Contact us for more information about how WIKA products can help improve your business’s efficiency and bottom line.
Products mentioned in this article
• FLC-HHR-FP FlowPak® flow meter
• TR40 cable resistance thermometer
[contact-form-7 id=”14552″ title=”Blog Contact Form”]