Custody Transfer Calibration: A Faster, Safer, and More Accurate Approach

Custody transfer calibration is a crucial aspect of plant operations, particularly for facilities that handle regulated products. Annual verification is required to ensure that flowmeters used for the sale of commodities remain compliant with state requirements and continue to measure accurately. That accuracy matters because custody transfer measurements determine how much product is legally transferred, billed, and received. For one Interstates client with a facility that handles ammonia, the traditional testing method consumed multiple workdays, required transporting product to a certified scale more than an hour away, introduced fuel-related measurement variability, and delivered limited resolution. When the plant searched for a more efficient and reliable option, Interstates identified an opportunity to bring a proven methodology to a new application—one that set a first-of-its-kind milestone in the state. 

Interstates completed the state’s first custody transfer proving that used a master flowmeter instead of a drive-over certified scale. The team, led by Project Manager Ryan McKnight and Service Technician Cody Petersen, delivered a solution that condensed a multi-day testing process into a four- to five-hour on-site procedure. Their work not only increased efficiency and accuracy but also positioned Interstates as a preferred partner for future custody transfer opportunities across the region. 

Identifying an Opportunity for Improvement 

The facility’s annual testing required filling a transport truck with ammonia, driving more than an hour to the nearest certified scale, recording net product weight after burning fuel during transit, and returning to repeat the process for each meter. This cumbersome approach was time-consuming and resulted in unavoidable measurement inconsistencies. Scales typically round to increments of 20–50 pounds, while fuel consumption during travel introduces additional variability that cannot be corrected precisely. 

Interstates recognized an opportunity to streamline the process. The team proposed using a state-certified master flowmeter and a closed-loop recirculation setup that returns the ammonia directly to the plant’s storage tanks. This eliminated the need for trucking and scale use altogether. The method has been used for other products in multiple states, but this was the first application for ammonia in this state. 

Because the flowmeter is accurate to better than 0.1% of rate, this approach provided a significant improvement over both the resolution and reliability of the prior proving method. 

Ammonia presents unique challenges for flow testing because it boils at –28°F. During initial test runs, the product shifted between gas and liquid states, creating unstable conditions during calibration. To address this, the Interstates team completed an extended “wet-down” the evening before the official test. This cooled all lines and hoses to temperature, kept the ammonia in a liquid state, and reduced the potential for vapor pockets. 

McKnight and Petersen arrived on-site early, performed multiple practice runs, and refined the setup to mitigate phase-change impacts. They also researched the facility’s flowmeters, which are less common in this type of plant, to ensure adjustments could be made efficiently if required. By the time state officials arrived, the system had been tested, stabilized, and prepared for immediate proving. 

Maintaining consistent timing between runs was another critical factor. Keeping the system cold ensured repeatable conditions and reduced the likelihood of variations during calibration sequences. 

Delivering an Efficient, Accurate, and Safe Proving Process 

When testing began, the preparation paid off. The team was able to zero the master meter on the new product, make minor adjustments, and move efficiently between each load-out meter. No significant configuration changes were required because the meters maintained strong accuracy from factory calibration. The two-person team coordinated closely on flow control, data capture, and calibration skid operation, ensuring a smooth and predictable workflow. 

The final results were clear. (A more detailed breakdown of the setup, providing methodology, and calibration process is available in our Custody Transfer Flowmeter Calibration Case Study.) 

• All meters were verified efficiently and accurately.
• The work was completed in approximately four hours.
• No transport trucks or certified driving scales were required.
• The client and state officials expressed strong confidence in the accuracy and speed of the process. 

For the client, this meant fewer operational disruptions, reduced labor requirements, enhanced safety, and more precise measurement results. For Interstates, it demonstrated the value of preparation, specialized technical knowledge, and the ability to adapt proven methodologies to new applications. 

Strengthening Industry Confidence in an Innovative Method 

The success of this project drew attention from both Interstates’ client and state officials. The state indicated it plans to recommend this proving method for other plants, recognizing the time savings, improved accuracy, and safety advantages. The client also expressed interest in applying this approach across its other facilities nationwide. 

This project reinforced Interstates’ role as an innovative partner capable of optimizing processes that have historically consumed significant time and resources. By leveraging the master flowmeter configuration and adapting it to ammonia, Interstates provided a solution that aligns with regulatory requirements while offering measurable operational improvements. 

Accurate custody transfer measurement is crucial for ensuring legal accountability, revenue assurance, and maintaining transparent commercial relationships. For products like ammonia, this accuracy is critical to ensure both parties receive and pay for the correct quantity. 

Through early planning, thorough research, and collaborative execution, Interstates delivered an approach that improves reliability, reduces operational burden, and sets a new standard for custody transfer calibration in the region. This successful proving not only streamlined annual compliance for the facility but also created a repeatable model that other plants can adopt. The experience also highlighted a key lesson for similar projects: thorough pre-planning and conducting practice runs in new applications can significantly reduce risks and ensure smoother execution. Interstates now stands as the first and only provider in the state to implement this calibration method, positioning us for expanded opportunities and continued industry leadership.