TROUBLESHOOTING FOR CRUDE METERING SYSTEMS

Belman Group supplied over 20 Expansion Joints to a refinery in Norway as part of a major upgrade to a process system that had been in operation for decades. These Expansion Joints were specified by the client for use in crude oil metering stations where they served as mount/demount units to allow for the periodic removal and calibration of fiscal flow meters.

CLIENT ISSUE
Rather than using traditional flange-jacking methods, the client’s approach relied on tie rods to retract the Bellows by approximately 25 mm, creating the space needed to remove the flow meters. After calibration, the Bellows were extended back to their original length using the same tie rods, and the line was brought back into service (typically under conditions of around 38°C and 19.6 barg). Over time, however, the Expansion Joints were subjected to thermal and mechanical loads beyond those anticipated in the original design, and after a critical incident occurred, one Expansion Joint failed and several others sustained visible damage. Although the exact cause of the failure could not be definitively determined, the pattern of damage pointed to a potential water hammer event. To safeguard the system’s integrity and guarantee safe operation, Belman Design was brought in to perform a comprehensive technical investigation and develop corrective solutions.

BELMAN DESIGN SOLUTION

3D modelling, inspection and stress analysis of key metering units

The project began with an on-site inspection to assess the condition of the installed Expansion Joints. Using AutoCAD Plant 3D, a detailed 3D model of the affected piping section was developed to accurately reflect the system layout and facilitate further analysis. This model formed the basis for a complete piping stress analysis performed using ROHR2, which included standard operating conditions as well as two additional dynamic load cases simulating a sudden interruption of product flow, used to replicate the effects of a potential pressure surge or water hammer.

Contributing factors to the Expansion Joint failure:

• Overloading of components: Significant damage was observed in the lugs and tie rods of the Expansion Joints, which were exposed to loads exceeding their original design capacity.
• Pipeline movement: The affected Expansion Joints were connected to a manifold that was free to move, leading to unrestrained motion and higher stress levels on the components.

Based on these findings, a series of targeted technical improvements were proposed:

• New Bellows were designed for critical lines, incorporating allowances for alignments and precise tolerances for build-in lengths.
• A full replacement of all bolting assemblies was recommended, with structural verification to ensure mechanical integrity.
• A revised support strategy was introduced, including simplified bolted supports designed to limit movement and reduce on-site welding requirements.

A cautionary note

Over time, changes in layout, process conditions or support configuration can significantly impact how a pipeline behaves. When replacing Expansion Joints, it is critical to reassess the system with an updated stress analysis, accounting for all realistic operating scenarios.