In September 2021, our team faced a critical challenge while working on an oil separation vessel project for KNM Process System in Malaysia, developed by SBM Offshore. Despite adhering to industrial standards such as ASME and API, the vessel exhibited a defect at the head-to-shell joint, causing an inward bend near the edge. Left unaddressed, this defect could have resulted in catastrophic accidents or even loss of life. Our mission was to determine whether the vessel could be safely utilized under its intended design conditions.
Fig. misalignment overview.
Fig. actual onsite view.
Challenges
Upon delivery to SBM Offshore, a misalignment was discovered in the vessel, even though it complied with ASME regulations. This misalignment fell short of ASME VIII standards, posing a significant risk of financial loss and project delays for both the manufacturer and the client. To mitigate these risks, the vessel had to meet the stringent requirements of ASME VIII DIV-2-2019 Clause 6.1.6. This is where Ideametrics stepped in to find a solution.
One of the primary challenges was to accurately model and replicate the dent in SolidWorks using six offset points provided by the client.
Fig. detailed view of 12 mm offset
The above image highlights the real-world misalignment caused during manufacturing. The bent cross-section measured 300 mm, with six data points capturing the misalignment. The inward bend was on the head side, where the weld offset varied between 7 mm and 12 mm, with a total weld length of 300 mm.
Solution
To facilitate weld compatibility, we tapered the shell’s exterior by 2 mm and the head’s interior by 5 mm. These modifications allowed for easier weld fitment. The vessel was constructed from stainless steel and designed to handle a working pressure of 6 MPa and a temperature of approximately 125°C. Due to these high operating parameters, validating the vessel’s design according to ASME standards was imperative.
Using ANSYS, we modeled the vessel, meshed the body, set boundary conditions, applied internal pressure inputs, and conducted a thorough stress analysis. Accurate stress calculations were key to evaluating whether the design was safe and effective.
Results
The final analysis confirmed success. Key results included:
- Maximum Stress at the Misalignment Region: 477.19 MPa
- First Load Condition:
- Primary Stress: 280.03 MPa
- Allowable Stress: 381 MPa
- Second Load Condition:
- Combined Primary and Secondary Stress: 470.18 MPa
- Allowable Stress: 762 MPa
These results validated that the design met all safety and performance requirements, saving both the client and manufacturer significant time, effort, and costs. The client expressed satisfaction with the solution, having avoided unnecessary expenses and delays.
Iteration Process
Our design validation process involved three key iterations:
- First Iteration:
We received six random offset points and modeled the maximum offset at the center, with others arranged in descending order. The analysis was conducted accordingly. - Second Iteration:
We received exact offset point locations and re-ran the analysis with all offsets positioned externally. - Third Iteration:
Information about an internal bend surfaced, prompting us to adjust the analysis for greater accuracy.
Final Thoughts
In today’s fast-paced industrial landscape, precise simulations and robust design validation are crucial for ensuring optimal performance and safety. Addressing manufacturing defects through rigorous analysis grounded in standards like ASME and API not only guarantees reliability but also minimizes risks. The KNM oil separation vessel project showcased how reverse engineering and simulation can bridge the gap between design flaws and safe, efficient operation.