How Can Petrochemical Operators Maintain the Integrity of Their Equipment?

The Challenge

Ģ��tv was asked by our client to help determine why their heat exchanger ruptured so catastrophically, releasing the flammables involved in the explosion.

The subsequent fire burned for several hours, causing secondary damage to the failed sections of the heat exchanger and surrounding piping and pressure vessels. Damage due to high temperatures from flame exposure on these structures can include weakening of the metal, changes to the grain structure, corrosion, cracking, and distortion due to unequal heat stress. This greatly complicated Ģ��tv's investigation, as the secondary damage obscured preexisting damage to the heat exchanger, the source of the initial failure. Given the post-fire conditions, certain possible damage mechanisms were much more challenging to diagnose, like high-temperature hydrogen attack (HTHA), which can leave microscopic traces that may only be present in small, localized areas of the equipment.

The equipment's susceptibility to damage mechanisms that occurred under the observed operating conditions was influenced by several variables, including its materials of construction, process fluid composition and flow rates, and pressure and temperature.

Ģ��tv's multidisciplinary Solution

Leveraging expertise in thermal sciences and materials and corrosion engineering, Ģ��tv's multidisciplinary team performed an in-depth origin and cause investigation, metallurgical characterization of the failed heat exchanger, and heat transfer analysis to determine the root cause of the deadly explosion.

Our thermal sciences engineers documented the accident scene and identified key pieces from the failed equipment to preserve for future analysis. Our experts evaluated the process conditions in the weeks leading up to the explosion by evaluating the heat exchanger's process chemistry, pressure, temperature, and flow measurements, all of which were stored in the refinery's distributed control system. We also created a heat transfer model to evaluate temperature excursions within the failed equipment. Ģ��tv engineers certified in evaluating damage mechanisms pursuant to American Petroleum Institute (API) guidelines conducted a damage mechanisms review to better understand why the heat exchanger failed.
Ģ��tv's metallurgical engineers assessed the heat exchanger's materials of construction to support damage mechanisms review and confirm whether the causes of failure predicted by the review were consistent with the observed damage. A parallel heat exchanger, which was exposed to similar process conditions but did not fail, was also examined to understand whether similar damage existed within adjacent equipment.
Our integrated analysis demonstrated that the catastrophic failure occurred due to HTHA. This occurs when carbon steel equipment is exposed to hydrogen at high temperatures and pressures, causing fissures and cracks that severely degrade the mechanical properties of the steel.

Ģ��tv's Impact

With Ģ��tv's assistance, our client determined the root cause of the heat exchanger rupture. Our findings have since supported the refinery in making changes to their equipment that helped prevent recurrences and contributed to safer processes for the petrochemical industry.

To maintain the integrity of equipment in high-temperature hydrogen service, the petrochemical industry had previously utilized the Nelson curve, which predicts the occurrence of HTHA as a function of temperature and hydrogen partial pressure; however, our investigation, as well as investigations by other independent organizations, confirmed that predictions from the Nelson curve were not sufficiently conservative to prevent all HTHA equipment failures.

Ģ��tv's careful damage mechanisms review provided a solid foundation for our client, enabling them to establish a more effective inspection strategy and mechanical integrity program, supporting them in identifying and predicting HTHA damage, and ensuring mechanical integrity. Our team also advised our client on opportunities to create a safer equipment design by using HTHA-resistant cladding materials.

Case study

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