Reinventing reliability through material science

Reliability key

Jussi Hellman, Manager of Materials Engineering, is an expert in material science. Initially, he started his career in science, heading a group of scientists at Aalto University that was researching wear resistant materials for various applications (mining, etc.). Since 2002, he has been working for multiple departments within Metso, eventually moving Neles, now Valmet Flow Control business line. “Reliability is very much a call for material science”. Mr. Hellman says. “Needless to say, safety comes first, but the next important feature of an industrial flow control solution is reliability. This parameter allows for an uninterrupted production without malfunctions or failures.”

Needless to say, safety comes first, but the next important feature of an industrial flow control solution is reliability.

More times than often, material wear is the root cause of these failures, which leads to unplanned downtimes and production loss. Additionally, these failures have additional drawbacks, such as material and energy consumption (production and transport of spare parts, ed.) that could have been avoided. Furthermore, the poor performance of flow control equipment often means an increase in fugitive emissions and increased occupational health hazards during production and maintenance, especially if predictive planning and preparation are not possible.

Metal matrix composites

Ceramic materials traditionally play a crucial role in wear protection, Mr. Hellman states. “Various ceramic materials have long been used as a protective lining inside valves, and in many challenging wear applications, ceramic valves offer the best performance available. However, monolithic ceramics have their inherent limitations, such as hydrothermal degradation, limited resistance to thermal shocks, and lack of electrical conductivity. Metal matrix composite materials (MMC) bundle the superior hardness of ceramics and the toughness of metals to offer the best possible reliability and performance to end-users. In MMC, the ceramic addition is embedded into metal, and contributes especially the wear resistance, while the metal carries the mechanical load and improves impact resistance.

Challenging

Valmet has expertise in technologies, such as advanced powder metallurgy which are needed to integrate metal matrix composite (MMC) materials into products. These MMC’s are then used as an inner layer in multi-material constructions where the outer layer is a standardized construction material. This combination is necessary because valves are pressure equipment, and pressure retaining parts must be ductile to meet PED-requirements.

“One typical challenge for the engineering process is that both metals and MMC’s react differently in terms of thermal expansion”, Mr. Hellman says. “This phenomenon can lead to too high internal stresses unless the materials are carefully matched. We have developed several MMC-grades that have been optimized both for manufacturing and operational functionalities.”

Common issue

Coming back to the subject of wear and corrosion, Mr. Hellman says that it is a common issue in various industry sectors. “Although the products from pulp and paper- or oil and gas industry are very different from those of mining and metal refining industries, production facilities struggle with similar challenges in finding efficient protection against severe wear and corrosion.”

According to Mr. Hellman, it is crucial to detect early signs of wear in valves to address this issue pro-actively. And, in terms of process conditions, there are several good risk indicators: high-pressure temperatures cycling (fluctuations), high-cycle operation, sliding contacts, or high noise. Needless to say, the wear issues are more likely to arise in the case of corrosive media, solids in media, or when polymerization or crystallization occurs in the medium.

Wear risk indicators in valves

• High pressure
• High pressure difference
• High/low temperature
• High-cycle operation
• Sliding contacts
• Noise over 85dB
• Corrosive medium
• Solids in medium
• Polymerizing medium
• Crystallizing medium

TCO

Valmet has implemented various MMC based solutions in the field for more than ten years. One example of very successful implementation was at a Fluid Catalytic Cracking unit at an oil refinery. The original CrMo material used for handling catalytic fines (at above 200 degrees C.) failed in between one and three months in operation. The MMC-solution of Neles – in this case, a 5-15 mm MMC armoring onto wear intensive surfaces has extended the lifetime from three to 25 months. “An inspection after six months showed that the MMC did not experience any changes in dimensions. Furthermore, maintenance and HSE-activities were reduced by 90 percent. In other words, MMC’s should be rated in terms of TCO as the investment cost is only one side of the medal.”

Mr. Hellman states that a total prevention/elimination of wear is not always possible. Hence, it is often helpful to balance the objectives and risks using the concept of tolerable wear. “There are various parameters that determine the tolerable wear rate (in mm per year): the targeted remaining useful life (RUL) of the system, the complexity and cost of system repair or replacement, consequences and costs of interruptions in uptime and the safety margin for the occasional acceleration of wear. For each case, the process owner needs to calculate what is the best solution at that time.”

Text by Lucien Joppen, Editor in chief Valve World. 

This article was originally published in Valve World magazine, July 2021 issue.

Text originally published in 2021, and slightly updated in April 2022, due to the company name change to Valmet.