[ Duplex ]
[ Duplex ]
Figure 2 . Carbon footprint ( CO2e ) comparison of various materials based on both PCF ( ISO 14067 ) and EPD .
Nickel alloys require more virgin alloying elements to obtain the right composition and quality so the carbon footprint soars with increasing nickel content . Consequently nickel suppliers with the strongest focus on reducing their emissions should be awarded . Only a couple of EPDs have so far been identified for nickel alloys 17 . It is the same situation for titanium alloys , with few EPDs found . Titanium production relies largely on the energy-intensive sponge process . The available EPD is from Japan and the declared CO2e value is significantly lower for the ‘ green ’ product where more than 50 % scrap is used 18 compared to an unknown scrap ratio in the regular version from the same supplier 19 . Fiber reinforced plastics ( CO2 from partial LCA ) - Finally , ( glass ) fiber reinforced plastics ( FRPs ) are growing as an alternative material for chemical industry process equipment . EPDs for FRPs as such has not been found . However , by using a trusted database , the carbon footprint of its constituents ( 60 % E-glass , vinylester resin ) can be found and based on that , a ballpark estimate can be calculated 20 . However , in Figure 2 , a calculated value published by a tank manufacturer is given which roughly coincides with the database value of its constituents 21 . Nevertheless , the most obvious difference between the metals and the FRP is that the end-of-life processing of the wastes
is not considered . It is well-known fact that waste generation and lack of recycling possibilities is a burden for FRP products .
Concluding remarks An interesting observation from this study is that stainless steels , in general , perform very well . The PCFs of regular type 316 , lean duplex 2101 and duplex 2205 are on a similar level to carbon steel , and the low-CO2 versions are also in the same range . Another important discussion point related to the emission levels presented in Figure 2 is that the value proposition for each material varies greatly . Highalloy austenitic stainless steels , nickel and titanium alloys are only considered for critical applications when the environment demands them , while the other materials are more commonly used engineering materials . I would also argue that comparing carbon steel to stainless steel is very much like comparing apples to oranges . It would make more sense to compare similar functional properties . Carbon steel most often requires some form of corrosion protection , such as coatings or linings . A complete LCA is required to consider the impact of the surface protection . The same applies to structural efficiency , which is strongly influenced by which material is chosen . Design strength , modulus of elasticity , and density are important parameters to consider .
Super duplex 2507 is a good example , benefitting from both high strength and high corrosion resistance along with a low CO2e value compared to the other high performance materials . What are the key insights from my study :
• Carbon footprint emission factors for different materials are obtainable , but are they directly comparable ? An EPD should be comparable to another EPD if they are based on the same PCR . In fact , this is not always true as they mostly cover several products , and the declared emissions are based on industry averages rather than specific emissions . PCFs based on ISO 14067 are more specific but not yet generally available for engineering materials . Nevertheless , some representatives of the chemical industry have selected PCF for their products 22 .
• Extensive knowledge about raw material extraction , processing , and the properties of all material candidates is essential to carrying out a reliable LCA .
• It is important that the same functional properties are considered when comparing different materials .
• More guiding principles to support current standards and methodologies are needed to know better how to compare different materials and alloys for a specific application .
• With the above considerations in mind , the PCF emission levels for
34 Stainless Steel World April 2025 www . stainless-steel-world . net