Additive manufacturing is often assumed to be more sustainable than subtractive production but there has been relatively little evidence to support that claim. Until now. In this article, Bertrand Maillon, Retrofit3D lead at IMI examines the findings from a landmark life cycle assessment completed with environmental consultancy Ricardo in 2023.
Valves are inherently functional. Because of this, it can be easy to overlook their role in ‘big picture’ issues such as climate change. But there’s good reason to make the connection and take it seriously.
Heavy industry – such as refineries and chemicals – is facing growing pressure to decarbonise across the value chain. And research shows much of this pressure is now coming directly from customers.
Valves in good working order also have a major impact on plant performance. According to the European Sealing Association, the non-profit trade body representing manufacturers of sealing devices and materials, control valves account for roughly 60% of a plant’s total emissions. In refineries, this value can increase to 70%, though may only come from 1% of a facility’s total installed assets. (ESA European sealing assoc. Pub. No. 014/05).
These figures are enough for any facility to take action – and is partly why far more attention is now being given to fugitive emissions. But scrutiny cannot end there because there are other ‘hidden’ issues that have a major impact on the sustainability of heavy industry.
Take valve replacement scenarios. Every site, regardless of what’s being produced, will need to regularly maintain, upgrade or change its control valves at some point. This regularity comes with a carbon penalty. With advances to manufacturing techniques, however, there is now scope to drive down embodied carbon, to the point where considerable savings can be made by making relatively minor changes.
It’s this situation that provided the rationale for a life cycle assessment conducted by Ricardo on behalf of IMI. While important intelligence for IMI, the findings also have wider implications for the valve industry and industrial businesses seeking to drive down emissions in line with major targets.
Why analyse valve maintenance in such detail?
Valves can be damaged due to the deleterious phenomena commonly observed in industrial flow control applications. Cavitation is among the most common of these issues and occurs with improper fluid velocity control.
Cavitation in a control valve is damaging, resulting in a potential loss of control and the frequent replacement of spare parts. It can create excessive noise, the erosion of metal parts and pressure transients that result in valve and/or piping vibration and potentially fatigue failure.
When these issues occur, facilities must either repair and replace valve parts or the entire valve itself. Repairs typically involve engineers fitting a new disk stack. Full valve replacement is only needed if the valve’s body is damaged, or when a facility’s process conditions change.
Like-for-like replacement of core internal components is no guarantee of long-term success. This is especially true if the maximum flow velocity isn’t initially managed within the valve, or if the original valve trim is no longer suitable for the current process requirements.
Disk stacks constitute part of a recommended spares programme, allowing a site to operate with minimal downtime. These stacks need replacing more often when fluid velocity control is not maintained, or when a site has an older, poorly designed control valve installed. These valves also wear naturally over time, making it essential to have an adequate maintenance programme in place.
IMI regularly works with customers across the globe to replace faulty valves. As with any effort on this scale, this work has a significant impact on the environment and needs to be measured accurately to ensure that IMI is making legitimate progress on its own climate commitments, as well as those of its customers.
What did the life cycle assessment cover?
Ricardo’s life cycle assessment examined the replacement of a faulty disk stack in a valve manufactured by IMI. The study assessed a large valve (eight inches) and a small valve (three inches) across three different replacement scenarios:
- Replacement of disk stack only via traditional manufacturing methods
- Replacement of the full valve via traditional manufacturing methods
- Replacement of the disk stack only via additive manufacturing
Full valve replacement included replacing the disk stack, body and bonnet, while the other two replacement scenarios only involved changes to the disk stack.
The life cycle assessment was a cradle-to-grave study. However, the valve’s use phase was excluded because data was not available to support claims that different replacement scenarios have different use efficiency savings. As such, the study only examined the sourcing and production of raw materials required for each replacement scenario, manufacturing inputs, the transport of parts between sites and the end-of-life fate of finished parts, including transportation to a disposal location.
Setting the metrics
There are several ways to measure the environmental impact of a product or industrial process. Climate Change Impact (also known as Global Warming Potential) is arguably the most significant. Carbon dioxide equivalent (abbreviated as CO2-eq) is a metric measure used to compare the emissions from various greenhouse gases on the basis of their CCP/GWP.[1] CO2-eq is the principal metric given in Ricardo’s final report.
Disk stacks, which can be either traditionally or additively manufactured, require different levels of maintenance and yield different lifetimes. This means that under a specific replacement scenario, a valve can last a certain time before it needs to be replaced or upgraded.
IMI had to make some assumptions based on existing knowledge in this field, which were supplied to Ricardo. The table above provides a breakdown of the three replacement scenarios covered in this study.
As the table shows (Fig. 1), a traditionally manufactured replacement disk stack is assumed to last one year. Any facility using this replacement scenario would therefore need 10 new disk stacks over the set study horizon of 10 years. The full valve replacement is only required once, while disk stacks manufactured additively would need replacing twice over the 10-year period. Ricardo factored in these differences when analysing the replacement scenarios as part of a sensitivity study, provided in the appendix of its report.
The additive advantage
Ricardo’s life cycle assessment found that the additive disk stack replacement manufactured by Retrofit3D – IMI’s additive manufacturing valve trim solution – was the preferable scenario across all the environmental indicators analysed. This finding was the same for both the large and small valve categories used in the study.
In other words, additively manufactured disk stacks should be considered environmentally advantageous when compared with the other valve replacement methods. This is due to the different materials used and the lower quantities needed to produce them.
The small valve with an additive disk stack replacement had a Climate Change Impact of 146kg of CO2-eq, while the large valve with an additive disk stack replacement recorded 1,360kg CO2-eq. Both of these figures were calculated based on the 10-year study horizon.
For the large valve, this represented:
- A 96% Climate Change Impact saving when compared with replacement of the full valve via traditional manufacturing.
- A 94% Climate Change Impact saving when compared with replacement of the disk stack only via traditional manufacturing.
For the small valve, this represented:
- An 87% Climate Change Impact saving when compared with replacement of the full valve via traditional manufacturing.
- An 85% Climate Change Impact saving when compared with replacement of the disk stack only via traditional manufacturing.
Unsurprisingly, for the large valve, the least favourable scenario in terms of Climate Change Impact was replacement of the full valve at 34,000kg CO2-eq. This was due to the body component, which required more material and resources ahead of delivery to a customer site.
For the small valve results, however, the traditional disk stack replacement was the least favourable option. It contributed 1,130 CO2-eq. This is noticeably more than the 988kg CO2-eq for the full valve replacement. This was due to the raw materials required for replacing 10 traditional disk stacks over the 10-year period.
Extra work was carried out to determine the sensitivity of these results against assumptions made about the mode of transport, valve lifetimes and the frequency of replacement. Even with these factors, the additive replacement scenario still proved favourable.
Consideration was also given to assumptions about the frequency of replacements. Even with a ‘tipping point’ factored into the results, the additive disk stack still outperformed the other two scenarios. It was determined that an additive disk stack would need to be replaced every two or three months to be less favourable than the traditional replacement options.
For more information on Retrofit3D, here.
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