Application Note
Does pure water have a corrosive impact on stainless-steel lab equipment?
Authors
Merina Corpinot PhD,1 Estelle Riche PhD,2 Christopher Colin,1 Cecilia Devaux,1 Stephane Mabic PhD2 R&D1 and Marketing2, Lab Water Solutions, MilliporeSigma, Guyancourt, France 2
Introduction: Feed water quality for laboratory equipment
Laboratory equipment, such as washers, autoclaves, sterilizers, heating baths and testing chambers (environmental and humidity chambers), require water of good and consistent quality to work properly and efficiently, especially with respect to laboratory application and performance requirements.
Several factors can influence the type of water used to feed laboratory equipment. These include manufacturer recommendations (specific pH ranges, resistivity, etc.), standards (e.g., EN 13060), the equipment material of construction and its corrosion resistance, equipment design, equipment environment, and the time exposed to water.
Using pure water that is low in the following contaminants will contribute to extend equipment lifetime and proper functioning:
• Ions such as minerals (e.g., calcium, magnesium, iron, manganese) may form scale or mineral deposits inside the equipment or on samples, which can eventually cause system failure and affect test results.
• Particles and colloids can generate aggregates and form hard deposits.
• Silica can be particularly detrimental to some equipment (e.g., dishwashers, weathering and stability testing chambers). In washers, for example, silica deposit can form on glassware and cause discoloration inside the instrument and the labware.
• Organic molecules should be minimized to avoid soiling the equipment, leading to more frequent maintenance.
Water purification systems generally employ a combination of purification technologies to remove these contaminants from tap water, including reverse osmosis (RO), deionization (DI) or electrodeionization (EDI), and bactericidal UV. The Elix® EDI module is particularly critical to the system’s reliability as it ensures constant-quality pure water while requiring no maintenance, such as chemical regeneration, or resin or DI cartridge changes. Elix® pure water is consistently low in ions (resistivity > 5 MΩ·cm @ 25 °C) and low in organics.
Study: Suitability of Elix® pure water on stainless steel
Users of laboratory equipment may wonder if stainless steel is resistant or unaffected by Elix® pure water, as the ability of high-purity water to corrode stainless steel or other metals has been studied,1-6 especially in the pharmaceutical industry where the “rouging phenomenon” is an issue.7 To address this concern, we performed a study to document the suitability of Elix® pure water to feed laboratory equipment. We aimed to mimic the interior of laboratory equipment by assessing this water’s impact on stainless-steel plates.
Method: Testing the corrosive impact of pure water on stainless steel
Immersion corrosion testing method
To evaluate the potential corrosion impact of Elix® pure water on stainless steel, we used accelerated corrosion testing conditions (80 °C), stainless-steel welded plates (“coupons”), and followed an immersion procedure (similar to DIN EN 50905 standard used in industry).8
Elix® pure water was produced with a system that employs a combination of purification technologies, including advanced RO, Elix® EDI and a bactericidal UV lamp, similar to a Milli-Q® IX water system. Two grades of stainless-steel coupons were tested:
• AISI 316L: High grade, more resistant to corrosion; composition: 16% chromium, 10% nickel, 2% molybdenum; also known as EN 1.4404.
• AISI 304L: Lower grade, less resistant to corrosion; composition: 18% chromium, 8% nickel; also known as EN 1.4301.
To increase the likelihood of corrosion, weakened areas were produced by creating a welding zone on each coupon.
The stainless-steel coupons (3 replicates) were immersed in Elix® pure water for 52 weeks, as shown in Figure 1. Water was changed every week to increase the risk of corrosion. Samples were placed in a laboratory oven at 80 °C. Two control coupons (one of each steel grade) were let standing: (a) at room temperature and not immersed in water and (b) at 80 °C and not immersed in water. A bottle of Elix® pure water with no coupon was also included as control. Figure 2 summarizes the study design.
During the exposure period, coupons were visually inspected for any changes and pictures were taken. At each water change, conductivity was measured. Coupons were weighed every week to monitor weight loss, after being removed from water and let to dry. Independent testing to identify potential corrosion was performed by CETIM (industrial technical center expert laboratory) using Scanning Electronic Microscopy (SEM) at the beginning of the experiment (T0) and after 52 weeks (T52). When required, energy-dispersive X-ray spectroscopy (EDS) was used to obtain an elemental characterization of the samples, also performed by CETIM.
Figure 1. Experimental set up showing a stainless-steel coupon immersed in water.
Figure 2. Experimental setup to evaluate the corrosive impact of Elix® pure water on stainless steel. The numbers 1 to 5 represent the reference of each coupon.
Results: Corrosion testing
Visual inspection
We analyzed by visual inspection the coupons made of AISI 304L and AISI 316L grade stainless steel, which had been immersed in Elix® pure water or left not immersed (controls). After 52 weeks of exposure, we observed no sign of corrosion on any of the stainlesssteel coupons. Pictures of the AISI 304L control coupon and AISI 304L coupon immersed in Elix® pure water are shown in Figure 3 as examples.
Other analytical assessments
Other techniques, such as SEM and EDS, as well as weight and conductivity measurements also confirmed the absence of corrosion sites, even at the welded joints, which are considered more susceptible to corrosion.
The conductivity of the Elix® pure water control placed at 80 °C for one week was similar to the conductivity of samples (1), (2) and (3) respectively, over 52 weeks. This shows that the presence of the stainlesssteel coupons does not impact water quality, thus no corrosion reaction could be deducted.
Conclusion: Elix® pure water does not corrode stainless steel
Both internal investigations and external expertise concluded that neither high-grade (AISI 316L) nor lower-grade (AISI 304L) stainless steel were corroded after one year of immersion in Elix® pure water at 80 °C (accelerated corrosion testing conditions). This indicates that the quality of Elix® pure water does not impede the integrity of lab equipment in the tested conditions if made of either of these stainless-steel qualities compared to other less resistant metals (copper,1,2 brass, etc.) which may corrode.
Benefits of Elix® pure water to feed lab equipment
Using Elix® pure water, obtained with EDI technology, offers the benefits of delivering the appropriate and consistent quality water to feed different types of laboratory equipment made of high-quality material such as stainless steel, without the risk of corrosion. Other benefits of water purification systems embedding Elix® EDI module include assured reliable performance, carefree maintenance, and simplified traceability, which are especially critical for regulated and highly productive environments.
Figure 3. Photos of test and control plates (front and back views) made of AISI 304L (EN 1.4301) grade stainless steel at 0, 26 and 52 weeks. (a-c) Test plate placed at 80 °C immersed in Elix® pure water; (d-e) Control plate placed at 80 °C with no water; (g-i) Control plate placed at room temperature (RT) with no water. No signs of corrosion were observed on any of the plates.
References
1. Cavallini C, Gasparrini C, Zaupa M, et al. Corrosion and Metal Release of Copper and Stainless Steel Exposed to Ultrapure Water. IEEE Trans Plasma Sci 2022;50(11):4491-5. doi:10.1109/TPS.2022.3182804
2. Ottosson M, Boman M, Berastegui P, et al. Copper in ultrapure water, a scientific issue under debate. Corros Sci 2017;122:53-60. doi.org/10.1016/j.corsci.2017.03.014
3. Yang HL, Cunxiong L, Chang W, et al. Molybdenum blue photometry method for the determination of colloidal silica and soluble silica in leaching solution. Anal Methods 2015;7:5462-7. doi.org/10.1039/C5AY01306B
4. Mantzavinos D, Hodgkiess T, Lai SLC. Corrosion of condenser tube materials in distilled water. Desalination 2001;138:365–70. doi. org/10.1016/S0011-9164(01)00285-5
5. Hodgkiess T, Mantzavinos D. Corrosion of copper-nickel alloys in pure water. Desalination 1999;126:129–37. doi.org/10.1016/S0011-9164(99)00165-4
6. Eriksen TE, Ndalamba P, Grenthe I. On the corrosion of copper in pure water. Corros Sci 1989;29: 1241–50.doi.org/10.1016/0010-938X(89)90071-1
7. Zaffora A, Di Franco F, Santamaria M. Corrosion of stainless steel in food and pharmaceutical industry. Curr Opin Electrochem 2021;29:100760. doi.org/10.1016/j.coelec.2021.100760
8. DIN 50905-1 - European Standards. Korrosion der Metalle - Korrosionsuntersuchungen - Teil 1: Grundsätze. 2022-09.
www.en-standard.eu/din-50905-1-korrosion-der-metallekorrosionsuntersuchungen-teil-1-grundsatze/
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