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Pure or pure steam pharmaceutical systems include generators, control valves, distribution pipes or pipelines, thermodynamic or equilibrium thermostatic traps, pressure gauges, pressure reducers, safety valves, and volumetric accumulators.
Most of these parts are made of 316 L stainless steel and contain fluoropolymer gaskets (typically polytetrafluoroethylene, also known as Teflon or PTFE), as well as semi-metal or other elastomeric materials.
These components are susceptible to corrosion or degradation during use, which affects the quality of the finished Clean Steam (CS) utility. The project detailed in this article evaluated stainless steel specimens from four CS system case studies, assessed the risk of potential corrosion impacts on process and critical engineering systems, and tested for particulates and metals in condensate.
Samples of corroded piping and distribution system components are placed to investigate corrosion by-products. 9 For each specific case, different surface conditions were evaluated. For example, standard blush and corrosion effects were evaluated.
The surfaces of the reference samples were assessed for the presence of blush deposits using visual inspection, Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).
These methods can reveal the physical and atomic properties of corrosion and deposits, as well as determine the key factors that affect the properties of technical fluids or end products. one
Corrosion products of stainless steel can take many forms, such as a carmine layer of iron oxide (brown or red) on the surface below or above the layer of iron oxide (black or grey)2. Ability to migrate downstream.
The iron oxide layer (black blush) may thicken over time as the deposits become more pronounced, as evidenced by particles or deposits visible on the surfaces of the sterilization chamber and equipment or containers after steam sterilization, there is migration. Laboratory analysis of condensate samples showed the dispersed nature of the sludge and the amount of soluble metals in the CS fluid. four
Although there are many reasons for this phenomenon, the CS generator is usually the main contributor. It is not uncommon to find red iron oxide (brown/red) on surfaces and iron oxide (black/grey) in vents that slowly migrate through the CS distribution system. 6
The CS distribution system is a branching configuration with multiple usage points ending at remote areas or at the end of the main header and various branch subheaders. The system may include a number of regulators to help initiate pressure/temperature reduction at specific points of use that may be potential corrosion points.
Corrosion can also occur in hygienic design traps that are placed at various points in the system to remove condensate and air from flowing clean steam through the trap, downstream piping/discharge piping or condensate header.
In most cases, reverse migration is likely where rust deposits build up on the trap and grow upstream into and beyond adjacent pipelines or point-of-use collectors; rust that forms in traps or other components can be seen upstream of the source with constant migration downstream and upstream.
Some stainless steel components also exhibit various moderate to high levels of metallurgical structures, including delta ferrite. Ferrite crystals are believed to reduce corrosion resistance, even though they may be present in as little as 1–5%.
Ferrite is also not as resistant to corrosion as the austenitic crystal structure, so it will preferentially corrode. Ferrites can be accurately detected with a ferrite probe and semi-accurate with a magnet, but there are significant limitations.
From system setup, through initial commissioning, and the startup of a new CS generator and distribution piping, there are a number of factors that contribute to corrosion:
Over time, corrosive elements such as these can produce corrosion products when they meet, combine, and overlap with mixtures of iron and iron. Black soot is usually seen first in the generator, then it appears in the generator discharge piping and eventually throughout the CS distribution system.
SEM analysis was performed to reveal the microstructure of corrosion by-products covering the entire surface with crystals and other particles. The background or underlying surface on which the particles are found varies from various grades of iron (Fig. 1-3) to common samples, namely silica/iron, sandy, vitreous, homogeneous deposits (Fig. 4). The steam trap bellows were also analyzed (Fig. 5-6).
AES testing is an analytical method used to determine the surface chemistry of stainless steel and diagnose its corrosion resistance. It also shows the deterioration of the passive film and the decrease in the concentration of chromium in the passive film as the surface deteriorates due to corrosion.
To characterize the elemental composition of the surface of each sample, AES scans (concentration profiles of surface elements over depth) were used.
Each site used for SEM analysis and augmentation has been carefully selected to provide information from typical regions. Each study provided information from the top few molecular layers (estimated at 10 angstroms [Å] per layer) to the depth of the metal alloy (200–1000 Å).
Significant amounts of iron (Fe), chromium (Cr), nickel (Ni), oxygen (O) and carbon (C) have been recorded in all regions of Rouge. AES data and results are outlined in the case study section.
The overall AES results for the initial conditions show that strong oxidation occurs on samples with unusually high concentrations of Fe and O (iron oxides) and low Cr content on the surface. This ruddy deposit results in the release of particles that can contaminate the product and surfaces in contact with the product.
After the blush was removed, the “passivated” samples showed a complete recovery of the passive film, with Cr reaching higher concentration levels than Fe, with a Cr:Fe surface ratio ranging from 1.0 to 2.0 and an overall absence of iron oxide.
Various rough surfaces were analyzed using XPS/ESCA to compare elemental concentrations and spectral oxidation states of Fe, Cr, sulfur (S), calcium (Ca), sodium (Na), phosphorus (P), nitrogen (N), and O. and C (table A).
There is a clear difference in Cr content from values ​​close to the passivation layer to lower values ​​typically found in base alloys. The levels of iron and chromium found on the surface represent different thicknesses and grades of rouge deposits. XPS tests have shown an increase in Na, C or Ca on rough surfaces compared to cleaned and passivated surfaces.
XPS testing also showed high levels of C in iron red (black) red as well as Fe(x)O(y) (iron oxide) in red. XPS data is not useful for understanding surface changes during corrosion because it evaluates both the red metal and the base metal. Additional XPS testing with larger samples is required to properly evaluate results.
Previous authors also had difficulty evaluating XPS data. 10 Field observations during the removal process have shown that the carbon content is high and is usually removed by filtration during processing. SEM micrographs taken before and after wrinkle removal treatment illustrate the surface damage caused by these deposits, including pitting and porosity, which directly affect corrosion.
The XPS results after passivation showed that the Cr:Fe content ratio on the surface was much higher when the passivation film was re-formed, thereby reducing the rate of corrosion and other adverse effects on the surface.
The coupon samples showed a significant increase in the Cr:Fe ratio between the “as is” surface and the passivated surface. Initial Cr:Fe ratios were tested in the range of 0.6 to 1.0, while post-treatment passivation ratios ranged from 1.0 to 2.5. The values ​​for electropolished and passivated stainless steels are between 1.5 and 2.5.
In the samples subjected to post-processing, the maximum depth of the Cr:Fe ratio (established using AES) ranged from 3 to 16 Å. They compare favorably with data from previous studies published by Coleman2 and Roll. 9 The surfaces of all samples had standard levels of Fe, Ni, O, Cr, and C. Low levels of P, Cl, S, N, Ca, and Na were also found in most of the samples.
These residues are typical of chemical cleaners, purified water, or electropolishing. Upon further analysis, some silicon contamination was found on the surface and at different levels of the austenite crystal itself. The source appears to be the silica content of the water/steam, mechanical polishes, or dissolved or etched sight glass in the CS generation cell.
Corrosion products found in CS systems are reported to vary greatly. This is due to the varying conditions of these systems and the placement of various components such as valves, traps and other accessories that can lead to corrosive conditions and corrosion products.
In addition, replacement components are often introduced into the system that are not properly passivated. Corrosion products are also significantly affected by the design of the CS generator and the quality of the water. Some types of generator sets are reboilers while others are tubular flashers. CS generators typically use end screens to remove moisture from clean steam, while other generators use baffles or cyclones.
Some produce an almost solid iron patina in the distribution pipe and the red iron covering it. The baffled block forms a black iron film with an iron oxide blush underneath and creates a second top surface phenomenon in the form of a sooty blush that is easier to wipe off the surface.
As a rule, this ferruginous-soot-like deposit is much more pronounced than the iron-red one, and is more mobile. Due to the increased oxidation state of the iron in the condensate, the sludge generated in the condensate channel at the bottom of the distribution pipe has iron oxide sludge on top of the iron sludge.
The iron oxide blush passes through the condensate collector, becomes visible in the drain, and the top layer is easily rubbed off the surface. Water quality plays an important role in the chemical composition of blush.
Higher hydrocarbon content results in too much soot in lipstick, while higher silica content results in higher silica content, resulting in a smooth or glossy lipstick layer. As mentioned earlier, water level sight glasses are also prone to corrosion, allowing debris and silica to enter the system.
The gun is a cause for concern in steam systems as thick layers can form which form particles. These particles are present on steam surfaces or in steam sterilization equipment. The following sections describe possible drug effects.
The As-Is SEMs in Figures 7 and 8 show the microcrystalline nature of class 2 carmine in case 1. A particularly dense matrix of iron oxide crystals formed on the surface in the form of a fine-grained residue. Decontaminated and passivated surfaces showed corrosion damage resulting in a rough and slightly porous surface texture as shown in Figures 9 and 10.
NPP scan in fig. 11 shows the initial state of the original surface with heavy iron oxide on it. The passivated and derouged surface (Figure 12) indicates that the passive film now has an elevated Cr (red line) content above the Fe (black line) at > 1.0 Cr:Fe ratio. The passivated and derouged surface (Figure 12) indicates that the passive film now has an elevated Cr (red line) content above the Fe (black line) at > 1.0 Cr:Fe ratio. Пассивированная и обесточенная поверхность (рис. 12) указывает на то, что пассивная пленка теперь имеет повышенное содержание Cr (красная линия) по сравнению с Fe (черная линия) при соотношении Cr:Fe > 1,0. The passivated and de-energized surface (Fig. 12) indicates that the passive film now has an increased content of Cr (red line) compared to Fe (black line) at a ratio of Cr:Fe > 1.0.钝化和去皱表面（图12）表明，钝化膜现在的Cr（红线）含量高于Fe（黑线），Cr:Fe 比率> 1.0。 Cr（红线）含量高于Fe（黑线），Cr:Fe 比率> 1.0。 Пассивированная и морщинистая поверхность (рис. 12) показывает, что пассивированная пленка теперь имеет более высокое содержание Cr (красная линия), чем Fe (черная линия), при соотношении Cr:Fe > 1,0. The passivated and wrinkled surface (Fig. 12) shows that the passivated film now has a higher Cr content (red line) than Fe (black line) at a Cr:Fe ratio > 1.0.
A thinner (< 80 Å) passivating chromium oxide film is more protective than a hundreds of angstrom thick crystalline iron oxide film from a base metal and scale layer with an iron content of more than 65%.
The chemical composition of the passivated and wrinkled surface is now comparable to passivated polished materials. The sediment in case 1 is a class 2 sediment capable of being formed in situ; as it accumulates, larger particles are formed that migrate with the steam.
In this case, the corrosion shown will not lead to serious flaws or deterioration of the surface quality. Normal wrinkling will reduce the corrosive effect on the surface and eliminate the possibility of strong migration of particles that may become visible.
In Figure 11, AES results show that thick layers near the surface have higher levels of Fe and O (500 Å of iron oxide; lemon green and blue lines, respectively), transitioning to doped levels of Fe, Ni, Cr, and O. Fe concentration (blue line) is much higher than that of any other metal, increasing from 35% at the surface to over 65% in the alloy.
At the surface, the O level (light green line) goes from almost 50% in the alloy to almost zero at an oxide film thickness of more than 700 Å. The Ni (dark green line) and Cr (red line) levels are extremely low at the surface (< 4%) and increase to normal levels (11% and 17%, respectively) at alloy depth. The Ni (dark green line) and Cr (red line) levels are extremely low at the surface (< 4%) and increase to normal levels (11% and 17%, respectively) at alloy depth. Уровни Ni (темно-зеленая линия) и Cr (красная линия) чрезвычайно низки на поверхности (<4%) и увеличиваются до нормального уровня (11% и 17% соответственно) в глубине сплава. Levels of Ni (dark green line) and Cr (red line) are extremely low at the surface (<4%) and increase to normal levels (11% and 17% respectively) deep in the alloy.表面的Ni（深绿线）和Cr（红线）水平极低（< 4%），而在合金深度处增加到正常水平（分别为11% 和17%）。表面的Ni（深绿线）和Cr（红线）水平极低（< 4%），而在合金深度处增加到歌常水平（分别咺11% Уровни Ni (темно-зеленая линия) и Cr (красная линия) на поверхности чрезвычайно низки (<4%) и увеличиваются до нормального уровня в глубине сплава (11% и 17% соответственно). Levels of Ni (dark green line) and Cr (red line) at the surface are extremely low (<4%) and increase to normal levels deep in the alloy (11% and 17% respectively).
AES image in fig. 12 shows that the rouge (iron oxide) layer has been removed and the passivation film has been restored. In the 15 Å primary layer, the Cr level (red line) is higher than the Fe level (black line), which is a passive film. Initially, the Ni content on the surface was 9%, increasing by 60–70 Å above the Cr level (± 16%), and then increasing to the alloy level of 200 Å.
Starting at 2%, the carbon level (blue line) drops to zero at 30 Å. The Fe level is initially low (< 15%) and later equal to the Cr level at 15 Å and continues to increase to the alloy level at more than 65% at 150 Å. The Fe level is initially low (< 15%) and later equal to the Cr level at 15 Å and continues to increase to the alloy level at more than 65% at 150 Å. Уровень Fe вначале низкий (< 15%), позже равен уровню Cr при 15 Å и продолжает увеличиваться до уровня сплава более 65% при 150 Å. The Fe level is initially low (< 15%), later equals the Cr level at 15 Å and continues to increase to over 65% alloy level at 150 Å. Fe 含量最初很低(< 15%)，后来在15 Å 时等于Cr 含量，并在150 Å 时继续增加到超过65% 的合金含量。 Fe 含量最初很低(< 15%)，后来在15 Å 时等于Cr 含量，并在150 Å 时继续增加到超过65% 的合金含量。 Содержание Fe изначально низкое (< 15 %), позже оно равняется содержанию Cr при 15 Å и продолжает увеличиваться до содержания сплава более 65 % при 150 Å. The Fe content is initially low (< 15%), later it equals the Cr content at 15 Å and continues to increase until the alloy content is over 65% at 150 Å. Cr levels increase to 25% of the surface at 30 Å and decrease to 17% in the alloy.
The elevated O level near the surface (light green line) decreases to zero after a depth of 120 Å. This analysis demonstrated a well developed surface passivation film. The SEM photographs in figures 13 and 14 show the rough, rough and porous crystalline nature of the surface 1st and 2nd iron oxide layers. The wrinkled surface shows the effect of corrosion on a partially pitted rough surface (Figures 18-19).
The passivated and wrinkled surfaces shown in figures 13 and 14 do not withstand severe oxidation. Figures 15 and 16 show a restored passivation film on a metal surface.