Stainless Steel Background Stainless steel is an iron-containing alloy—a substance made up of two or more chemical elements—used in a wide range of applications.
The austenitic stainless-steel series e. This property comes from its ability to naturally form an oxide-rich, passive layer on the surface. Passivation is a process in which a passive layer forms on the stainless-steel surface; this layer occurs naturally in the presence of oxygen when the surface has been cleaned of exogenous matter 1—3.
The passive layer on the stainless-steel surface becomes the primary means of protection to prevent corrosion. Stainless steel can corrode, however, when the chromium-to-iron ratio has been significantly reduced, resulting in the oxidation and subsequent release of iron oxides that form deposits on surfaces.
Rouge is the commonly used term for the visible corrosion product of stainless steel; it can be composed of several forms of iron oxides, with ferric oxide being the predominant form 4—7. Rouging is typically found in water generation systems, process tanks, and pipeline systems that are routinely exposed to corrosive solutions.
Rouge seems to be a common problem. Regulatory agencies such as FDA have cited in at least one warning letter that corrosion is unacceptable in direct-contact pharmaceutical systems 8. The reasoning is that rouge on product-contact surfaces can create an environment for process residues and microbes to tenaciously adhere to the rouged area and become more difficult to clean and sanitize Residues and microbes might also reside within the rouge layers, where the routine cleaner and sanitizer may not be able to penetrate.
Preventive and corrective maintenance Considering the risk associated with rouged surfaces, manufacturers would benefit from focusing more attention on treatments that prevent rouge from happening. Some companies take a reactive approach and wait until rouge has been detected or has impacted production before taking corrective action.
Process attributes such as elevated temperature, extreme pH solutions, or surface damage e.
If a process or surface condition is expected to lead to corrosion at some point during the life of the equipment, then an effort should be made to investigate and prevent that corrosion from occurring.
Unlike preventive maintenance, which is done to mitigate the cause of the potential problem or undesirable situation, corrective maintenance is done to correct a problem or fault once it has been detected.
With a stainless-steel preventive maintenance procedure, for example, an operator knows exactly what needs to be done at a predefined schedule. On the contrary, in the case of a corrective maintenance, the critical parameters and overall procedure would depend on what is found.
Corrective maintenance often requires evaluation of the severity of the rouge problem before any treatment can be recommended.
This evaluation is referred to as a risk assessment, and includes a review of the potential impact to the patient, product, personnel, and equipment Once the rouge is formed, there may be unknown variables associated with it and correcting the problem typically takes much longer than a preventive task.
Many published references about stainless-steel corrosion are focused on corrective maintenance 3—11, 13— When assessing the risk of the corrosion or rouge to the quality of the next product or batch, one should ask the questions about risk and mitigation actions summarized in Table I.
List of questions to help assess risk. Passivation There is no globally accepted test to guarantee that a stainless-steel surface has been adequately passivated.
Generally, when stainless-steel equipment has been exposed to a passivation treatment, some documentation should be generated describing the passivation procedure with emphasis on the critical parameters.Northern Manufacturing is a sheet metal fabrication company specializing in stainless steel fabrication.
Stainless Steel Pipe, Fittings & Flanges Photography courtesy of Outokumpu, Arcelor, Atlas Steels and New Zealand Tube Mills. Stainless Steel Pipe, Fittings & Flanges. The Advantages of Using Stainless Steel Probably the biggest disadvantage to working with stainless steel is its high upfront cost.
But given how long it will last, that cost is spread out over a longer lifespan than other comparable materials and actually makes stainless steel .
Stainless steel is an alloy of iron with a minimum of % chromium content. Other alloying elements are added to enhance their structure and properties, but fundamentally, stainless steels are considered to be steels with corrosion resistant properties. Stainless steel is an iron-containing alloy—a substance made up of two or more chemical elements—used in a wide range of applications.
It has excellent resistance to stain or rust due to its chromium content, usually from 12 to 20 percent of the alloy. There are more than 57 stainless steels. Deeper than a traditional fry pan, this All-Clad Stainless 4-Quart sauté pan features a large surface area and tall, straight sides that hold in juices, prevent splattering, and allow for easy turning with a .