Passivation

Stainless Steel Passivation with HNO₃

Just because a metal is deemed stainless doesn't mean it won't rust. Low, even high-grade stainless steels will develop some rust if exposed to free iron contaminants. Free iron contaminants can come from the atmosphere (common in manufacturing environments where carbon steel and iron is milled, ground or machined), tap water, grinding tools (that have been used on carbon steel), and from the stainless steel composition itself.

NTS is an aerospace and industry approved passivation source, with 40 years of evolving experience. In the last two decades, chromated solutions have became a disposal impossibility and recently the U.S. Defense Department has canceled the QQ-P-35 standard ("Passivation Treatment for Corrosion-Resistant Steel"). As passivation with nitric acid solution or past (HNO₃) has changed, NTS has perfected successful methods in implementing the practices in the now prevalent ASTM A-380 ("Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems") and ASTM A-967 ("Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts") standards for cleaning, descaling and passivation of stainless steel parts and systems. Care is taken to properly degrease surfaces to be treated, and even greater care is taken to thoroughly rinse all surfaces to arrest the process. NTS is an expert in difficult to reach areas and combinations where one surface receives passivation and an immediately adjoining surface does not. No matter if it's a simple part or a complex assembly, your result will be a rust resistant, passive oxide film exactly where it was intended to be.

Stainless Steel Passivation with Citric Acid

More than 99% of the citric acid sold in the US is used in food and beverage products. While this may seem a testimony to its safety, it is actually a testimonial of its effectiveness. When formulated properly, citric acid passivation will perform better than nitric acid - and the food industry requires the best, otherwise systems degrade and the taste of food products suffers. Moreover, using a citric acid process for passivation eliminates all risk to personnel and much of the risk to parts (generally unless surfaces are exposed longer than necessary). In addition, on large systems where field services crew and large volumes of fluid are required, citric acid is a far more economical way of passivating stainless steel. Plus citric acid removes iron from the surface effectively in much lower concentrations than nitric acid does. A typical solution of citric is only 4-10% by weight; hence disposal requires only the dilution that naturally occurs during the rinse cycle. The resulting effluent is very close to industrial wastewater.

Another widely recognized advantage of using citric acid is its ability to remove free iron and iron oxides without removing significant amounts of nickel, chromium, or other heavy metals. Thanks to the pioneering work in Germany for beverage container passivation, the citric acid process has shown to be advantageous for fasteners, medical devices, semi-conductor, automotive and aerospace applications.

NTS chooses to employ the citric process in almost all its field applications in order to save our clients money, protect the environment (nitrogen oxides promote smog while citric acid does not harm the atmosphere), and speed up the process (faster processing and easier disposal).

Carbon Steel & Other Metals

Carbon steel benefits from a process similar to the citric acid passivation performed on stainless steel. A properly formulated solution performed at the right temperature can greatly reduce corrosiveness of carbon steel. The process is particularly successful in piping systems where the first step - cleaning and descaling - is part of the cleaning requirement.

In carbon steel treatment as well as that of other metals, NTS will quite literally be the solution to your contamination problem. Give us a call for phosphate coating on carbon steel surfaces (compressed oxygen use), or specialized chemistry for passivation of nickel, copper, and other metals.

Contact NTS today for more information!

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