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Nitric Acid Passivation and EH&S Impact
P.E. REM, Hixson Inc.
Q. I am looking for safety/environmental requirements to set up a nitric acid cleaning and passivation system. K.A.
A. According to ASTM A380 - 06 Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems, passivation is:
... the removal of exogenous iron or iron compounds from the surface of a stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination but will not significantly affect the stainless steel itself.”
The standard also describes passivation as:
... the chemical treatment of stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing spontaneous formation of the protective passive film.
The purpose is to remove the “free iron” on the surface of stainless steel left behind from machining and fabrication. Left attached, this free iron becomes a site for potential corrosion and deterioration. During passivation, a thin, oxide film is also formed that protects stainless steel from corrosion.
Fumes and More Fumes
As to be expected, installing a nitric acid cleaning and passivation system in your facility potentially exposes you to a significant number of environmental regulations and safety concerns.
Nitric acid passivation creates fumes that contain nitric acid mist droplets and nitrogen dioxide and nitric oxide gases, which are considered air pollutants. While you may be able to use general area ventilation or local ventilation of the passivation tank to control fume exposure to your employees, it is imperative that you determine your state’s air pollution control requirements. Pollution control agencies now require Best Available Technology (BAT) to be employed to control nitric acid and NOx. Depending on the size of the line you install and its emission rates for these pollutants, BAT could be either a single-stage (small source) or two-state (large source) scrubber. Unless you determine that the source emissions are below your state’s exempt emissions level, you will need to obtain an air pollution permit from the state to install and operate the system.
It is highly recommended that you engage an environmental professional familiar with your state’s air pollution regulations and your process to determine if a permit is required and what level of control is needed.
Wastewater generated from the passivation process will be regulated under the U.S. EPA’s Metal Finishing Categorical Standards (40 CFR 433) as well as your Publicly Owned Treatment Works’ (POTW) local limits, assuming you are discharging to a sanitary sewer system. If your POTW has control authority in your state, you will definitely require a local wastewater discharge permit. If the state has control authority, you will need to obtain a state wastewater discharge permit. Some states require facilities to obtain a separate permit to Install as well as operator certification for wastewater pretreatment systems. If you directly discharge your wastewater to surface waters, a National Pollutant Discharge Elimination System (NPDES) permit as well as wastewater operator licensing will be required from the state or EPA.
Nickel and chromium will definitely be found in your wastewater stream at levels that exceed permitted limits. Based on the chemicals used in the passivation process and the nickel and chromium content of stainless steel, the likely wastewater pretreatment regime will be pH adjustment, metal precipitation, coagulation, flocculation and solids separation.
One issue that is sometimes overlooked is the question of how wastewater will be sampled. The wastewater discharge from your passivation process will require periodical compliance sampling and analysis. Usually, automatic flow proportional sampling (sampling every “x” gallons of discharge) utilizing an automatic sampler with flow meter is required by the POTW or state, but sometimes time proportional sampling (sampling every “x” minutes) is acceptable. If discharge flow is small, you should consider installing a holding tank capable of holding one day’s flow volume and then batch discharge; manual grab samples would be collected during the discharge. If you want to evaluate eliminating or reducing wastewater treatment, refer to my article in the Products Finishing Directory and Technology Guide titled “Recovery/Recycling Methods for Platers.” Some of these methods apply to passivation.
It is also good engineering practice to install both the process line and the wastewater treatment system within containment area(s). The containment area(s) are to be covered with a protective coating and/or liner system in order to prevent hazardous chemicals from destroying the underlying concrete floor and, worse, leak into the ground, resulting in very expensive cleanup and decontamination.
Let’s Talk About Sludge
Sludge generated during the wastewater treatment process will be regulated as an F006-listed hazardous waste (wastewater treatment sludges from electroplating operations, unless specifically exempted). In addition, if you decide to ship waste nitric acid, cleaning solutions and passivation solutions off site, they would be required to be handled as hazardous waste based upon corrosivity and chromium content. Unless you consistently generate less than 220 lbs. (100 kg) of hazardous wastes per month, you will need to obtain an EPA ID number. However, many states require all hazardous waste generators to obtain EPA ID numbers. Small-quantity hazardous waste generators (220-2,200 lbs./month) have only a few EPA requirements to meet regarding storage and transportation, while large-quantity hazardous waste generators (greater than 2,200 lbs./month) have numerous requirements, including formal training and contingency planning. EPA has relaxed some of the hazardous waste generator requirements for facilities that recycle their F006 wastes. Based upon your waste’s chromium and nickel content, you may be able to have your sludge “recycled” at a metals recovery facility. If you decide to send your waste nitric acid off site for disposal, there are facilities that recover the nitric acid as well as the metals.
Additional reporting requirements also will likely be triggered by the installation of a passivation system. Any facility that stores any of the extremely hazardous substances (EHS) specified in Section 302 of the Emergency Planning and Community Right-to-Know Act (EPCRA) in a quantity greater than its threshold planning quantity (TPQ) is subject to the notification requirements specified in this section (and state law). Nitric acid is considered an EHS with a TPQ of only 500 lbs. If the amount of nitric acid on site exceeds its 500-lb. threshold, you will need to submit a one-time notification to your local fire department, local emergency planning committee and state emergency response commission within 60 days of becoming applicable. Nitric acid also will be required to be reported to the same three agencies on an annual SARA Tier II report, due annually by March 1 of the succeeding year.
Manufacturing facilities which manufacture, process or otherwise use any of the chemicals specified in EPCRA Section 313 (and state law) in quantities which exceed the thresholds of 10,000 lbs. per year used, 25,000 lbs. per year manufactured or processed, or other chemical-specific thresholds, are subject to the annual reporting requirements of this section. Detailed calculations and estimates of releases to land, water and air for nitric acid, nitrates (generated by the neutralization of nitric acid), nickel and chromium will likely be required for releases from the passivation system. If required, the report must be submitted to state and EPA by July 1 of the succeeding year.
You also asked for some information on safety requirements. As I am sure you are anticipating, there are several health and safety risks associated with operating a passivation system. First, as discussed above, proper ventilation and exhaust is crucial to protecting your employees. It is also crucial to protecting building structures, as acid fumes can cause structural damage to building components. Without proper ventilation and exhaust, and personal protective equipment (PPE), your employees may be exposed to nitric acid and NOx, which cause damage to the respiratory system. Adequate control equipment should always take priority over personal protection equipment. However, if control equipment is not sufficient for keeping contaminant concentrations below the permitted workplace exposure thresholds, a suitable respiratory protection program must be implemented.
Because of new chemicals introduced into the workplace, your hazard communication program and training will need to be revised in order to incorporate the hazards of the passivation process. Skin and eye protection must also be addressed because of exposure to nitric acid. It is recommended that personnel working near the tanks wear a hood visor or protective visor together with safety goggles, safety apron, long acid-resistant work gloves, long-sleeved overalls and safety footwear. An emergency eye-washing and shower station must also be provided.
Depending on the height of your tanks and location, guarding may need to be installed to prevent an employee from falling into a tank. In CFR 1910.23(c)(3) OSHA states that “regardless of height, open-sided floors, walkways, platforms, or runways above or adjacent to dangerous equipment, pickling or galvanizing tanks, degreasing units, and similar hazards shall be guarded with a standard railing and toe board.” Any tank with a rim lower than 42” requires a safety rail.
You will also need to determine if your tanks are considered confined spaces. Although the 29 CFR 1910.146 definition of confined space is quite vague, for tanks/vats I use a rule-of-thumb of 4 ft. in height or depth. Typically at this depth and below, the likelihood of someone being overcome by atmospheric hazards is extremely unlikely, especially with this process. You must also determine if a confined space should be considered a permit-required confined space; these are spaces that could potentially contain a hazard (i.e., oxygen-deficient, flammable vapor or toxic vapor) during an entry operation. If it is determined that you do have a permit-required confined space, refer to the above OSHA standard for additional information on program implementation requirements.
As you can see, there are many environmental health and safety facets to consider when looking at the installation of a nitric acid passivation system. There is an alternative method of passivation that you may want to consider. Citric acid passivation eliminates many of the health and environmental hazards that are associated with nitric acid passivation. There is a lot of information available on the effectiveness and application of citric acid passivation. Here is a link to further information on citric acid passivation provided by a Products Finishing reader that was included in the January 2010 edition: controlelectropolishing.com/CEC_Pollution_Prevention.pdf
Unless you have the in-house expertise and time to properly evaluate these, as well as other EH&S issues that space prevented me from discussing, it is my strong recommendation that you engage an EH&S professional that also understands your process and get them onto your team as early as possible. This professional can give you great advice and value so that your project’s budget is more accurate and a practical schedule is established, and to steer the project around the regulatory and bureaucratic minefield. Good Luck.