The primary reason for self-performing pickling is time and cost savings. But in practice, the hazardous nature of the chemicals combined with the method of application make any claim of savings questionable. The clear alternative to the hazards, risks and uncertainties of self-performing pickling is to bring in the experts.
The Risks Outweigh the Rewards
The main chemicals in pickling solutions are hydrofluoric acid (HF) and nitric acid (HNO3). The safety data sheets for these two highly corrosive chemicals detail the numerous risks of unprotected exposure to their vapors as well as physical contact. The most obvious and immediate is severe chemical burns to the skin and damage to the eyes and respiratory system just from the fumes. But with hydrofluoric acid, cumulative damage to the human body can continue undetected for years. This includes damage to internal organs and the development of osteoporosis in the bones.
According to their respective safety sheets, both hydrofluoric and nitric acids should only be used in well-ventilated areas. OSHA regulations further direct that anyone working with these acids should be wearing compatible personal protective gear including eye protection, gloves, respirators and protective coverings. Additionally, best practices state that eyewash and safety shower stations should be close at hand.
Quite often, the welded tubing will not be located in a well-ventilated location. As a result, the surrounding area will need to be off-limits to anyone not actively involved in the pickling process. If the front office workers can smell when the system is undergoing regular sanitization, it is not safe for them to be in the office while pickling is underway.
It is also worth considering that if pickling welds is not a common occurrence, how likely is it that the needed safety equipment works and meets requirements, or that the crew is current with the specialized training required to do the process safely and correctly? To put it bluntly, cutting corners can have consequences.
Environmental Concerns
Once the job is performed, the next question becomes, “what do you do with the waste?” The pickling chemistry will need to be rinsed from the location, but that residue cannot be flushed down the drain nor tossed in the trash. It must be treated as hazardous waste . That extends to any equipment that came in contact with the chemicals which will need to be cleaned or properly disposed of. Even if the acid is neutralized it can still be hazardous due to the heavy metals that may be pulled into the solution. Depending on the type and amount of acid involved, the waste removal process can be time consuming and costly. It’s important to carefully plan and execute the cleanup process to minimize the hazards and ensure it is done properly.
Did the Job Get Done Right?
Perhaps surprisingly, one of the biggest mistakes in self-performing pickling is the failure of the crews to rinse off the pickling paste. Naturally, this has implications for any product that comes in contact with the remaining acid and the above mentioned environmental hazards that present themselves when the contamination is discovered.
Another point of failure is when an inexperienced crew believes that the acids will also clean the surface of the metal. If the surfaces are not properly degreased, the acids may not be able to effectively penetrate and treat the stainless steel. In addition, if the surfaces are contaminated with grease, oil, or other inorganic compounds, these contaminants can interfere with the formation of the passive layer, potentially leading to the formation of rouge on the surface when the system is put back into operation.
Nonetheless, even if the area is properly degreased and cleaned beforehand and the acids are properly removed and disposed of, another point of failure lies in the assumption that pickling will restore the passive layer. The two are different processes with different results. The pickling paste will etch the metal and remove the discoloration, but the passive layer is damaged both from the actual weld and from the chemical action of the hydrofluoric acid in the pickling solution. To counter this, the usual practice is to apply nitric acid to the area to remove the free iron and make the surface chromium-rich, thus generating a stronger passive layer. However, nitric acid requires the same time and precautions to apply and then safely dispose of the resulting waste. Once completed, it is hard to judge the level of passivation achieved or whether it is consistent across the entire treated surface.
In some industries, this presents a problem because it is difficult to document that the area complies with the required ASTM standards. In the food and beverage industries or in systems that transport drinking water, any uncertainties over the safety and thoroughness of the pickling and passivation become more than just an academic question.
Leaving It to the Experts
Astro Pak has decades of experience treating welds on stainless steel. An analysis of your specific needs and industry standards will show whether the surface needs to be pickled first or if the scaling and heat discoloration can be addressed by even safer methods such as electrolytic weld cleaning (ELC) or electropolishing (EP). If pickling is required, Astro Pak’s technicians are fully trained, certified and equipped to perform the job safely and thoroughly. Additionally, they can safely handle any resulting hazardous material.
These processes should be followed up by a passivation treatment using Astro Pak’s patented Ultra Pass® Gel to ensure the maximum possible chromium-to-iron ratio in the stainless steel’s surface to create the most optimal passive layer. All of this will be tested and documented to show that the work conforms to the applicable ASTM standards.
Beyond the reduction in hazards and risks, using outside professionals may also result in cost savings compared to pickling welds in-house. Astro Pak possesses the required equipment, chemistry, and process to ensure that the job can be performed faster – and safer – leading to decreased downtime helping your bottom line. Your safety officer will also appreciate not having to store the hazardous materials nor manage the personal protective equipment required.
