What to know when working with corrosive liquids
A corrosive liquid is a fluid that attacks and destroys materials with which it comes into contact. Metals, stone, glass, and even some types of plastics can be susceptible to corrosion by corrosive liquids or chemicals, which fall into six categories: strong acids, weak acids, strong bases, weak bases, desiccants and oxidizing agents. Some chemicals may belong to more than one category. For example, sulfuric acid is a strong acid, desiccant and oxidant. Corrosives can also belong to other hazard categories such as toxicity (toxic) or flammability.
While corrosive liquids can destroy materials like glass and metal, they are obviously dangerous to humans. The U.S. Occupational Safety and Health Administration (OSHA) recognizes the health risks posed by these substances, defining them as “a chemical that produces destruction of skin tissue, namely visible necrosis through the epidermis and in the dermis, in at least one of the three animals tested after an exposure of up to four hours.Corrosive reactions are characterized by ulcers, bleeding, bloody scabs and, after 14 days of observation , discoloration due to whitening of the skin, complete areas of alopecia and scarring.
When a pump is used to transfer hazardous liquids in oil and gas dehydration, such as flammable, combustible, toxic and corrosive chemicals, it is essential that several factors are considered. These considerations are key to choosing the right pump for the job.
First, the characteristics of the fluid. What type of fluid will be pumped? What are the characteristics of this fluid? This information can be found in the Fluid Safety Data Sheet (SDS, formerly known as Material Safety Data Sheet or MSDS).
According to an OSHA summary of the SDS, “HCS 29 CFR 1910.1200(g) requires the manufacturer, distributor, or importer of chemicals to provide SDSs for each hazardous chemical to downstream users to communicate information on these dangers… such as the properties of each chemical product; physical, sanitary and environmental health risks; Protective measures; and safety precautions for handling, storage and transportation of the chemical. The fluid SDS provides critical data such as concentration, specific gravity, temperature resistance, viscosity, flammability (if applicable) and solids content specifics.
To ensure that the pump is properly sized, users should also consider the pump manufacturer’s load capacity curve. A pump curve (also called a pump selection curve, pump efficiency curve, or pump performance curve) provides the information needed to determine a pump’s ability to produce flow under the conditions that affect pump performance. the machine.
Reading pump curves accurately – or consulting a pump professional who can – ensures users get the right pump based on application variables such as: head (such as the energy required to evacuate water from a pump at an equivalent height expressed in feet or meters); flow rate (the volume of liquid to be moved in a given period of time, i.e. gallons per minute [gpm] or cubic meters per hour [m3/h]); rotations per minute (rpm); impeller size, depending on pump performance; Powerful; Efficiency; and the Net Positive Suction Head (NPSH).
The right pump for an application
The most commonly used equipment for transferring corrosive petroleum and gaseous fluids is the centrifugal pump. Centrifugal pumps are energy efficient, available in standard flooded suction or self-priming, and come in a wide range of sizes designed to pump from a few gpm to thousands of gpm.
When pumping corrosive liquids, centrifugal pumps offer another advantage: mechanical seals. These seals will prevent leaks where the internal rotating shaft protrudes from the stationary pump housing. This is similar to how an automobile’s water pump uses a mechanical seal to prevent coolant leaking from the pump. A mechanical seal uses carefully machined flat rings of a durable material, such as carbon ceramic or silicon carbide, where one rotates with the shaft and the other is stationary. The pumped fluid moves between the seal faces and forms a lubricating film. If the pump is run without liquid (dry running), the friction causes the sealing faces to heat up rapidly, leading to seal failure.
If a mechanical seal fails as a result of dry running, liquid will leak from the pump. If the pumped liquid is water, this may only be an inconvenience. With corrosive fluids, a leak can cause harm to humans, potentially causing significant damage to surrounding infrastructure and possibly creating an environment in which users are no longer in compliance with regulatory agencies, such as OSHA . Additionally, there are downtime and cost (or mean time between failure) considerations. [MTBF]) when a pump needs to be taken out of service and repaired.
Suitable building materials
It is important to choose the correct pump materials of construction. This is especially critical when moving corrosive liquids. Failure to do so will cause corrosion of components that encounter the corrosive fluid, such as seals and O-rings, which can impact both pump performance and service life.
According to corrosionpedia.com, corrosion is defined as “the deterioration and loss of a material and its critical properties due to chemical, electrochemical and other reactions of the exposed surface of the material with the surrounding environment. Corrosion of metals and of nonmetals occurs due to gradual environmental interaction at the surface of the material.
Now, corrosion by itself is usually not that big of a problem. Suitable materials of construction, such as cast iron, bronze, manganese bronze, nickel-aluminum bronze, cast steel, and stainless steel, are readily available and capable of handling most corrosive fluids safely and efficient. It is important to understand the different types of corrosion, as well as the factors that contribute to the rate of corrosion, to select the appropriate materials.
It can be difficult to choose a material that can resist corrosion and additional factors, such as erosion and cavitation. A general rule of thumb in selecting suitable materials of construction is to first select materials that will resist corrosion, then select one that provides the most appropriate resistance to abrasion and/or cavitation. Here are some examples of corrosion users may encounter when using a centrifugal pump to move corrosive fluids.
Abrasion, or abrasive wear, is the removal of metal caused by the mechanical action of cutting or abrading solids conveyed in a pumped liquid. When the corrosive liquid being pumped also contains abrasive solids (abrasion-corrosion), high-alloy materials such as stainless steel are often required to ensure pump performance and life. In centrifugal pumps, the impeller is particularly sensitive. Although the housing can be damaged by this, the biggest problem is usually the impeller, along with the wear rings.
Most commonly occurring with high suction energy pumps, cavitation is the removal of metal due to high, localized stresses produced on the metal surface by the implosion of cavitation vapor bubbles. In an abrasive and corrosive cavitation environment, the base material is eroded as the abrasive particles are accelerated towards the surface of the wheel by the implosive force of the cavitation bubbles, accelerating the corrosion process.
Consult a professional
Although this is not a complete guide to pump selection when transferring corrosive fluids, we hope it provides users with an overview of the challenges, as well as some of the critical factors to consider when choosing a pump. There’s a lot to consider, from the type of fluid being transported to selecting the proper pump materials of construction.
Users should begin by gathering information about the fluid to be pumped. Second, gather information about application requirements and environmental conditions. Then consult a pump professional who can advise you on choosing the right pump for the job taking into account all of the above factors.