Hot or corrosive fluids flowing through pipes can eat away at the material, so much so that it becomes dangerous to anyone in the area. According to the US Department of Transportation, Pipeline & Hazardous Materials Safety Administration, data show that from 1998-2017 approximately 18% of pipeline incidents on average were caused by corrosion. Corrosion is considered a time-dependent threat which means it grows or worsens with time if left unmitigated. As a result, early detection and mitigation are necessary to minimize the impact of corrosion.
Carbon steel that contains too much residual nickel, copper and chrome in piping has been known to hinder protection against corrosive fluids and cause explosions. This article will address nickel-bearing carbon steels and the need for consistent Positive Material Identification (PMI) checks.
What is Carbon Steel Piping?
Carbon steel piping is primarily made of iron and carbon, with trace amounts of other elements such as manganese, sulfur, phosphorus, and silicon. The carbon content in carbon steel piping typically ranges from 0.05% to 2.0%, depending on the specific grade and application.
The presence of carbon gives carbon steel its characteristic strength and hardness. The higher the carbon content, the greater the strength and hardness of the steel. However, an excessively high carbon content can also make the steel more brittle.
Other elements present in carbon steel piping, such as silicon and manganese, help improve the strength, corrosion and heat resistance, and hardenability of the steel. Manganese also contributes to better weldability and formability. Sulfur and phosphorus are typically present in small amounts in carbon steel piping, as impurities from the raw materials and can have a detrimental effect on the weldability and ductility of the steel, so their content is usually minimized during steel production.
Adding Nickel to Carbon Steel
Some specialized grades of carbon steel, known as nickel-bearing carbon steels or nickel steel, contain a small percentage of nickel as an alloying element. These grades of carbon steel are specifically formulated to enhance certain properties, such as improved strength, toughness, and corrosion resistance. The addition of nickel in these specific grades of carbon steel allows for better resistance to corrosion and elevated temperatures compared to regular carbon steel.
There are some industries that are especially sensitive to corrosion and rely on nickel steel. For example, nickel carbon steel is utilized in oil and gas exploration, production, and refining processes where the piping or equipment is exposed to corrosive substances or high temperatures. Nickel carbon steel is also employed in chemical and petrochemical plants for handling corrosive chemicals, acids, and other aggressive fluids. A third major user of nickel carbon steel are power plants for components such as boilers, heat exchangers, and piping systems that are exposed to high pressures, temperatures, and corrosive environments.
The Effect of HF on Nickel Steel Piping
The proper selection, application and placement of the alloys within the process piping envelope is critical to avoid unexpected corrosion and deterioration of pressure equipment components. Case studies have shown that residual elements in carbon steel can contribute to accelerated HF corrosion, primarily chromium, nickel and copper elements.
Hydrofluoric acid (HF) Alkylation is an increasingly central process in the refining industry for the production of petrochemical products. It is a chemical process used to produce high-octane gasoline components. It involves the reaction of hydrocarbons with isobutane in the presence of hydrofluoric acid as a catalyst. That hydrofluoric acid is a highly corrosive and toxic substance, requiring strict safety precautions and specialized equipment for handling and containment.
The use of hydrofluoric acid in the alkylation process necessitates stringent safety measures to protect workers, the environment, and surrounding communities. One of those safety measures is a Positive Material Identification (PMI) program that includes checking the nickel content in carbon steel piping because too much or too little nickel can have significant implications on the performance and durability of the piping system. The desired steel alloy formula when dealing with HF is:
Nickel (Ni) + Copper (Cu) + Chromium (Cr) < 0.15%.
The Power of Positive Material Identification (PMI)
Checking the nickel content helps ensure that the material meets the required specifications and safeguard the long-term reliability and safety of the piping system, minimizing the risk of corrosion-related failures and associated maintenance costs.
Handheld XRF analyzers are crucial instruments to PMI analysis as they provide accurate elemental identification of all types of metal and alloys — from trace levels to major elements — and differentiate alloy grades that are nearly identical in composition.
X-ray fluorescence spectroscopy is a non-destructive analytical technique used to determine the elemental composition of materials. Handheld XRF analyzers work by measuring the fluorescent (or secondary) X-rays emitted from a sample when excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic fluorescent X-rays, or “unique fingerprints”. These “fingerprints” are distinct for each element, making handheld XRF analysis an excellent tool for quantitative and qualitative measurements.
With the press of a trigger of a handheld XRF analyzer, PMI specialists can quickly ascertain that important nickel-copper-chromium percentage. (You can watch our subject matter expert demonstrate low nickel detection for PMI using a handheld XRF analyzer in this 2-minute video.)
By checking the nickel content in carbon steel piping, it is possible to ensure that the material meets the required specifications and standards for the intended application. This helps to ensure the long-term reliability and safety of the piping system, minimizing the risk of corrosion-related failures and associated costs.
Additional Resources
- Video: Low Nickel Detection For PMI Using A Handheld XRF Analyzer
- Website: Portable Power Generation / Oil and Gas (PMI) Solutions
- Website: Handheld XRF and LIB analyzers for PMI
- Application Note: Rapid analysis of residual elements in carbon steel piping from hydrofluoric acid alkylation units
- eBook: XRF in the field: XRF technology for the non-scientist
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