Materials engineers cannot afford to leave anything to chance – especially in the realms of industrial safety and quality control. It matters even more in the high-stakes arenas of oil & gas facilities or power plants, where the integrity of materials can mean the difference between smooth operations and catastrophic failure.
Robust material testing is not just a prerequisite but an ongoing obligation for industrial safety engineers. Initial material verification is often followed up by spot testing of subassemblies, yet this approach is fraught with inaccuracies. A better solution is to deploy positive material identification (PMI) tests using portable chemical analysis solutions, preferably handhelds which enable users to safely perform verifications in challenging environments and hard-to-reach areas.
PMI tests are procedures used to verify the chemical composition of metals and alloys. They are crucial in industries where the correct material grade and composition can significantly impact safety and performance. Additionally, PMI tests are crucial in testing the effects of dynamic processes on components and substructures in the field. This latter approach requires a highly portable solution, hence the growing importance of handheld X-ray fluorescence (HHXRF) and laser-induced breakdown spectroscopy (LIBS) analyzers.
Now, let’s delve into five different PMI tests that play a pivotal role in these industries.
1. Carbon Equivalency (CE)
Carbon equivalency is a PMI test that predicts the heat-affected zone (HAZ) hardenability in steel. The weldability of steel is primarily influenced by its carbon content, and the presence of other elements such as manganese, chromium, molybdenum, vanadium, copper, nickel, and silicon also affects its carbon equivalence (CE). When hardness is increased with greater amounts of carbon and other elements, weldability decreases. In welding specifically, CE calculations are used to predict the heat-affected zone (HAZ) hardenability, which in turn helps determine the compatibility of materials being joined together by fillers.
2. Sulfidic Corrosion
Naturally occurring sulfur compounds in crude oil make corrosion testing crucial in the oil and gas industry. This PMI test identifies the susceptibility of a material to sulfidic corrosion, which can lead to equipment failure such as the thinning of piping walls and equipment. Sulfidic corrosion affects all components in piping systems, including fittings, heater tubes, and pressure vessels. The rate of corrosive thinning depends on factors such as the sulfur content of the oil, operating temperatures, flow rate, and H2 concentration, making it difficult to predict accurately.
3. HF Alkylation
HF alkylation testing is used to identify materials resistant to corrosion in hydrofluoric acid environments. This is particularly important in oil refining processes where hydrofluoric acid is used. However, HF alkylation units can be susceptible to corrosion issues, which can affect the safety and reliability of the process. Corrosion in HF alkylation units is closely linked to feed quality and operating conditions. Carbon steel, which is commonly used in HF alkylation units, is known to be susceptible to hydrofluoric acid corrosion. Corrosion can lead to the formation of fine particles of iron fluoride scale that eventually spall off from the equipment and contribute to fouling.
4. Flow Accelerated Corrosion (FAC)
Flow accelerated corrosion testing is a PMI test used to identify materials susceptible to corrosion due to the flow of fluids. Flow-accelerated corrosion (FAC) is a type of corrosion mechanism that occurs when a normally protective oxide layer on a metal surface dissolves in fast-flowing water or steam. The underlying metal corrodes to recreate the oxide, and thus the metal loss continues. FAC is primarily an electrochemical corrosion process aided by chemical dissolution and mass transfer. The rate of FAC depends on the flow velocity, and it often affects carbon steel piping carrying ultra-pure, deoxygenated water or wet steam. Stainless steel does not suffer from FAC, and FAC of carbon steel halts in the presence of small amounts of oxygen dissolved in water. FAC rates rapidly decrease with increasing water pH.
5. Microalloying Elements
Testing for microalloying elements is a PMI test that identifies the presence of small amounts of alloying elements. Microalloyed steels, often referred to as high-strength low-alloy steels (HSLA), are a family of materials strengthened by the addition of “micro” alloy concentrations to low-carbon steel (also called mild steel). The technology of microalloying includes adding specific elements to achieve desired mechanical properties. The strengthening effects of these elements make microalloyed steels particularly suited for high-strength applications, but microalloying can also detract from desired qualities such as toughness, ductility, and weldability.
Real-World Impact of Handheld PMI Testing
Handheld analyzers are redefining PMI testing through their accuracy and convenience. They are compact and ergonomic, allowing for material verification at heights, offshore, or while navigating through pipe racks. Corners, joints, and tight welds can be readily analyzed, ensuring no detail is overlooked. Refer to our positive material identification page for more information on the benefits of deploying handheld analyzers for PMI testing in power generation and oil and gas.
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