Welding Alloys for Petrochemical Applications: Selecting the Right Materials for the Job
The petrochemical industry relies on a significant number of highly exotic alloys for the efficient and safe operation of pressure vessels, process piping, and other equipment. The processing and storage units in petrochemical facilities undergo extreme temperature and pressure swings. So, the petrochemical equipment is made from alloys with particular characteristics that enable it to endure corrosive agents and high temperatures.
It’s paramount to choose a suitable welding filler metal alloy for every part of the petrochemical facility. A wrong welding alloy selection can cause a high capital loss, especially if applied to a large number of welds.
Most Commonly Used Welding Alloys In Petrochemical Applications
Depending on the petrochemical end product, a plant can have different kinds of equipment made from various alloys. But, the majority of the exotic alloys used for petrochemical applications are low alloy steels, like creep resistant steel, nickel base alloys, and stainless steels. These materials are often susceptible to weld alloy selection. Choosing inadequate filler metals can lead to significantly weaker welds than the base metal or corrosion susceptibility from aggressive chemicals.
Stainless steels like austenitic 304 and 316L, duplex, and super duplex alloys are used extensively to fabricate chemical tankers, process piping, heat exchangers, and pressure vessels. The list of stainless steel applications in the petrochemical plants is inexhaustible. This material is one of the cornerstones of the petrochemical industry, as the majority of the processing equipment relies on it to endure highly corrosive agents.
Stainless steels resist corrosion when exposed to various sulfur compounds, making them an excellent choice for many petroleum refining processes. However, alloys are designed to answer different challenges. For example, the 316 stainless steel has the addition of molybdenum to offer superior resistance to chlorides and reducing acids. If the operating conditions are more severe, duplex or super duplex stainless steels can provide additional corrosion resistance. In addition, stainless steels have high strength, excellent fabrication characteristics, and require low maintenance.
However, stainless steel is sensitive to prolonged high temperature exposure, such as welding. It can undergo the carbide precipitation process, which leads to intergranular corrosion and the loss of corrosion-resistant properties in the weld and heat affected zone (HAZ). Therefore, heat input control is vital for high quality stainless steel welds. It’s recommended to apply advanced welding processes to reduce heat input when welding austenitic stainless steels. For example, regulated metal deposition (RMD) and Pulsed MIG, available from the Miller Pipeworx 400 or EX360 FieldPro multi-process welders. Another excellent advanced process to reduce heat input is surface tension transfer (STT) from Lincoln Electric, offered by welders like the Power Wave 455M.
Stainless steel alloys used in the petrochemical industry are highly diverse and often specialized. Therefore, it’s vital to choose welding consumables designed for the welded alloy. The filler metal alloy selection also influences the weld joint characteristics. However, generally, stainless steel welding alloys should match the alloy of the base metal or exceed it in alloy content if the matching electrodes aren’t available on the market. For example, 304 stainless steel can be welded with a 308 filler metal, while you can use 309 or 316 to weld the 309 stainless steel.
Nickel Based Alloys
Nickel based alloys are highly specialized and designed to provide exceptional corrosion resistance. But, nickel alloys have a special edge for petrochemical applications. They have a high creep resistance, which means that they can endure continuous stresses at high temperatures. As a result, nickel alloys are used for pipes, tubes, heat boilers, catalyst tubes, distillation towers, pumps and valves, pigtails, heat exchangers, condensers, and many other specialized equipment where high corrosion resistance and mechanical properties at elevated temperatures are paramount.
The most commonly applied nickel alloys in the petrochemical industry are Inconel, Incoloy, Hastelloy, and Monel alloys. The alloy selection depends on the operating conditions, welding variables, and economic constraints. However, petrochemical plants usually need numerous nickel alloys for various processing equipment.
Nickel alloys are typically welded with matching or near-matching filler metal alloys. However, using nickel-copper alloy to weld the matching base metal in some environments may lead to galvanic corrosion. In such cases, it’s crucial to conduct on-site evaluation weld tests with non-matching welding alloys before any critical welding equipment is welded with them.
Low Alloy Steels
Low alloy steels play a major role in petrochemical facilities. Whenever an application requires high strength materials with high corrosion, hydrogen, and temperature resistance, low alloy steels are often the best choice.
CrMo and CrMo(V) Low Alloy Steels
The best example of low alloy steels are the CrMo low alloy steels, with their long history in the petrochemical industry. CrMo steels are high temperature and creep resistant. They are most commonly used for the production of heaters, boilers, reactors, hydrocrackers, and heavy wall pressure vessels. CrMo steels are usually welded with matching weld alloys to achieve a homogeneous joint with equal weld properties.
As the petrochemical and power generation industries kept pushing the envelope of what’s possible to meet ever-increasing stringent requirements, the demand for increased properties of CrMo steels kept growing. As a result, advanced CrMo steels have been developed, like the CrMo(V) steel with the addition of vanadium. The vanadium-enhanced CrMo(V) steels offer increased performance and strength but require highly stringent welding procedures and specialized welding consumables. These steels are more sensitive to weld cracking and heat input, making the welding process challenging and precise heat control paramount.
Low Alloy Ni Cryogenic Steels
Another example of commonly used low alloy steels are cryogenic nickel alloyed steels. The nickel content in these steels ranges from 1.5 to 9%, allowing them to endure severe subzero temperatures. Cryogenic steels are used for fabrication of equipment in petrochemical facilities and the oil and gas industry for handling and storage of liquefied petroleum gases (LPG) and production and handling of gases like oxygen, ammonia, ethylene, and carbon dioxide. Depending on the nickel content, these steels can be subjected to service temperatures as low as -320°F (-196°C). Unlike many other steels, cryogenic steels don’t become brittle under extreme subzero temperatures, making them a safe material for petrochemical processing and storage.
Choosing a consumable for nickel alloyed cryogenic steels is a challenging task, especially for 9% nickel alloyed steel. High nickel consumables are expensive. So, selecting the correct electrodes comes down to the required tensile strength of the weld, the minimum operating temperature, and economic constraints.
Rent Or Lease Welding Equipment From Red-D-Arc
Red-D-Arc can help you meet your welding and cutting equipment needs for petrochemical contracting. Our massive fleet of advanced welding and cutting power sources and weld automation equipment can help you take on more jobs without investing in costly equipment. By renting our welders and other equipment, you can immediately experience the ROI and scale in and out of the job once complete.
Contact us today, and our team of experts will help you choose the most suitable welding equipment for your next petrochemical maintenance, repair, or installation job. Whether you are working on massive pressure vessels or need to conduct welding maintenance of the entire petrochemical plant, we have the tools to improve your productivity and bottom line.
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