[ Petrochemical ]
[ Petrochemical ]
paint for equipment and human safety are commonly used .
The role of stainless steel The presence of at least 10.5 % Cr in stainless steel creates a passive layer of chromium oxide , providing effective corrosion resistance . The other alloying elements in stainless steel improve corrosion resistance in other mediums , such as in marine environments , which are of concern in the oil and gas industry . In the refining process , oil extraction is done through high-pressure tubing and then collected in a separator vessel . Extracted crude oil is then transported via pipeline . The whole process is quite challenging ; hence , high-grade material is important for equipment and machinery to enhance sustainability .
Material selection Material selection has a significant impact on the operability , economics , and reliability of petrochemical refinery plants . Considerations for material selection include design , construction material , fabrication quality , operating conditions , maintenance practices , and environmental factors . Stainless steel AISI 304 or 316 , duplex and Precipitation Hardening grades are most suitable for manufacturing process equipment .
Fabrication of stainless equipment Stainless steel can be fabricated using any of the traditional forming and shaping processes . Rolled austenitic stainless steel as plate / sheet , spun or welded or seamless tube / pipe , hot or cold forged valves , and fittings are common products for manufacturing refinery equipment . Austenitic stainless steel is most commonly used for fabrication in shape as per design . Austenitics can be cold-worked to improve hardness , strength , and stress resistance . It can also be heated to be shaped , but returns to its original strength when cooled . Stainless steel / plate is a highly weldable material , and a welded joint can provide optimum corrosion resistance , strength , and fabrication economy . The welding process for stainless steel varies depending on the thickness ; three common welding processes are resistance welding , MIG and TIG .
Typical types of corrosion Uniform corrosion - Typical causes of corrosion are exposure to corrosive chemicals in the equipment ,
Chemical composition (%) of popular stainless steel used to manufacture equipment .
Type C Mn Si S P Cr Ni Mo
304 0.08max 2.0max 0.75max 0.03max 0.045max 18-20 8-10.5 – 316 0.08max 2.0max o . 75max 0.03max 0.045max 16-18 10-14 2-3
Mechanical properties
Type Tensile strength Yield strength Hardness Elongation Liquidus Solidus 304 505MPa 205MPa 123 BHN 70 % 1450 ° C 1400 ° C 316 480MPa 170MPa 149 BHN 40 % 1400 ° C 1370 ° C
For pitting corrosion protection AISI 316 ( Moly bearing ), performs better than the common18 / 8 , 304 .
Sensitive and corrosion-prone equipment such as valves , storage tanks , etc ., that are exposed to medium to high temperatures should be constructed from stainless steel .
surroundings and environment , and poor aeration . It is also more common in steels with unwanted inclusions or manufacturing defects . For example , manganese-sulphide manganese often initiates pitting . Adequate oxygen availability may help to reduce the rate of pitting corrosion or halt it entirely , depending on the cause . The molybdenum in stainless steel increases its ability to resist pitting corrosion . Other considerations include pH , chloride concentration and the temperature of the environment in which the products are exposed . Crevice corrosion - Occurs when a crevice between the stainless steel and another material allows chloride compound to concentrate or prevents proper oxygen levels to regenerate the oxide layer formed and typically found near or within the gap between two metals . Crevice corrosion can also occur between metallic and non-metallic surfaces . Weld decay corrosion - Occurs in petroleum refineries in very large joints in pipelines or tanks . Localised corrosion takes place as preferential weld corrosion . This is the result of damage in weld joints where a galvanic couple is established between the parent pipe and the weld in the heat affected zone ( HAZ ), or the weld metal , due to the different chemical composition of welding rods . Welding in pipelines , tanks etc . is a critical process where metal components are combined
52 Stainless Steel World June 2024 www . stainless-steel-world . net