Pipes can be divided into metal pipes and non-metal pipes.Metal pipes are further subdivided into ferrous and non-ferrous types.Ferrous metals are mainly composed of iron, while non-ferrous metals are not composed of iron.Carbon steel pipes, stainless steel pipes, chrome molybdenum pipes and cast iron pipes are all ferrous metal pipes with iron as the main component.Nickel and nickel alloy pipes, as well as copper pipes, are non-ferrous pipes.Plastic pipes, concrete pipes, plastic-lined pipes, glass-lined pipes, concrete-lined pipes and other special pipes that can be used for special purposes are called non-metallic pipes.Ferrous metal pipes are the most widely used pipes in the energy industry; carbon steel pipes are used extensively.ASTM and ASME standards govern a variety of pipes and piping materials used in the process industry.
Carbon steel is the most used steel in industry, accounting for more than 90% of total steel production.Based on carbon content, carbon steels are further divided into three categories:
In alloyed steels, different proportions of alloying elements are used to achieve desired (improved) properties such as weldability, ductility, machinability, strength, hardenability and corrosion resistance, etc.Some of the most commonly used alloying elements and their roles are as follows:
Stainless steel is an alloy steel with a chromium content of 10.5% (minimum).Stainless steel exhibits extraordinary corrosion resistance due to the formation of a very thin Cr2O3 layer on the surface.This layer is also known as the passive layer.Increasing the amount of chromium will further improve the corrosion resistance of the material.In addition to chromium, nickel and molybdenum are added to impart desired (or improved) properties.Stainless steel also contains varying amounts of carbon, silicon and manganese.Stainless steel is further classified as:
In addition to the above grades, some advanced grades (or special grades) stainless steels also used in the industry are:
Tool steels have a high carbon content (0.5% to 1.5%).Higher carbon content provides higher hardness and strength.This steel is mainly used to make tools and molds.Tool steels contain varying amounts of tungsten, cobalt, molybdenum and vanadium to increase the metal’s heat and wear resistance as well as durability.This makes tool steel ideal for cutting and drilling tools.
These pipes are widely used in the process industry.ASTM and ASME designations for pipes look different, but the material grades are the same.E.g:
The material composition and properties on the ASME and ASTM codes are identical except for the name.The tensile strength of ASTM A 106 Gr A is 330 Mpa, ASTM A 106 Gr B is 415 Mpa, and ASTM A 106 Gr C is 485 Mpa.The most commonly used carbon steel pipe is ASTM A 106 Gr B.There is an alternative to ASTM A 106 Gr A 330 Mpa, ASTM A 53 (Hot Dip Galvanized or Line Pipe), which is also a widely used grade in carbon steel pipe for pipe.ASTM A 53 pipe is available in two grades:
ASTM A 53 Pipe is divided into three types – Type E (ERW – Resistance Welded), Type F (Furnace and Butt Welded), Type S (Seamless).In Type E, both ASTM A 53 Gr A and ASTM A 53 Gr B are available.In Type F, only ASTM A 53 Gr A is available, while in Type S, ASTM A 53 Gr A and ASTM A 53 Gr B are also available.The tensile strength of ASTM A 53 Gr A pipe is similar to ASTM A 106 Gr A at 330 Mpa.The tensile strength of ASTM A 53 Gr B pipe is similar to ASTM A 106 Gr B at 415 Mpa.This covers carbon steel grade pipes that are widely used in the process industry.
The most used stainless steel pipes in the processing industry are called austenitic stainless steels.The essential characteristic of austenitic stainless steel is that it is non-magnetic or paramagnetic.Three important specifications for austenitic stainless steels are:
There are 18 grades in this specification, of which 304 L is the most commonly used.A popular category is 316 L because of its high corrosion resistance.ASTM A 312 (ASME SA 312) for pipes 8 inches or less in diameter.The “L” along with the grade indicates that it has a low carbon content, which improves the weldability of the pipe grade.
This specification applies to large diameter welded pipes.The piping schedules covered in this specification are Schedule 5S and Schedule 10.
Weldability of Austenitic Stainless Steels – Austenitic stainless steels have higher thermal expansion than ferritic or martensitic stainless steels.Due to the high coefficient of thermal expansion and low thermal conductivity of austenitic stainless steel, deformation or warpage can occur during welding.Austenitic stainless steel is prone to solidification and liquefaction cracking.Therefore, due care must be taken when selecting filler materials and welding processes.Submerged arc welding (SAW) is not recommended when fully austenitic stainless steel or low ferrite content welds are required.The table (Appendix-1) is a guide for selecting the appropriate filler wire or electrode based on the base material (for austenitic stainless steels).
Chromium molybdenum tubing is suitable for high temperature service lines because the tensile strength of chrome molybdenum tubing remains unchanged during high temperatures.The tube finds application in power plants, heat exchangers, and the like.The tube is ASTM A 335 in several grades:
Cast iron pipes are used for firefighting, drainage, sewage, heavy duty (under heavy duty) – underground plumbing and other services.The grades of cast iron pipes are:
Ductile iron pipes are used in underground piping for fire services.Dürr pipes are hard due to the presence of silicon.These pipes are used for commercial acid service, as the grade shows resistance to commercial acid, and for water treatment that discharges acid waste.
Nirmal Surendran Menon received a Bachelor of Mechanical Engineering from Anna University, Tamil Nadu, India in 2005 and a Master of Science in Project Management from the National University of Singapore in 2010.He is in the oil/gas/petrochemical industry.He is currently working as a field engineer on an LNG liquefaction project in southwest Louisiana.As part of project execution, his interests include piping system cleaning and loss prevention for LNG liquefaction facilities.
Ashish holds a bachelor’s degree in engineering and has over 20 years of extensive involvement in engineering, quality assurance/quality control, supplier qualification/monitoring, procurement, inspection resource planning, welding, fabrication, construction and subcontracting.
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