TECH TALK
ASTM A350 Grade LF2 is a low temperature carbon steel suitable for lowest temperature of -46 ° C in piping systems when there is a possibility of process fluid temperature falling below -29 ° C during operation .
Stainless Steel Specifics
Among the forged steel grades mentioned , the ones covered in points 3 and 4 are stainless steels . Stainless steel is a group of ferrous alloys that contain a minimum of approximately 10 % -20 % chromium , a composition that prevents the iron from rusting , and provides heatresistant properties .
304 stainless steel is the most standard used alloy of this type . Essentially , 304 is an austenitic chromium alloy which is also known as an ‘ 18 / 8 ’ stainless as the make-up of the steel is 18 % chromium and 8 % nickel .
304L is an extra low-carbon variation of 304 stainless steel with a 0.03 % maximum carbon content , that eliminates carbide precipitation due to welding . As a result , this alloy has better weldability comparing to 304 stainless steel . It often eliminates the necessity of annealing weldments except for applications specifying stress relief . It also has slightly lower mechanical properties than 304 .
Grades 304 & 304L stainless steels have strong anti-rust and anti-corrosion performance , and show excellent resistance to a wide range of atmospheric , chemical , textile , petroleum , and food industry exposures . They are non-magnetic and non-hardenable , except by cold working , and are appropriate in field working applications , however are susceptible to chloride stress corrosion cracking .
The maximum temperature to which 304 stainless steel and 304L ball valves can be exposed continuously without appreciable scaling is about 1650 ° F ( 899 ° C ). For intermittent exposure , the maximum exposure temperature is about 1500 ° F ( 816 ° C ).
Grades 316 & 316L stainless steels are valve industry standard stainless steel body material . Comparing to 304 , the addition of molybdenum increases the general corrosion resistance , and the resistance to pitting by chlorides . It has the widest temperature range of any standard material : -425 ° F ( -254 ° C ) to 1500 ° F ( 816 ° C ). The alloys are used in mildly acidic and alkaline conditions and for handling citric , oxalic , and phosphoric acids .
F50 and F51 are duplex stainless grades , they are called duplex grades because their metallurgical structure consists of two phases : austenitic phase and ferritic phase . They are designed to provide better corrosion resistance , particularly chloride stress corrosion and chloride pitting corrosion , and higher strength than standard austenitic stainless steels such as Type 304 or 316 . The main differences in composition , when compared with an austenitic stainless steel , is that the duplex steels have a higher chromium content , 20 – 28 %; higher molybdenum , up to 5 %; lower nickel , up to 9 % and 0.05 – 0.50 % nitrogen . Both the low nickel content and the high strength ( enabling thinner sections to be used ) give significant cost benefits . They are therefore used extensively in the offshore oil & gas industry and petrochemical industry applications including valves . Duplex stainless steels also have greater toughness than ferritic alloys , especially at low temperatures .
F53 , F55 , F60 are super duplex stainless grades , which are high grades of duplex steels and have all of the good properties of the duplex steels . Comparing to the lower grades of duplex steels , super duplex steels have higher chromium and molybdenum content1 , which makes them extremely resistant to uniform corrosion by organic acids like formic and acetic acid . Super duplex also provides excellent resistance to inorganic acids , especially those containing chlorides .
ABOUT THE AUTHORS
Discussion
The materials mentioned in this article cover the most commonly used materials for industrial valves . In addition to them , for valve applications that handle non-corrosive fluids , at low pressure and room temperatures , cast iron is a very cost-effective option , and for very corrosive fluids , more exotic alloy grades higher than super-duplex stainless steels could be needed . To conclude , the decision needs to be made based on material-fluid compatibility .
REFERENCES
1 . ASTM B16.34-2020 Valves – Flanged , Threaded , and Welding End
2 . Norsok Standard – Design Principles , Material Selections , Rev . 1 , December 1994
Dongcheng Li is the inventor of two ball valve patents , and the designer of several other creative new valve features . He is the chief engineer and R & D manager at FBV Inc . Before joining the valve industry , he was a pipeline engineer and is the main force who engineered the unique energy efficient gas extraction process of the novel gas to power projects KivuWatt and Kivu56 in Rwanda , Africa .
Gobind N Khiani , a U Calgary alumnus of Masters in Mechanical Engineering is a seasoned change-maker . He has a proven track record in technical and value engineering and holds a Fellowship in Engineering and an MBA . He is the Task Force Lead of the End User Group at API609 and Vice Chairman of the Standards Council of Canada . He has done peer review on Emissions Management regulatory documents for ECCA / EPA and participated in research and development initiatives .
24 Valve World Americas | November 2024 • www . valve-world-americas . net