Design & Fabrication Resources
Design and fabrication resources for chemical process equipment designers, fabricators, and manufacturers:
Gasket Design Criteria
The Gasket: A gasket is a compressible material, or a combination of materials, which when clamped between two stationary members prevents the passage of the media across those members. The gasket material selected must be capable of sealing mating surfaces, resistant to the medium being sealed, and able to withstand the application temperatures and pressures.
How Does It Work? A seal is effected by the action of force upon the gasket surface. This force which com- presses the gasket, causes it to flow into the flange macro and micro imperfections. The combination of contact stress, generated by the applied force between the gasket and the flange, and the densification of the gasket material, prevents the escape of the confined fluid from the assembly.
How to Weld Type 2205 Code Plus Two® Duplex Stainless Steel
2205 is a duplex (austenitic-ferritic) stainless steel that combines many of the best properties of austenitic and ferritic stainless steels. High chromium and molybdenum contents provide excellent resistance to pitting and crevice corrosion. The duplex structure is highly resistant to chloride stress corrosion cracking. 2205 has outstanding strength and toughness and possesses good weldability. The trademark Code Plus Two® indicates the commitment, not only to meet the requirements for S31803 as established in ASTM and ASME, but also to meet two additional requirements.
The first requirement was that nitrogen should be in the 0.14 to 0.20% range to gain its benefits in higher strength, higher corrosion resistance, greater metallurgical stability, and superior properties after welding. The second requirement was that all mill products should pass a test for the absence of detrimental intermetallic phases. The tests developed by Outokumpu Stainless for this purpose have been formalized as the ASTM A 923 standard test method.
Practical Guidelines for the Fabrication of Duplex Stainless Steels
Duplex stainless steels are a family of grades combining good corrosion resistance with high strength and ease of fabrication. Their physical properties are between those of the austenitic and ferritic stainless steels but tend to be closer to those of the ferritics and to carbon steel. The chloride pitting and crevice corrosion resistance of the duplex stainless steels are a function of chromium, molybdenum, tungsten, and nitrogen content. They may be similar to those of Type 316 or range above that of the sea water stainless steels such as the 6% Mo austenitic stainless steels.
All duplex stainless steels have chloride stress corrosion cracking resistance significantly greater than that of the 300- series austenitic stainless steels. They all provide significantly greater strength than the austenitic grades while exhibiting good ductility and toughness.
Practical Guidelines for the Fabrication of High Performance Austenitic Stainless Steels
In recent years, new highly corrosion-resistant austenitic stainless steels have entered the market- place. They have demonstrated cost-effective performance in a variety of harsh and corrosive environments. They have supplied the materials engineer with alloys for demanding new energy and environmental needs. These new materials are called “High Performance Austenitic Stainless Steels” (HPASS). They obtain their performance through alloying with higher than usual amounts of molybdenum and nitrogen. They are more complex than the standard stainless steels, and demand that engineers, designers, and fabricators have thorough knowledge of their characteristics in order to specify and fabricate them successfully. This brochure provides basic information on HPASS grades and compares them to the standard grades. Its primary focus is to compare the fabrication characteristics of the two groups of steels, and to identify similarities and differences between them. This information will help those responsible for fabricating HPASS to manufacture a high-quality product that will perform successfully in the field.
Welding Titanium and its Alloys
Titanium is a reactive metal; it will burn in pure oxygen at 600°C and in nitrogen at around 800°C. Oxygen and nitrogen will also diffuse into titanium at temperatures above 400°C raising the tensile strength but embrittling the metal. In the form of a powder or metal shavings titanium also constitutes a fire hazard.
Because of the affinity of titanium and its alloys for oxygen, nitrogen and hydrogen and the subsequent embrittlement, fluxed welding processes are not recommended although they have been used, primarily in the former USSR. Arc welding is therefore restricted to the gas shielded processes (TIG, MIG and plasma-TIG) although power beams, the solid phase processes and resistance welding are also used.
Titanium is allotropic; it has two different crystallographic forms depending on the temperature and chemical composition. Below 880°C it forms the hexagonal close packed alpha phase, above 880°C it exists as body centered cubic beta phase.
The Use of 2205 Duplex Stainless Steel for Pharmaceutical and Biotechnology Applications
The hygienic requirements for the pharmaceutical and biotechnology industries are relatively high and the materials of construction for processing vessels and piping systems must demonstrate outstanding corrosion resistance and cleanability to ensure the purity and integrity of the drug product. Materials must be capable of withstanding the temperature, pressure, and corrosive nature of the production environments as well as all sanitizing and cleaning procedures. In addition, candidate materials must have good weldability and must be capable of meeting the industry’s surface finish requirements.
Type 316L stainless steel has a microstructure that consists of austenite phase and a very small volume of ferrite phase. This is achieved primarily by adding sufficient nickel to the alloy to stabilize the austenite phase. The nickel content of wrought 316L stainless steels is typically in the range of 10–11%. Duplex stainless steels have a chemical composition that is adjusted to produce a microstructure that consists of approximately equal parts ferrite and austenite phases (Figure 2).
ZERON 100® Fabrication
ZERON 100 was the first of the super duplex stainless steels. Its unique chemical composition has been shown to be correctly balanced to offer the best combination of corrosion resistance and strength. The steel is tightly controlled from melting through manufacture to ensure better and consistent performance than the same generic grade.
ZERON® 100 is a super duplex stainless steel for use in aggressive environments. ZERON 100 offers strength levels exceeding that of standard duplex grades like 2205. ZERON 100 is resistant to corrosion in a wide range of organic and inorganic acids. The copper content gives excellent resistance to corrosion in many non-oxidizing acids. This alloy is also resistant to strong alkalis. ZERON 100 is not recommended for uses which involve extended exposure to temperatures greater than 600°F as this causes a substantial reduction in toughness. ZERON 100 is welded using ZERON 100X filler metal.
ZERON 100X grade welding consumable is overalloyed with nickel and is intended for joints that are to be put into service in the as-welded condition. ER 2594 (AWS A5.9), E 2594-15 (AWS A5.4)
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