Performance of ferritic steel 16MnDR using improved local fracture criterion

Based on the finite element analysis and fracture toughness test data, this paper verifies the improved Ritchie-Knott-Rice (RKR) local failure criterion using 16MnDR ferritic steel for cryogenic pressure vessels. This criterion's applicability to 16MnDR was verified to verify fracture toughness's different influence factors in the ductile-to-brittle transition temperature (DBTT) region, such as specimen thickness (TST) and temperature. The results indicate that the (4δt, σ22c) criterion applies to 16MnDR steel and effectively transfers the minimum Jc value between samples of different temperatures and thickness.

A Reaffirmation of Fracture Toughness Requirements for ASME Section VIII Vessels for Service Temperatures Colder Than 77 K

To assure adequate fracture resistance of cryogenic pressure vessels designed to operate at a minimum design metal temperature (MDMT) colder than 77 K (−196 °C or −320 °F), current American Society of Mechanical Engineers (ASME) Code, Section VIII, Division 1, UHA-51 Impact Test rule requires that the weld metal (WM) meets or exceeds 0.53 mm (21 mils) lateral expansion at 77 K, i.e., LE77K ≥ 0.53 mm (21 mils), as determined using Charpy V-notch (CVN) impact testing. To the credit of this rule, cryogenic pressure vessels fabricated to date meeting the above requirement had continued to serve well—without any adverse incident—in numerous applications across the world, at cryogenic temperatures colder than 77 K. However, a critical examination of the underlying research which relied on a regression equation relating ratio of fracture toughness to yield strength obtained at 4 K, i.e., [KIc/YS]4K with LE77K, revealed that the technical basis for establishing the above requirement is metallurgically unsustainable. To successfully overcome this, the present research employed dimensional analysis and balancing of the previously published regression equations and proposed [KIc/YS]277K as a valid fracture resistance parameter applicable for MDMT 77 K and warmer, as well as MDMT colder than 77 K. Related efforts offered equivalent fracture resistance as an insightful concept, wherein the minimum fracture resistance parameter for a MDMT colder than 77 K is equated as a simple multiple of the minimum fracture resistance parameter at 77 K MDMT. Concluding efforts applied numerical analysis to the equivalent fracture resistance equation to reaffirm the current minimum 0.53 mm (21 mils) CVN LE77K requirement for WM when MDMT is colder than 77 K and to identify minimum required [KIc/YS]277K values for cryogenic service at MDMT 77 K and warmer, and MDMT colder than 77 K. Inherently, the use of [KIc/YS]277K as a fracture resistance parameter offers a tremendous benefit to cryogenic equipment manufacturers, particularly in schedule and cost savings, as LE, KIc, and YS measured at 77 K can be used to successfully assess the fracture resistance at MDMT 77 K and warmer, as well as MDMT colder than 77 K.

Metallurgical Studies on Explosive Welded Aluminium Alloy-Stainless Steel Bimetallic Plates

Aluminium alloys and austenitic stainless steels are often used for construction of cryogenic pressure vessels owing to their attractive properties at cryogenic temperatures. Indian space programme requires AA2219/ICSS1218-SS321 bimetallic components which are machined from explosive welded plates. Pure aluminium sheet is used as an interlayer between aluminium alloy and steel to achieve a satisfactory bond. Internal soundness of the joint is evaluated through ultrasonic testing (UT). The present paper discusses bonding trials carried out by varying the explosive parameters using facilities and expertise of Terminal Ballistic Research Laboratory (TBRL), Chandigarh and M/s Giridhari Explosives Private Limited (GEPL), Hyderabad. The welded joint is extensively characterised with respect to Lap Shear and Ultimate Tensile Strength at ambient temperature and for metallographic analysis.

Cold Stretching of Cryogenic Pressure Vessels From Austenitic Stainless Steels

Austenitic stainless steel (ASS) exhibits considerable work-hardening upon deformation while retaining the characteristics of the material. The high rate of austenite deformation hardening was utilized by cold stretching (CS) of cryogenic pressure vessels. A few percent deformation will give the vessel a considerable and homogeneous yield strength improvement, and the wall thickness may be greatly reduced. The authors have conducted extensive experimental and numerical studies on CS of cryogenic pressure vessels from ASS. A summary of our work as well as a brief introduction of the history, standards, safety, and advantages of CS are given in this paper. What should be further investigated, such as fatigue properties of cold stretched ASS especially under cryogenic temperature, design of cold stretched transportable cryogenic vessels based on life, are also presented.