Notch toughness

Low notch toughness high notch sensitivity rapid, running failures below DBT. 

Kerb-tier, n. insect, -tierkunde,/. entomology, -zahigkeit, /. (Mstal.) notch toughness, impact resistance or strength (in notched-bar test). 

The user must balance the advantages of high PWHT temperatures with other factors, such as the effect upon strength and notch toughness. Note higher PWHT temperatures can affect the ability to meet ASME Code Class 2 strength requirements. 

A 350 Carbon and Low-Alloy Steel Forgings Requiring Notch Toughness Testing for Piping... 

Requirements are placed on alloying elements in steel to control strength, weldability, and notch toughness. 

If a CRM lined pressure vessel is to be designed for below -20°F (-29°C) for reasons other than seasonal atmospheric temperature. Section VIII, Division 1 of the ASME Code requires that the materials and fabrication practices meet minimum notch toughness requirements (Paragraph UG-84). Paragraphs UCS-65, 66 and 67 cover the requirements for vessels operating below -20°F. The use of SA-36 or SA-283 is not permitted. Impact tests are required except for seasonai temperature excursions beiow -20°F (-29°C) or when exempted by paragraph UCS-66 (c) which states that "no impact test is required for materials used for metal temperatures below -20°F (-29°C) when the minimum thickness is the greater of those determined under the most severe conditions of coincident pressure (external or internal) and temperature in accordance with UG-21 for temperatures of (a) -20°F (-29°C) and above and (b) below -20°F (-29°C), in which case the coincident pressure (internal if above atmospheric pressure and external if below atmospheric pressure) shall be multiplied by 2%."... 

Steels shall have sufficient notch toughness to avoid brittle fracture under both operating and shutdown conditions. Suitable steels for atmospheric design temperatures are tabulated in API Standard 620 "Recommended Rules For Design and Construction of Large Welded, Low Pressure Storage Tanks."... 

For a comparison of the stress bases between Division 2 and other codes see Table 4-1. Allowable stresses stop at 800°F. Additional committee work is necessary before the effect of plastic deformation under creep conditions can be assessed well enough to develop adequate design rules for higher temperatures. It is believed that provisions in the area of toughness (brittle fracture) represent quite a step forward. The temperature of -20°F is no longer significant. A basic requirement is that adequate notch toughness be provided at all temperatures for all materials. 

The requirements for obtaining the desired notch toughness in weld metal are more comprehensive. Impact tests are required on the weld metal of procedure qualification test plates for all... 

Tank and pressure vessel standards have limited the 1-1/2-inch maximum thickness for welded tanks and pressure vessels, without postweld heat treatment, for many years. This limitation also recognizes the decreased notch toughness in thicker plates compared to thinner plates of the same steel specification. 

At present, the 2000(Cu), 5000(Mg), 6000(Mg-Si) series provide most of the aluminum alloys used in cryogenic applications. Established alloys in the 7000(Zn) series, including 7075, 7079, and 7178, are more sensitive to notches than many of the alloys of the above types [ 2] and have not been seriously considered. Recently, several new 7000-series alloys have been introduced with appreciably greater notch toughness than other alloys of this type. It is expected that these new alloys may be of considerable use in cryogenic applications. 

The object of this investigation was to evaluate the relative notch toughness of Al-Zn-Mg alloys X7002, X7005, X7006, X7039, and X7106 at temperatures as low as —423 F. 

The notch toughness of X7002-T6, X7006-T6, and X7039-T6 decreases with decreasing temperature, but even at —423 F, the notch yield ratios of the latter two alloys... 

The notch toughness of aluminum alloys is generally related to the level of yield strength with increase in yield strength, notch toughness, as indicated by notch yield ratio, decreases. 

A = susceptibility to hot crack formation Ah = notch toughness energy W = welds... 

Tables V and VI show that the tear strengths were generally more than twice the yield strength, further evidence of the extremely high notch toughness of these materials and their welds. For the parent metal of both alloys, the UPE values were quite high at room temperature. For alloy 5083 at 77 K, the UPE values were about 1.5 times those at room temperature. For alloy AMg6, the low-temperature values were only slightly higher than those at room temperature.

Brittle polymers, for which < 0.15 mmol/cm and Coo > 7.5. They fracture by a dominant crazing mechanism and additionally exhibit a low crack initiation energy and a low crack propagation energy (resulting in low, both uimotched and notched, toughness). Examples are PS or PMMA. 

Tito - critical temperature of brittleness in initial, unirradiated condition. This temperature is determined from Charpy V-notch impact toughness test values where criteria values of notch toughness depend on room temperature yield strength value (thus, criteria values are different for unirradiated and for irradiated conditions). For details - see Chapter 10. 

Tko is determined from values of Charpy V-notch impact test results in which only two criteria are applied notch toughness, which depends on the room temperature yield strength of a tested material, and 50% ductile appearance in fracture surfaces. Thus, there is no direct correlation between this T o and the f 7ViDT value that is used according to the AS ME for PWR vessels. Nevertheless, experimental tests give the following correlation ... 

HAZ = heat-affected zone, COD = specimens for fracture toughness testing, CHARPY, CH = specimens for impact notch toughness testing, TENSILE = specimens for static tensile testing, G-1, G-2 = designation of surveillance specimen chains). 

A 633 Normalized high-strength low-alloy structural steel Nb, V, Cr, Ni, Mo, Cu, N, Si Plate, bar, and shapes < 150 mm in thickness Enhanced notch toughness yield strength of 290 to 415 MPa in five grades Welded, bolted, or riveted structures for service at temperatures at or above -45 °C... 

A 808 High-strenglli low-aUoy steel witJi improved notch toughness V,Nb Hot-rolled plate < 65 mm in thickness Charpy V-notch impact energies of 40-60J (40-60ft Ifb) at-45 C Railway tank cars... 

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