Nil-ductility transition

Many metals that are ductile under some conditions become brittle if the conditions are altered. The effect of temperature on the nature of the fracture is of considerable importance. Many steels exhibit ductile fracture at elevated temperatures and brittle fracture at low temperatures. The temperature above which a material is ductile and below which it is brittle is known the Nil-Ductility Transition (NDT) temperature. This temperature is not precise, but varies according to prior and heat treatment and the nature and amounts of impurity elements. It is... 

The intersection of the crack arrest curve with the yield curve (Curve B) is called the fracture transition elastic (FTE) point. The temperature corresponding to this point is normally about 60°F above the NDT temperature. This temperature is also known as the Reference Temperature - Nil-ductility Transition (RTj dt) is determined in accordance with ASME Section III (1974 edition), NB 2300. The FTE is the temperature above which plastic deformation accompanies all fractures or the highest temperature at which fracture propagation can occur under purely elastic loads. The intersection of the crack arrest curve (Curve D) and the tensile strength or ultimate strength, curve (Curve A) is called the fracture transition plastic (FTP) point. The temperature corresponding with this point is normally about 120°F above the NDT temperature. Above this temperature, only ductile fractures occur. 

Nil-Ductility Transition (NDT) temperature is the temperature above which a material is ductile and below which it is brittle. 

The Nil-Ductility Transition (NDT) temperature, which is the temperature at which a given metal changes from ductile to brittle fracture, is often markedly increased by neutron irradiation. The increase in the NDT temperature is one of the most important effects of irradiation from the standpoint of nuclear power system design. For economic reasons, the large core pressure vessels of large power reactors have been constructed of low carbon steels. 

FRACTURE TEST RESULTS Nil Ductility Transition Temperature Tests... 

Standard Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels, E-208, 1975 Annual Book of ASTM Standards Part 10, ASTM, Philadelphia, Pennsylvania (1975). 

Evaluation of ferritic steels using nil-ductility transition temperature measurements correlated to fracture resistance ... 

ASTM (2006), Standard Test Method for conducting drop-weight test to determine nil-ductility transition temperature of ferritic steels, E 208-06, American Society for Testing and Materials International, West Conshohocken, PA. 

Key words fracture toughness, J-integral, master curve, irradiation, crack-arrest, embrittlement, Charpy impact, nil-ductility transition (NDT) temperature, pressurized water reactor (PWR). 

Nil-ductility transition temperature Fracture toughness Dynamic Tndt Blunt changes to sharp Sharp crack Drop-weight specimen test e.g., ASTM E 208. Uses brittle weld crack starter on test specimen. Propagation test Fracture toughness test of fatigue pre-cracked... 

Evaluation of dynamic fracture characteristics of 9Cr-lMo ferritic steel was carried out for normalised tempered (N T), aged (at 1013 K for 1-2 h) and welded conditions (with PWHT). The drop-weight nil-ductility transition temperatures (Tj ) were 248 K, 248 K and 268 K respectively for N T, aged and welded conditions. Despite the difficulties in crack-profile measurement and the uncertainties in fracture loads due to microstructural variation in HAZ of the drop-weight specimens, the particular procedure developed enabled determination of conservative estimates of at/below T. j. from instrumented drop-weight tests which are... 

Nil Ductility Transition Temperature (NDT) Also known as DBTT (ductile-brittle transition temperature) The temperature above which the material is predominantly ductile and below which it is predominantly brittle. The NDT represents the point at which the fracture energy passes below a predetermined point, i.e. 15 ft-lbs (20 joules) for ordinary steel or 40 ft-lbs (54 joules) for Cr-Mo steels. 

Some of the radionuclides produced in the materials inside the reactor pressure vessel can be used as monitors of the neutron fluence the components (e. g. the wall of the reactor pressure vessel) are exposed to during reactor operation. The materials located within the neutron field, such as the reactor pressure vessel steels, are subjected to nuclear reactions induced by fast neutrons. This can affect their mechanical properties over the course of the reactor lifetime. This applies, in particular, to the ductility of the materials as a consequence of neutron irradiation, the ductility is reduced, leading to a shift of the Nil Ductility Transition (NDT) temperature towards higher values. 

Two basic theories of failure are used in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section I, Section IV, Section 111 Division 1 (Subsections NC, ND, and NE), and Section VIII Division 1 use the maximum principal stress theory. Section ni Division 1 (Subsection NB and the optional part of NC) and Section VIII Division 2 use the maximum shear stress theory or the Tresca criterion. The maximum principal stress theory (sometimes called Rankine theory) is appropriate for materials such as cast iron at room temperature, and for mild steels at temperatures below the nil ductility transition (NDT) temperature (discussed in Section 3.7). Although this theory is used in some design codes (as mentioned previously) the reason is that of simplicity, in that it reduces the amount of analysis, although often necessitating large factors of safety. 

Reactor pressure vessel supports are subject to neutron irradiation at low temperature during plant operation. The neutron flux is lower than that at RPV, but the low irradiation temperature could result in higher embrittlement rate. Some reactor pressure vessel supports were fabricated without special requirements on fracture and radiation resistance. Steel surveillance specimens that had been irradiated in an environment believed to be similar to that in operating reactor cavities exhibited a greater than expected shift (increase) in the nil-ductility-transition temperature. This indicated that there was a potential for excessive embrittlement of reactor vessel supports. Moreover, the RPV supports are in many cases difficult to access or inaccessible for in-service inspection. 

The nil ductility transition (NDT) temperature shown in Fig. 4.11 is of significant importance when considering low strength steels. This temperature is below which the fracture appearance of steel changes from part shear to complete cleavage. Thus, this temperature is below which vessels with low strength steel must not operate without a detailed fracture evaluation. 

In 1964 a failure occurred near the nil ductility transition temperature of a large heat exchanger, under test by the Foster Wheeler Corporation. As a result of this failure and concerns raised in 1964-1965 by British researchers, the Advisory Committee on Reactor Safeguards issued a November 24, 1965 letter. While acknowledging the low probability of reactor pressure vessel failure, the Advisory Committee on Reactor Safeguards expressed concern for the... 

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