Charpy V-notch test

API Appendix SR 8 covers Charpy V-notch testing on pipe with diameters of 16 in. (405 mm) or greater. The minimum energy acceptance level is specified by the purchaser and... 

The Charpy V-notch energy needed to arrest ductile fracture as a function of stress level for API X6G and X70 material in a 30, 36, and 42 in. (760, 915, and 1,065 mm) diameter pipe calculated from this equation is shown graphically in Figure 5.21 (A = 0.1237). The limitation of the Charpy V-notch test is that it is not a full thickness test, whereas the DWTT is. This means in thicknesses more than in., compensation in the form of increased energy absorption requirements is often specified for thick pipe. 

The design temperature should be at least 10°F (6°C) higher than the testing temperatures shown in the table, since it will be necessary to meet Charpy V notch test requirements in the heat affected zones of welds. Also the minimum temperatures listed are for longitudinal tests. For transverse tests, the minimum testing temperature may be higher. It should also be noted that plates must be normalized or quenched and tempered to meet these requirements. 

Table 4.5 gives an example of the content of capsules of 900 MWe reactors. Charpy V-notch tests are used to monitor all the materials. Additional tensile and fracture toughness tests are carried out for base and weld metals. Most reactors have four surveillance capsules to cover their design lifetime (40 years), except the first series of six 900MWe reactors known as CPO which have eight capsules. Generally, capsules are planned to be removed so that irradiation at quarter, half, three-quarters and completion of the component design end-of-life fluence can be achieved (Brillaud and Hedin, 1992 Chas et al, 2004). Table 4.6 shows the lead factors, defined by... 

In accordance with 10 CFR 50 Appendix G, Paragraph IV A, the reactor vessel beltline materials have minimum upper-shelf energy, as determined from Charpy V-notch tests on unirradiated specimens in accordance with Paragraphs NB-2322.2(a) of the ASME Code, of 75 ft-lbs. Charpy impact tests will be performed on... 

Charpy impact testing, also known as Charpy V notch testing, is performed on materials to determine toughness properties, usuaUy at low temperature. CIT enables one to determine the transition temperature between brittle and ductile faUure for any material or material specimen. CIT is also a good indication of a materials abiUty to absorb shock loads at low temperatures. CIT is used predominantly for carbon and low aUoy steels. It is not used for stainless steels because stainless steels do not fail in a brittle manner until extremely low temperatmes. 

Table 2.3 Charpy V-Notch Test Performance Requirements - Anchor Material...

Materials selection for low-temperature service is a specialized area. In general, it is necessaiy to select materials and fabrication methods which will provide adequate toughness at all operating conditions. It is frequently necessaiy to specify Charpy V-notch (or other appropriate) qu fication tests to demonstrate adequate toughness of carbon and low-aUoy steels at minimum operating temperatures. 

All pressure retaining steels applied at a specified minimum design metal temperature (2.11.4.5) below -30°C (-20°F) require a Charpy V-notch impact test of the base metal and the weld joint unless they are exempt in accordance with the requirements of paragraph UHA-51 in Section Vlll, Division 1 of the ASME Code. Impact test results shall meet the requirements of paragraph UG-84 of the Code. 

How finishing temperature affects the Figure 5.13 Long distance rupturing of pipe tested Charpy V-notch 50% shear fracture- wjth aagii... 

Note 4 Each plate shall be impact tested and meet the Charpy V notch (ASTM A 370, Type) requirements of Par. 2.2.3 of API Specification 620. 

The grades of steel normally specified for low temperature service and the minimum temperature of mill Charpy V notch acceptance testing, as abstracted from ASTM A-20-81b "Standard Specification For General Requirements For Steel Plates For Pressure Vessels" are as shown in Table 3-2. 

Table 3-2 Generally Available Grade-Thickness-Minimum Test Temperature Combinations Meeting Charpy V-Notch Requirements Indicated...

The cost of using other steels was calculated in a similar manner, using additional quality, pressure vessel, fine grain practice, heat treatment and Charpy V notch impact test extras appropriate for each grade. An additional extra of 0.30 per cwt was included for the non standard thicknesses calculated for steels other than SA-36. 

Some specifications require a minimum Charpy v notch impact requirement of 15 ft lb energy absorbed at the minimum expected service temperature. However, this does not mean that a test specimen exhibiting 60 ft lb is four times tougher than the minimum. The main value of notched bar impact testing is as a criterion for acceptance of materials where reliable correlation with service behavior has been obtained. 

Scientists (Ref 12) welded HSLA-65 using tungsten-base tools. Subjected to bend tests, a 10 mm (0.4 in.) thick weld passed, and a 6 mm (0.24 in.) thick weld failed when bent with the root in tension, due to the formation of surface cracks. Tensile properties of the 10 mm thick welds exceeded the specifications for the base metal. Some 6 mm thick welds exceeded the plate specifications, while others were approximately 10% below the plate specifications. Charpy V-notch (CVN) toughness at both -29 and 0 °C (-20 and 0 °F) were below the base material toughness but exceeded the minimum specification of the plate. The surface of the welded material was found to have small defects due to the roughness caused by the interaction between the shoulder and the surface of the plate. Salt spray corrosion tests indicated no preference for corrosion in the weld zone. 

The report of the inquiry [111] criticised the design and fabrication of the alterations made to the original pontoon. The actual cause of the accident was the failure of some tie bars in the detail around the jacking points. The failure was due to brittle fracture which initiated from severe notches such as a small radius curve at the fillet between the spade end and the shank of the tie bar. Weld defects and fatigue cracks were also present in tie bars subsequently recovered from the sea bed. The tie bars had been flame cut to shape and had weld repairs visible to the eye. There had been no post welding heat treatment of the steel. The steel complied with the original specification but tests showed low Charpy V notch impact values. Photo elastic tests indicated a stress concentration factor of 7 at the fillet between the spade end and the shank. The fracture was initiated in the opinion of the inquiry tribunal by the low ambient temperature of around 3°C. 

Within FP-5 project FRAME work will be done to improve the assessment of the most important parameter used to measure the embrittlement conditions of the RPV. Currently this is done through indirect measurements in a rather conservative way (the so-called reference temperature methodology, which makes use of Charpy-V notch impact testing). It is difficult to estimate in a quantitative way the conservatism of this methodology. Therefore the work proposed will focus on the development of a method which allows to measure directly the fracture toughness. This should result in a better and more accurate estimation of the embrittlement conditions of the RPV material. 

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