Weld specimens, tests

In view of the widespread use of welded joints in equipment and structures exposed to corrosion, it is necessary to know whether such welded joints will demonstrate satisfactory resistance to attack. It is not necessary to include welded specimens of all materials in a preliminary study to discover which of them have satisfactory resistance to a particular environment. Weld tests can be postponed until the preliminary selection has been made, or, alternatively, those materials expected in advance to be most likely to be resistant can be exposed in the welded condition so as to expedite the final answer. 

Table 8. Conditions of low-cycle fatigue tests of welded specimens...

On the other hand, it can also be concluded that the defect-free weld of alloy T110 is a less effective stress raiser than the radius transition in a specimen tested. 

Fractographic examinations were performed on fracture surfaces of both tensile and the unidirectional fatigue specimens tested at various temperatures. An extensive discussion and numerous fractographs of both the base metal and welded... 

The specimens were cut from the plate in two directions longitudinal and transverse to the rolling direction. The welded joint specimens were cut transverse to the weld. The notch in the welded joint specimens was made in the plane parallel to the weld direction. Tests were conducted at room temperature and at 77 K. The topographical features of the fracture surfaces of notched specimens were revealed by the fractographic method and with a scanning electron microscope (SEM). 

Because of the high toughness of the base metal and welded joints and the small sizes of the specimens tested, the actual values for Kjc (the coefficient of stress intensity under conditions of plane deformation) could not be obtained. To compare the variables of the specimens studied, a coefficient of stress intensity under maximum load, Kj x, was taken as a characteristic of fracture toughness. In this case, the testing method and shapes and sizes of the specimens were about the same as those used by Kelsey and Nelson [%... 

In the weldment tests, both gas metal and shielded metal arc welds were tested. Except for the OX13AG19 weldment, the weld joint preparation was in the form of a K, to ensure straight HAZs. These specimens were notched and fatigue... 

For calculation of 50 % (median) curves of AT i(F, t) according to Eq. 5.5, the value a = 0 should be taken, both for base and weld metal. This type of dependence is used for direct determination of radiation embrittlement parameters based on results of RPV-specilic surveillance specimen tests. Typical trend curves calculated according to the Eq. 5.4 for base metal and weld metal are shown in Figs 5.2 and 5.3. It can be seen that mean curves provide a good description of the distribution of test results from surveillance specimen programmes. 

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... 

Concerning the specimens tested in Turkey, those of Teymur et al. (2008), AnU and Altin (2007) were single storey one-bay 1 2 and 1 3 scale, with RC infill thickness 25 and 33 % of the width of the frame members. Those of Altin et al. (1992), Turk et al. (2003), Canbay et al. (2003), Sonuvar et al. (2004), Kara and Altin (2006) were two-storey one-bay scaled at 1 3, with infill wall thickness 33 and 40 % of the width of the members of the bounding frame. The RC infill was in most cases fully connected on the perimeter with dowels in some cases (Teymur et al. 2008) there was a gap between the infill and the columns in some other cases there was no connection other than simple bearing. Altin et al. (1992) proposed to weld... 

The appearance of the fatigue fractures in specimens tested at both 75 and -300 F are quite typical of those stressed in reversed bending (Fig. 16). All fractures disclosed the characteristic mother-of-pearl" or "oyster shell" appearance. The nucleus of the fracture almost invariably is at die surface. The bead-on specimens fractured invariably at the plate, weld bead interface at both test temperatures. This is expected, since there is a geometrical or mechanical notch created by the bead. TTie bead-off specimens fractured either in the weld deposit or heat-affected zone when tested at 75 F. The location of the fracture appears unrelated to stress level and may merely represent the statistical chance of failing in either one of those two locations. At -300 F, the bead-off specimens fractured in the weld, indicating that the metallurgical notch, created by the weld deposit and heat-affected zone, has become relatively unimportant at this low temperature. 

While many laboratory tests for resistance of metals to stress corrosion cracking have been developed, only a few tests are amenable to actual in-situ testing in seawater. These primarily consist of the exposure of statically stressed type test specimens such as described in ASTM G 30, G 38, G 39, and ISO 7539-2, ISO 7539-3, and ISO 7539-5. In addition, welded specimens such as described in ASTM G 58 are excellent for evaluation of the stress corrosion resistance of weldments in simple immersion tests. Evaluation of corrosion fatigue is usually limited to laboratory testing. 

ASTM G 58, Practice for Preparation of Stress Corrosion Test Specimens for Weldments— This covers the manufacture and application of welded test specimens in stress corrosion testing. This practice is used to evaluate a total weldment, weld metal, or presence of notches and stress risers in weldments with respect to SCC in an environment. In addition, ASTM G 58 contains a method for evaluating the critical stress levels that will produce SCC in a weldment. The specimens are evaluated after exposure to an environment by microscopic methods. This standard includes typical specimens (stressed and tension), welding considerations, test specimen preparation, and inspection after exposure. 

Heat and/or mechanical deformation may lead to loss of corrosion resistance. Welding may cause severe problems for certain materials for example, sensitization of the base metal in the heat-affected-zone, or molybdenum segregation of weld metal. Welded specimens are often tested to study potential problems. Specimens may be deformed to study the effect of residual stresses fi-om forming or welding. U-bend specimens are often exposed. If sp>ace is restricted, a Brinell hardness indentation can be used on a flat specimen to create a region of high residual stress. 

The drop in the impact strength between 196 K and 24°K of the weld metal was accompanied by a change in the mode of fracture. A small area of cleavage developed at the 196 to 78 K range and increased to an area approximately 1/3 of the fracture surface at 24 K, However, there was still some plastic deformation at 24 K, All the welded specimens separated into two pieces. Figures 18 and 19 of the welded impact specimens tested at 300 and 20°K, respectively, show that fracture occurred within the grains at both temperatures, The fracture of the parent specimen appeared to be pure shear down to 24 K. The specimens did not break... 

Specimens were machine welded by the inert gas shielded tungsten arc process using 4043 aluminum alloy filler wire. Welded specimen blanks such as shown in Figure 4a were furnished by the Martin Company and machined as shown in Figure 4b, It was necessary, however, in the fatigue testing to reduce the specimen width and the pin and hole diameter to avoid failures through the pin hole. 

In Phase I specimens tested at subzero temperatures were held at temperature a minimum of 10 hours, before testing. Those tested above room temperature were heated from room temperature to test temperatures in 30 seconds and held three minutes before load was applied. The stress was calculated on the cross sectional area of the sheet although at temperatures below 200 F failure was always in the weld. Figure 5 shows the results of Phase I. The different results obtained on the three thicknesses probably reflect differences in the effect of the uniform welding procedure on materials of different thickness, although some difference in strength of the base metal may be expected. 

---