Level weld metal

As the weld metal solidifies, impurity elements are rejected into the molten weld pool, eg, sulfur and phosphoms in steel welds (Fig. 7) (8). The final weld metal to soHdify, located along the weld centerline at the surface of the weld, has increased levels of these elements, which act to lower the... 

These recent tests were conducted at applied stress levels similar to those that might be experienced by ASME Section Vm, Division 2 vessels. Test exposure times exceeded 50,000 hours depending on applied stress and temperature. The test specimens were from weldments of thick section plates and represented base metal, weld metal, and heat-affected zone. Detrimental effects of hydrogen were found down to the Figure 1 limit of 850°F (454°C) at 2000 pounds per square inch absolute (14 megapascals) and 3000 pounds per square inch absolute (21 megapascals) hydrogen partial pressure. 

It is very difficult and not practical to decrease the depths of the flights by welding metal back into the channels. This level of welding is generally unacceptable due to the large level of bends that will occur in the screw. For this case, it is often less costly and quicker to build a new screw with shallower channels. 

Step 3 Decide combined thickness of joint in question (Chapter 3). Step 4 Decide limitations on heat input, bead size, or electrode size which can he used (Chapter 3). These limitations may arise because of positional welding or because of a need to achieve minimum toughness levels in weld metal or HAZ. Step 5 Trace horizontal line to obtain required preheat level. 

As yet there are few comprehensive data to determine the preheat levels necessary to avoid weld metal hydrogen cracking. 

Increasing parent metal hardenability or weld metal hydrogen level. ... 

A3 General relationships between potential hydrogen and weld metal hydrogen levels. 

Normally, a minimum preheat temperature is required when it is necessary to achieve particular levels of toughness and/or strength in the HAZ or weld metal a maximum value may also be required. Preheat may be local or general. It is recommended that the former should be measured at least 75 mm from the weld line. 

Welded microstructures can be extremely complex and often ehange drastically over a very short distance. The fusion zone or weld metal is a dendritic structure that solidified from a molten state. Bordering the fusion zone are transition, unmixed and partially melted zones, and the HAZ. These zones ean be reheated and altered by subsequent weld passes in multipass welding. For alloys with structures dependent on thermal history such as steels, the final microstructure ean be very complex. As welded stmctures are often quite susceptible to corrosion, overalloyed filler metals are often used to increase the weld corrosion resistance. In the case of stainless steels with high levels of carbon content, sensitization in the HAZ is another problem (4). 

By the method of mathematical multifactor planning of the experiment, equations were derived that describe the dependence of the mechanical properties of parent and weld metals on the chemical composition of the alloy. Table III shows the investigated factors, intervals, and levels of variation. Characteristics of mechanical properties and the index of alloy susceptibility to hot cracking of weld metal during welding served as functions of response. 

At 923 K, the stress exponent for minimum creep rate is about 9.5 for both the base metals, whereas it is about 12 for the weld metals. However, in the case of SS 316, the weld metal exhibited higher creep rates compared to the base metal whereas forSS316LN the creep rate of the weld metal was lower by a factor of 5 at high stress levels and 10 at lower stress levels, compared to that of its base metal. Both the weld metal exhibited lower rupture elongation compared to that of the respective base metals at 873 and 923 K. Comparison of the rupture lives of the two steels with the ASME Code Case N-47 curves for the base and weld metals showed that in the case of SS 316 LN, the codal allowable stresses are over-conservative. 

The neutron flux level for the PWR surveillance program is approximately 10 n/cm s ( > 1 MeV). The highest fluence of the PWR surveillance data is about 6 x 10 n/cm (E > IMeV) as of 2012. The transition temperature shifts, ARTndtS, of all the PWR surveillance data are plotted in Fig. 4.12 for base metals and Fig. 4.13 for weld metals as a function of neutron fluence. In general, ARTndt increases with fluence, but the values of the shift are not very high. The highest ARTndt values for base metal and weld metal are 88 °C and 131 C, respectively. The transition temperature shift depends mainly on the copper content of steel, and it increases with the copper content. 

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