Preheat and interpass temperature

It has been assumed that local preheat is used, that it is applied along the weld line, and that the temperature on both sides of the joint is measured at least 75 mm from the weld line on the opposite side of the plate to that being heated. If the temperature can be 

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Preheat and interpass temperature shall be as specified/qualified per the applicable WPS/PQR. ... 

The permissible maximum carbon equivalent for butt welds in line pipe using cellulosic (EXX10) electrodes based on minimum preheat and interpass temperature, pipe wall... 

Preheat is not required for grades up to API X52 when the CE is less than 0.5 to 0.55 [by Equation (5.1)]. Equation (5.2) is commonly used in specifications. Limiting the Equation (2) CE to 0.42 for X60 through X70 grades is usually required. The maximum CE, based on preheat and interpass temperature, wall thickness, and heat input (travel speed), can be estimated from Figure 5.10. For example, for 0.42 CE and 1 in. (25 mm) wail pipe, a preheat of 68° F (20° C) would be required for a 12 KJ/cm heat input however, if the heat input was reduced to 9 KJ/cm, then a 140 F (60° C) preheat would be required. 

It may also be necessary to decide limitations on the level of preheat and interpass temperature which can be used for example, welding manually within an enclosed space may preclude high temperatures. 

At low hardness values (below about 450 HV), low preheat and interpass temperatures are predicted and postweld heating may not be necessary. A further reduction of temperature may be possible if very low hydrogen processes can be used, but this should be confirmed by joint simulation tests. For example, in maraging steels graded M and having a maximum carbon content of 0.02%, Fig. 

PWHT or radiography depends upon carbon content, grade of material, type of welding, thickness, preheat and Interpass temperatures, and types of electrodes. See ASME Code, Section VIII, Div. 1 Table UHA-32, and paragraphs UHA 32 and 33 for concessions/restriclions. 

PWHT or radiography depends upon carbon content, grade of material, type of welding, thickness, preheat and interpass temperatures, and types of electrodes. See ASME Code, Section VIII, Div. 1 Table UHA-32, and paragraphs UHA 32 and 33 for concessions/restrictions. Radiography shall be performed after PWHT when required. 100% R.T. is required for all vessels in lethal service (ASME Code UW-2(a)). Materials requiring impact testing for low temperature service shall be PWHT (ASME Code, UCS-67 c)). 

For hardenable steels the carbon content is used to select preheat, interpass and postheat temperatures. 

Diagram for selecting minimum preheat, interpass and postheat temperatures for alloy and lean alloy steels giving fully hardened HAZs. Note relaxation of preheat temperatures may be possible with low hydrogen processes and thin sections, particularly at low C contents. Confirmation should be obtained by joint simulation tests. For class of steel refer to Table 4.3... 

Diagram for selecting minimum preheat, interpass, and postheat temperatures (carbon and C-Mn steels with fully hardened HAZs). 

For values of this parameter, F, up to 115, a steel is graded carbon steels . For values from 116-145 the steel is graded carbon-manganese steels and examples can be found in Table 4.3. For these two grades the relationship between carbon content and expected HAZ hardness is given in Fig. 4.7, and its subsequent use to establish minimum preheat, interpass, and postheat temperatures is exactly as described previously. 

Paragraph C.l.b implies that the qualification materials are an infinite heat sink that would instantaneously dissipate the heat input from the welding process. The qualification procedure consists of starting the welding at the minimum preheat temperature. Welding is continued until the maximum interpass temperature is reached. At this time, the test material is permitted to cool to the minimum preheat temperature and the welding is restarted. Preheat temperatures utilized for low alloy steel are in accordance with Section III of the ASME Code. The maximum interpass temperature utilized is 500°F. 

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