CEMP-E
TI 809-26
1 March 2000
quenched and tempered steels, too high a preheat may affect steel properties by retempering the steel.
For quenched and tempered steels, preheat and interpass temperatures above 230oC (450oF) should be
avoided.
b. Preheat for Prequalified Applications. The basic values for minimum preheat temperatures for
prequalified structural steels are provided in AWS D1.1 Table 3.2. A summary of this table is provided as
Table 3-1, with suggestions in Table 3-2 for non-prequalified steels. With any non-prequalified steel, a
competent welding advisor should be consulted. When steels of different categories are joined, use the
higher preheat required for their respective thicknesses.
(1) Category A is applicable when non-low hydrogen SMAW electrodes are used. This is permitted
as prequalified only for AWS Group I steels, but is not recommended practice. See Appendix C,
Paragraph 1b. Because of the higher diffusible hydrogen present when non-low hydrogen electrodes are
used, higher preheats are required to allow additional time for hydrogen to escape from the heat-affected
zone. When low-hydrogen SMAW electrodes are used, the preheat can be reduced because of the
reduced hydrogen levels present.
(2) Category D is applicable to A913 steel, a thermo-mechanically controlled processed (TMCP)
steel that has low carbon and alloy levels. Weldability tests have been conducted to document that the
steel may be welded without preheat, provided the steel temperature is above 0oC (32oF), and an
electrode classified as H8 (tested under ANSI/AWS A4.3 for 8 mL or less of diffusible hydrogen per 100
g of deposited weld metal) or lower is used.
(3) Users are cautioned that the use of these minimum preheat tables may not be sufficient to
avoid cracking in all cases. Increased preheat temperatures may be necessary in situations involving
higher restraint, higher hydrogen levels, lower welding heat input, or with steel compositions at the upper
end of their respective specification. Conversely, preheats lower than those tabulated may be adequate
for conditions of low restraint, low hydrogen levels, higher welding heat input, and steel compositions low
in carbon and other alloys. Additional guidance for these situations may be found in AWS D1.1 Annex XI,
Guideline on Alternative Methods for Determining Preheat. The Guide considers hydrogen level, steel
composition, and restraint and allows for calculation of the estimated preheat necessary to avoid cold
cracking. When higher preheats are calculated, it is advisable to use these values, provided maximum
preheat levels are not exceeded. When lower preheat values are calculated, the AWS D1.1 Code
requires the WPS to be qualified using the lower preheat value. Such testing may not always adequately
replicate restraint conditions, so caution is advised.
(4) Although not required for building applications under AWS D1.1, consideration for higher
preheat and interpass temperature requirements may be made for critical applications where fracture
would result in a catastrophic collapse. For these conditions, AWS D1.5 Bridge Welding Code Tables
12.3, 12.4 and 12.5 provide recommended values. Seismic applications with routine building structures is
not considered appropriate for requiring higher levels of preheat and interpass temperatures, and AWS
D1.1 Table 3.2 should suffice.
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