I agree with the comments regarding excessive heat input. After all, we would not want the base metal to exceed the melting temperature. We might get a "weld" to actually happen.
Some of the comments I read are just plain ridiculous if you take a step back and think about what is being said.
There are legitimate reasons for setting certain ground rules if they are founded on real facts, scientific principles, and take into consideration how the welded structure will be used. Unfortunately, so many "rules" are simply BS with no basis in fact.
With regards to heat input; think about how steel is made. Notice I am limiting my comments to carbon and high strength low alloys. Most every structural shape, including hollow sections, is rolled hot. How hot? Well above 1600 degrees F. Water is flooded on the surface of the steel plate and shapes to produce a protective layer of steam that prevents the formation of heavy mill scale. Can you say the "excessive heat" produced by using weave beads or multiple pass welding techniques results in any temperatures hotter than the rolling practices used every day by the steel manufacturers?
From my vantage point I have to say "yes." The temperature of the weld pool has to exceed the melting point of the steel being welding or incomplete fusion will result. However the weld pool is relatively small and still cools comparatively quickly.
Table 3.2 only has upper interpass temperature restrictions for a few select base metals, not all carbon steel and high strength low alloy steel alloys have such limitations imposed unless notch toughness is an issue. Impact properties are typically a concern when the service environment involves temperatures well below 40 degrees F. That would not affect statically loaded structures where the structural framing is enclosed in the envelop of the heated building.
The argument whether stringer beads are better than weave beads is a sucker's bet. One demonstration I often use when teaching welding is to have each welder weld a fillet break test coupon by depositing a multipass fillet weld with a 3/8 inch leg and a single pass 3/8 leg. Each welder then has to break the samples welded with a sledge hammer. In every case, and I do mean every case, the conclusion is unanimous, the single pass weave deposited in the vertical position is much harder to break. While the stringers are "stronger" because of faster cooling rates, the weave beads are more ductile and can sustain many more repeated hammer blows before failing. Try it. It might surprise you.
The goal of most welds should be to produce welded joints that are as strong as the base metals being joined. It rarely makes sense to deposit welds that are much stronger than the base metal if the resulting welds have inferior ductility. Stringer beads typically fail in the throat because they are strong, but lack ductility. The weave beads deposited with the same filler metal as the stringer beads are as strong as the base metal and typically exhibit superior ductility meaning they will undergo much more deformation before failing. The weave beads usually fail by ripping out the base metal.
There is one element that is often overlooked in any conversation, and that is welder skill. I don't care whether you use stringers or weaves, if the welder doesn't have the skill to deposit a sound weld it is going to fail any test, be it radiography or guided bend tests or a fillet break test. Skill is a function of training.
Limits placed on the width of a weave when using low hydrogen covered electrodes is not a code restriction and it is rarely imposed by the welding standard. There are no such limits imposed by NAVSEA S9074-AR-GIB-278 or NAVSEA S9074-AQ-GIB-010/248. You can go back to the NAVSEA standards and look until Hell freezes over, it isn't in there and it isn't in the D1.5 Bridge Code or D1.1 Structural Welding Code/Steel or ASME B&PV Codes (unless you are doing a repair on a PWHT'd vessel and do not plan on performing the PWHT after the repair). If you cannot cite chapter and verse and provide me with a reference clause, paragraph, or article, doesn’t waste my time with the old wives tails. Any such restrictions are imposed by the employer, not the applicable welding standard.
As mentioned, there are times when heat input is limited to control grain growth and to improve toughness when low temperature applications are involved, but that isn't the case with the majority of the structural steel that is welded. When toughness is required, the WPS has to be qualified with notch toughness testing. There are additional variables that are categorized as essential (or supplementary essential) variables imposed to account for the affects of heat input. Heat input is one control used to control the cooling rates and subsequent grain size that is important for low temperature application. The flip side of the argument is that if the application is for higher temperatures where creep is a concern, large grains "Rule," so heat input isn't limited. Heat input by itself does not destroy steel unless you are going to heat the entire structure up to the melting point, in which case you will have a molten pool of steel alloy and then who give a rat's butt whether the grain is coarse, fine, or in between.
Best regards - Al
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