Good morning wnasheim and
WELCOME TO THE AWS WELDING FORUM!!
So, First off is the four categories. They are based upon base metals according to grades considering carbon content and additional alloys as well as, if you look over one column, the welding process that will be used.
Very seldom in structural welding are you going to be in Cat A as it is welded with NON Low Hydrogen electrodes which is just plain not done in almost every circumstance. Engineers and codes are going to take you to Cat B processes for most standard shop grade materials and Cat C on occasion. Cat D is rather uncommon for most people and Cat A is just a convenience for rare occasions.
Second, according to your supplied information, both of your materials are found in Cat B if you are using Low Hydrogen electrodes (7018, 8018, etc) or the other processes considered to be of low hydrogen class in performance such as GMAW (spray arc not short arc=GMAW-S) or FCAW either shielded or not (FCAW-G = shielded and FCAW = innershield type wires).
Third, your joint configuration is not a consideration really, only the thickness of the wall on the HSS and the thickness of the plate. You will heat per the highest preheat temp which will be the thicker part when dealing with one Category and under most conditions. Remember, these are minimums. You can go over and it is usually preferable.
Fourth, while you cannot be required to preheat if your ambient temps are over 50°F, in your case for your materials, it is wise to consider doing so especially first thing in the morning to keep condensation moisture from collecting on your parts when the temperature inversion draws the H2O out of the air upon the initial striking of the arc and welding beginning. 70-100°F is a very good consideration even though not required, even later in the day when dealing with the temperatures and humidity in your area currently.
Fifth, D1.1 does not consider a maximum interpass temperature as a consideration but your preheat temp will be a minimum for every pass until the weld in the particular joint is completed.
Sixth, material preheat temps are measured 3" in all directions from the joint. On your 1" to 1/2" wall HSS you would heat the 1" plate opposite where welding will occur to insure that preheat is in the through thickness and the minimum is at preheat in the area of the weld. The 1/2" wall HSS should get enough heat by radiation, convection, etc to heat it sufficiently while heating the 1" to temperature. If you only try to heat from the welded side and barely get it to 50°, by the time they turn the torch off and set it aside and get a hood on, grab the welder, set up to weld, ...material has cooled off and is no longer preheated properly. That's why you do the opposite side but take the temp on the side where welding will occur and as the heat transfers through the rest of the steel it will maintain the minimum long enough to start the weld.
Did I make the visual acuity as transparent as earth infested H20?
Hope this helps.
He Is In Control, Have a Great Day, Brent
Topic Welding Industry / Technical Discussions / Preheat and Interpass Temperatures for OUTSIDE Welding
As Brent stated preheat for the 1" thick plate, and check the preheat at a minimum of 3" from the point of welding. To check this, the easiest way to verify your preheat is with a temperature melting crayon (tempil stick). Preheat your joint and then use the crayon to make a mark on the thicker material being welded at least 3" away, if the crayon mark melts and looks liquid and not chalky...you have reached the temperature of the crayon. Those tempil sticks are actually pretty accurate and I think they come in a variety of melting temperatures. Link to website below:
