Steven, I hope you don't think anyone is talking down to you, I just don't see it in the thread. They are obviously asking about technical details that push the boundaries of your technical experience, but they are absolutely correct - if the chemical composition of the pipe is unknown, its pretty nearly impossible to say what preheat might be required. The mission of the AWS is to advance the science of welding and these forums generally reflect that. I have seen a few rude answers and uncalled for personal comments in the past, but they are not very common. On the contrary, I think about 99% of the posting in the various forums is people trying to help one another to the best of their individual abilities, and you will find that a lot of the people here have a great deal of expertise in various areas of welding.
Now if you are talking about API 5L-X80 SMLS the only chemistry requirement is P 0.045 ~ 0.085 believe it or not (Surprised me), for welded pipe (the one with the subarc seam down the length, the chemical requirements are 0.18 C max, 0.030 P max, 0.018 S max. No chrome is specified.
For this type of pipe, at 70 degrees ambient, in the thickness you indicated, no preheat should be required. I know we have some pipeliners in the audience, so feel free to correct if necessary. 600 degrees seems detrimental to me to notch toughness, so if some one was asking me, I would recommend against it.
There are other specifications of pipe, P5, P11, P15, etc. that do have a chrome content. They require both preheat in the range of 300-400 degrees and frequently a post weld stress relief. See if you can find out what the specification and grade of the pipe you are welding is - very often its marked right on the pipe. If not the welding foreman should know.
Finally, and I hope you see this is as advice rather than talking down to you, it's fine for a welder to question a procedure, that shows his brain is engaged, but its not good for a welder to blow off some portion of a procedure because its just all wrong or inconvenient in his opinion. Remember that the procedure was qualified taking into account a lot of variables we haven't even touched on here. Acceptable mechanical results were obtained with the procedure parameters. If the welder changes those parameters will the results still be acceptable? Nobody truly knows without running another procedure qualification incorporating the welder's parameters. And all that doesn't even address that the customer has to approve procedures (usually), which is sometimes a very involved process, absorbing a lot of time and money.
Bear in mind that being young and inexperienced in the technical issues of welding is not a negative. It's an opportunity. There are lots of sources of materials to widen your knowledge if you desire, to the point that you're the guy writing the procedures (and getting it right), or the guy writing the inspection procedures.
Steven,
Back up, breathe in, breathe out, relax, don't get your back up. We are trying to be helpful. 3.2 may have been a little sharp with his comment, but I feel it is more than a little accurate. I for one am not "bent out of shape" and do not believe 3.2 is either.
Are you really wanting to learn, or looking for fast, simple answers on the back of the experience and knowledge of others? True learners don't get easily offended even when the truth hurts.
We do not think you are an "idiot" and I did not feel we were talking "down" to you. I am a certified welder before all else. Have been for over 35 years. I am a business owner second. Have been twice, this time for 12 years in the same shop. I am next a CWI. Short time and still learning lots. We all need to be continually learning to improve ourselves as well as our profession. And yes, I do take my profession as well as my job very seriously.
Now, as to your question, which we are trying to deal with. There are many codes for welding. We do need to know which one you are dealing with in order to give you the best information. It does show a lack of knowledge when you don't know which code you are being expected to work to. Do you even know if you are certified to the proper code for the job? This would be lesson one. Find out if you don't know.
Lesson two: Do you know what an MTR (Material Test Report) is? Important information for both code application and WPS application (Welding Procedure Specification). The MTR would tell you all the chemical breakdown of the material being used. Get a copy of it if possible, at least a look at it.
Lesson three: all steels can require pre-heat at some point. Depends upon grade, thickness, ambient temperatures, welding process to be used, filler specs, and code to be welded to. That is why all the previous info is needed. Then the correct charts can be used to find the correct pre-heat, interpass, and post heat temperatures to be used.
Most here are willing and able to be of great assistance. At the same time we like to see people asking questions in a way that indicates they are willing to learn and are trying to do the job themselves.
So, let's try again, begin with the breathing, relax, learn, apply. Code worked to, steel used. Find out these things and we may be able to help you learn to help yourself. Will make you more valuable to yourself, your employer, and others down the road.
Have a Great Day, Brent
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