I had an old welder friend send me a job today to weld some cast 4130 high pressure valves. Working pressure of 15,000psi.

I have never welded 4130 and I dont even know what it is.. I will not touch the job without a WPS but even with a WPS should a guy like me that has never welded the stuff even touch it..?

My buddy just told me to pre heat it to 450 and weld it with 11018.. Im to scared to touch this stuff without more info on it..

Whats this stuf like to weld..??

You have already received some good advice on welding the 4130 steel. You have already stated that you would not weld it without a WPS, but who is to say the WPS provided by someone is valid unless you see the supporting PQR.

I have worked with 4130 on more than one occasion and in both cases the material was stress relieved after being welded.

What no one has asked is, "What welding standard is being invoked?" Perhaps the individual offering the job didn't ask or would rather you didn't know what welding code or welding standard is being invoked. There is even the possibility that they are hoping you don't ask. It sounds as if you have been around this business for a while, so you should be well aware that if this valve is being used for any purpose involving high pressure the valve is most likely required to meet the requirements of ASME. Should that be the case, you as the welding contractor, are required to qualify the WPS. You cannot use someone else's WPS. There is a probability the WPS has to be qualified with notch toughness and post weld heat treatment. Qualifying the WPS is no small undertaking in terms of cost or time. 

My advice is to know what you are getting yourself into and understand the consequences of a failure. What are the risks involved? Are you asking the customer the right questions? Do you know all the facts?

As noted in my opening, I have welded 4130. In each case I was required to qualify the WPS before welding on the product. One of the projects involved welding valve bodies that required preheats in excess of 400 degrees F and stress relief after welding. The other project also required stress relief. One project was welded with GMAW using 8018-B2L and the other project, I don't remember what we used, but it was welded with GTAW.

My suggestion is that you consider rebaking the electrodes if you are planning on welding the casting with SMAW. The 4130 is very sensitive to delayed cracking due to hydrogen. You have to consider the sum effects of the alloying constituents, not just the carbon content. You also have to consider the restrain offered by the mass of the casting. Both the carbon equivalency and the degree of restraint increases the need for high preheat temperature.

Good luck with the project.

Al