There are three ways to combat sensitization: the first is to use a low carbon base and filler metal to reduce or eliminate carbon. This in turn allows the steel to corrode or it will not have the intended corrosion resistance. If you raise the carbon levels in the weld and neighboring heat affected zone, it forms chromium carbides, which tie up the chromium, preventing the formation of chromium oxide. ![]() Chromium oxide is the “stainless” layer of stainless steel. Sensitization is the primary cause of the loss of corrosion resistance and is affected by the chemistry of the base material and filler metal, as well as the temperatures at which the weld cools. Controlling sensitization with filler metals, interpass temperature control They include tin, antimony, arsenic, phosphorus and sulfur, and can have strong effects on corrosion resistance. These are residual elements in the raw materials used to make filler metals. When welding stainless steels, it’s also important to select a filler metal with low trace (or “tramp”) elements. The 309 series filler metals are also particularly adept at joining dissimilar stainless steels and in overlay applications. Filler metals with higher silicon levels, such as ER309LSi, increase weld puddle fluidity, improve tie-ins and increase travel speeds for greater productivity. Conversely, a filler metal with an “H” designation provides higher carbon content for applications requiring greater strength, particularly at high temperatures. In high purity applications – food, beverage, pharmaceutical – that low carbon content is critical for maintaining corrosion resistance. For example: if you weld a 304L base metal with a standard 308 filler metal, you’ll actually raise the carbon content of that joint and increase the chance of corrosion. This can help retain corrosion resistance in low carbon stainless alloys. Filler metals with an “L” designation, such as ER308L, provide a lower maximum carbon content. Selecting filler metal for stainless steel pipe is about enhancing the properties of the weld and meeting the application's requirements. Filler metal selection critical in controlling carbon levels ![]() It is meant to spur ideas as to how to move your own welding practices forward. Each process detailed in this article has been certified in critical applications. Within those basics, we will present best practices and new wrinkles on established methods that may help drive productivity in your shop while improving or maintaining the desired corrosion resistance.Īs a note: critical applications where processes are certified should not be altered without going through appropriate certification processes. This article will cover the basics of welding stainless steel tube and pipe for applications ranging from high purity food and beverage, pharmaceutical and petrochemical pipe to oil and gas applications. However, evolutions to well-established processes and techniques allow pipe fabricators to increase productivity without sacrificing the corrosion resistance of the stainless steel. Proper selection of filler metals, joint preparation, cleanliness and welding processes help ensure the final product meets the designated quality standards and retains its intended corrosion resistant qualities. There’s no voodoo when it comes to welding stainless steel tube and pipe. (Reader's Note: As originally seen in The Welding Journal (American Welding Society)).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |