What is the difference between overall heat treatment in a furnace and ordinary overall heat treatment?
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According to Article 73, Paragraph 1 of the Regulations, high-pressure vessels, medium-pressure reaction vessels and storage vessels, horizontal storage tanks holding mixed liquefied petroleum gas, and mobile pressure vessels shall undergo overall heat treatment in a furnace. Other pressure vessels should undergo overall heat treatment. What is the difference between heat treatment in a furnace and overall heat treatment? I don’t understand this sentence. I think overall heat treatment in a furnace simply means heat treatment as a whole – can’t heat treatment be carried out outside a furnace? However, in a reply to one of the posts, outdoor heat treatment was mentioned; is outdoor heat treatment really something that exists? Please have someone who understands explain it to me. I must be ignorant. Regarding heat treatment, there is another question: for high-pressure vessels that do not meet requirement 10.4.1 of GB150 (due to insufficient plate thickness), but do meet requirement 10.4.2.1 (the ratio of the cylinder thickness to its inner diameter), is it sufficient to carry out heat treatment on the cylinder after it has been bent, or is it necessary to perform overall heat treatment in a furnace after the entire vessel has been manufactured and welded?
This issue is being discussed a lot these days. As I understand it now, overall heat treatment in a furnace means that all the equipment has to be placed inside the furnace for heat treatment； For the overall heat treatment of the remaining equipment, if the equipment is too long, one section of it can be placed inside the furnace first, while the rest is insulated outside the furnace; thereafter, that part which is outside the furnace can be put inside the furnace for heat treatment. There are also many methods for extracorporeal heat treatment: some use heating belts, while others use oil for heating. Local heat treatment of equipment makes use of more heating strips, while large spherical storage tanks are often heated using oil on-site. The last question is: It is only necessary to heat-treat the cylinder; some experts even say that after the cylinder is formed, it should be heat-treated without being welded.
Overall heat treatment in the furnace; the equipment is heated and treated inside the furnace； Overall heat treatment includes heat treatment inside the furnace, as well as heat treatment outside the furnace, such as in the case of spherical tanks, where oil is burned inside the tank while insulation is used on the outside.
There is also segmented heat treatment inside the furnace. The dimensions of the equipment exceed those specified for the heat treatment furnace; therefore, only a portion of it can be heat-treated first, with the remaining part covered to maintain insulation and prevent temperature gradients from affecting the structure and properties of the material. After that, heat-treat the other part. During segmented heat treatment, the repeated heating length should be no less than 1.5 m. Regarding the example you gave, I personally believe that although only the cylinder meets the relevant regulations, due to the special nature of heat treatment, it is still best to carry out overall heat treatment after assembling it with the head. Otherwise, you will still need to perform local heat treatment on the two circumferential seams.
The scope of overall heat treatment is broader than that of heat treatment carried out inside a furnace. For overall heat treatment, it’s sufficient to carry out heat treatment as a whole, with no restrictions on the methods used; whereas in the case of heat treatment inside a furnace, the equipment is used for heating within the furnace, and there are fixed limitations