According to the Steam Code, are inspection specimens required for such welded joints?
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The superheater coiled tubes are composed of 12Cr1MoVG in one half and 20G in the other; there is a butt joint between them. According to the standards, 12Cr1MoVG being an alloy steel requires the use of test specimens for inspection, while 20G being carbon steel does not require such test specimens. Therefore, for the welded joint between these two different types of steel, carbon steel welding wire is used as the welding material. According to the Steam Engineering Code, are inspection specimens required for welded joints of dissimilar steels?
Inspection specimens should be prepared. In accordance with the requirements of JB/T1613 \"Welding Technical Conditions for Pressure Components in Boilers\", inspection specimens are necessary even for welding between pipes made of the same material such as 20G; this is even more true when welding two different steel grades like 12Cr1MoVG and 20G.
For welding between the two dissimilar steels of 12Cr1MoVG and 20G, test specimens should be prepared. At the same time, owners should also note that: 1. When the material of the welded parts is alloy steel, metallographic testing shall be conducted on the butt welds of boiler drums under working pressures of 3.8 MPa or higher, as well as on the butt welds of headers, heat-exchange surface tubes, and pipes under working pressures of 9.8 MPa or higher or with wall temperatures of 450°C or higher. 2. For boilers with a rated steam pressure of ≥3.8 MPa, fracture inspection is performed on the butt joints of the heating surface tubes.
Of course it must be done. Sub-clause 7 of Article 93 of the Steam Boiler Code stipulates that for the butt joints of the heating surface tubes, when the material is carbon steel (except for contact welding butt joints), it is possible to waive the requirement for inspection specimens； When the material is alloy steel, under the same steel grade, welding materials, welding process, heat treatment equipment, and specifications, 0.5% of the number of joints taken from each batch of products shall be used as test specimens, provided that this number is not less than that required for one set of specimens. When it is indeed difficult to directly cut inspection specimens from the product joints, such as the butt joints where pipe joints are connected to pipes on the drum and header, as well as the butt joints of membrane wall pipes, welded simulation inspection specimens can be used. It means that it must be done as long as the joint fittings are made of alloy steel.