Comparative analysis of SA210A-1, SA210C and 20G carbon steel for high pressure boilers
The research found that the current domestic production of SA210A-1 does not have a separate billet in the actual material supply, and it is usually substituted by SA210C billet or 20G billet. In order to study whether this substitution can meet the SA210A-1 material standards and product design requirements, through a comparative analysis of the composition and properties of SA210A-1, SA210C and 20G in the SA210M standard and GB 5310 standard, the optimization opinion that the lower limit of Mn should be added to the SA210A-1 small diameter pipe procurement requirements is proposed.
0 Preface
The current parameter level in the sub-critical and above boiler unit pressure-bearing parts with carbon steel materials are mainly three types: 20G, SA210A-1, SA210C, basically used for low-temperature superheater, low-temperature reheater, water-cooled wall and coal saver and other components in the heated surface tube, tube metal design temperature is usually 350 ℃ ~ 425 ℃ .
Since the strengthening elements of carbon steel are C and Mn, and boiler manufacturers usually strictly limit the C content from welding performance considerations. According to the description in ASME: for every 0.01% decrease in carbon content below the specified maximum carbon content, it is allowed to increase the manganese content by 0.06% each above the specified maximum manganese content, but the maximum shall not exceed 1.35%. Description of the loss of strength brought about by a decrease in carbon content generally requires 6 manganese content to compensate, but the actual supply of materials from the current steel pipe mill found an interesting phenomenon: that is, the domestic SA210A-1 seems to have no distinctive composition of the individual billet, either SA210C billet instead, or 20G billet instead, this phenomenon can be randomly selected in Table 1 part of the batch SA210A-1, SA210C, 20G SA210C, 20G, the composition and performance data comparison to get a visual impression, the difference is more obviously reflected in the Mn content. Also for SA210A-1, the composition and properties of serial numbers 6, 7 and 8 in Table 1 are comparable to those of 20G, and the composition and properties of serial number 9 are comparable to those of SA210C. So can this substitution ensure that SA210A-1 meets the material standards and product design requirements? The following analysis follows the lineage of the standard and is combined with the conditions of use of the product.
1 Comparison and analysis
1.1 Comparative analysis of SA210A-1 and SA210C
The main difference between SA210A-1 and 210C lies in the C content (Table 2), which is reflected in the performance of SA210C, whose strength is about 10% higher than that of SA210A-1 (Table 3), and whose design allowable stress is 10% higher than that of SA210A-1 in the design temperature range from 350℃ to 425℃ (Table 4), which indicates that Under the same working conditions, the wall thickness of SA210C pipe can be reduced by about 10% compared to SA210A-1, so SA210A-1 with SA210C billet means that the wall thickness margin can be increased by 10%.
Table 1 reflects that although the actual carbon content of the supplied SA210C is not high, the increased Mn content makes up for the reduced strength of C.
1.2 Comparative analysis of SA210A-1 and 20G
20G is the steel number in GB 5310-2008, from the composition list alone (Table 5), 20G and SA210A-1 composition has a compatible area, it seems that the two can replace each other, but from the high temperature yield and allowable stress (Table 6), SA210A-1 high temperature yield is more than 10% higher than 20G, SA210A-1 in the 350 ℃ ~ 425 ℃ zone design allowable stress About 10% higher than the average 20G, which indicates that SA210A-1 selection of 20G billet, from the performance of low instead of high, if the original SA210A-1 wall thickness margin is not sufficient, is implied a certain risk.
2 Print
GB 5310 since the 1995 edition with reference to foreign common standards, increased the corresponding steel grades, such as SA210A-1 increased steel grade is 20MnG, as opposed to SA210C increased steel grade is 25MnG. As a typical production-oriented standards, GB5310 combined with the use of domestic boiler steel characteristics, the original ASME grades of broad requirements for refinement and qualification, mainly in the provisions of C and M. The main manifestation is the stipulation of C and Mn composition interval, especially the lower limit of Mn is raised to 0.7%, which is higher than the upper limit of Mn in 20G. Table 8, 9, 10 are the national standard series of three steel composition, performance and allowable stress comparison.
Table 10 clearly reflects that the design allowable stress of 20MnG equivalent to SA210A-1 is about 10% higher than that of 20G in the range of 350℃~425℃, and the design allowable stress of 25MnG equivalent to SA210C is about 20% higher than that of 20G and about 10% higher than that of 20MnG, which is consistent with the aforementioned results.
3 Conclusion
(1) As the material usually used for boiler pressure parts with metal design temperature between 350℃ and 425℃, the design allowable stress of SA210A-1 is about 10% lower than that of SA210C and about 10% higher than that of 20G.
(2) Considering the use characteristics of boiler steel, in order to ensure that SA210A-1 meet the material standards and product design requirements, SA210A-1 composition design should be optimized, in SA210A-1 small diameter tube procurement technical conditions, increase the Mn content of 0.7 lower limit provisions.
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