Tensile strength
The maximum force (FB) borne by the sample during tensile breaking is the stress obtained from the original cross-sectional area (so) of the sample（(σ)， Called tensile strength(σ b) , in N / mm2 (MPA). It represents the maximum ability of metal materials to resist failure under tension. The calculation formula is: Where: FB -- the maximum force borne by the sample when it is broken, n (Newton); So -- original cross-sectional area of sample, mm2.Seamless steel pipe
(1) High quality carbon structural steel grades include 20g, 20mng and 25mng. (2) Alloy structural steel grades: 15mog, 20mog, 12crmog, 15CrMoG, 12CR2MOG, 12crmovg, 12Cr3MoVSiTiB, etc. (3) In addition to ensuring chemical composition and mechanical properties, 1Cr18Ni9 and 1cr18ni11nb boiler tubes commonly used in rusty heat-resistant steel shall be subject to hydrostatic test, flaring and flattening test one by one. Steel pipes shall be delivered in heat treated condition.
Yield point
For metal materials with yield phenomenon, the stress when the specimen can continue to elongate without increasing (keeping constant) the stress during the tensile process is called the yield point. If the stress decreases, the upper and lower yield points shall be distinguished. The unit of yield point is n / mm2 (MPA). Upper yield point（σ Su): the maximum stress before the yield stress of the sample decreases for the first time; Lower yield point (σ SL): the minimum stress in the yield stage when the initial instantaneous effect is not considered. The calculation formula of yield point is: Where: FS -- yield stress (constant) of the sample during tension, n (Newton) so -- original cross-sectional area of the sample, mm2.(1) Gb3087-2008 seamless steel tubes for low and medium pressure boilers. Tensile test shall comply with GB / t228-87, hydrostatic test with GB / t241-90, flattening test with GB / t246-97, flaring test with GB / t242-97 and cold bending test with gb244-97. (2) GB5310-2008 seamless steel tubes for high pressure boilers. Tensile test, hydraulic test and flattening test are the same as those specified in gb3087-82; Impact test according to gb229-94, flaring test according to GB / t242-97 and grain size test according to Yb / t5148-93; Microstructure inspection shall be in accordance with gb13298-91, decarburized layer inspection shall be in accordance with gb224-87, and ultrasonic inspection shall be in accordance with GB / t5777-96. (3) The physical performance inspection and indexes of imported boiler tubes shall be carried out in accordance with the relevant standards specified in the contract.