Allowable stresses of bolt materials      

    

Material	Diameter of bolt, d (mm)	Heat treatment	Allowable stress (MPa) The smallest in the listed below
Carbon steel	d≤M22 M24≤d≤M48	Hot rolling, normalization	σ ts/2.7 σ ts/2.5	σ tD/1.5
Low alloy steel, martensite high-alloy steel	d≤M22 M24≤d≤M48 d≥M52	Tempering	σ ts(σt0.2)/3.5 σ ts(σt0.2)/3.0 σ ts(σt0.2)/2.7	σ tD/1.5
Austenic high-alloy steel	d≤M22 M24≤d≤M48	Solution	σ ts(σt0.2)/1.6 σ ts(σt0.2)/1.5

 

Material	Allowable stress (MPa) The smallest in the listed below
Carbon steel and low alloy steel		sb			ss				σ ts			σ tD		σ tn
		3.0			1.6				1.6			1.5		1.0
High-alloy steel		sb		ss(s0.2)				σ ts(σt0.2)				σ tD		σ tn
		3.0		1.5				1.5				1.5		1.5
Non-ferrous metal		sb		ss(s0.2)				σ ts(σt0.2)				—		—
		4.0		1.5				1.5

 

Note: For Austenic high-alloy steel piping components, the allowable stress may be reasonably heightened to 0.9 times ofσ ts(σ^t_0.2), but should not exceed 0.667 times ofσ_s (σ_0.2) when the design temperature is lower than the creep temperature rang, and tiny residual deformation is allowed. However, this stipulation is not applicable for flanges or other situations where even a tiny residual deformation will cause leakage or failure.

Symbols in this table mean:

 

σb σS (σ0.2)   σ ts (σt0.2)   σ tD   σ tn

— —   —   —   —

The lower limit value of the standard tensile strength of a material (MPa); The normal yield point of a material at the normal temperature (0.2% of the yield strength) (MPa); The normal yield point of a material at the design temperature (0.2% of the yield strength) (MPa); The aveage value of the creep rupture strengths of a material at the design temperature for 100 thousand hrs in a creep test. The creep limit of a material at a creep rate of 1% at the design temperature for 100 tousand hrs in a creep test.