3.3plain material and welded joints

In plain material and welded joints, the range of stress due to the applied cyclic loads shall not exceed the allowable stress range computed as follows.

• (a) For stress categories A, B, B′, C, D, E, and E′, the allowable stress range, FSR, shall be determined by Equation A-3-1 or A-3-1M, as follows:

(A-3-1)

(A-3-1M)

where

$C_{f}$ = constant from Table A-3.1 for the fatigue category

$F_{S R}=$ allowable stress range, ksi (MPa)

$F_{T H}=$ threshold allowable stress range, maximum stress range for indefinite design life from Table A-3.1, ksi (MPa)

$n_{S R}=$ number of stress range fluctuations in design life

• (b) For stress category F, the allowable stress range, $F_{S R}$, shall be determined by Equation A-3-2 or A-3-2M as follows:

(A-3-2)

(A-3-2M)

• (c) For tension-loaded plate elements connected at their end by cruciform, T-, or corner-joint details with partial-joint-penetration (PJP) groove welds transverse to the direction of stress, with or without reinforcing or contouring fillet welds, or if joined with only fillet welds, the allowable stress range on the cross sec- tion of the tension-loaded plate element shall be determined as the lesser of the following:
• (1) Based upon crack initiation from the toe of the weld on the tension-loaded plate element (i.e., when $R_{P J P}=1.0$ ), the allowable stress range, $F_{S R}$, shall be determined by Equation A-3-1 or A-3-1M for stress category C.
• (2) Based upon crack initiation from the root of the weld, the allowable stress range, $F_{S R}$, on the tension loaded plate element using transverse PJP groove welds, with or without reinforcing or contouring fillet welds, the allowable stress range on the cross section at the root of the weld shall be determined by Equation A-3-3 or A-3-3M for stress category $C^{\prime}$ as follows:

(A-3-3)

(A-3-3M)

where

$R_{P J P}$, the reduction factor for reinforced or nonreinforced transverse PJP groove welds, is determined as follows:

(A-3-4)

(A-3-4M)

• $\begin{aligned} 2 a & =\text { length of the nonwelded root face in the direction of the thickness of } \\ & \text { the tension-loaded plate, in. (mm) }\end{aligned}$
• $t_{p}=$ thickness of tension loaded plate, in. (mm)
• $w=$ leg size of the reinforcing or contouring fillet, if any, in the direction of the thickness of the tension-loaded plate, in. (mm)

If $R_{P J P}=1.0$, the stress range will be limited by the weld toe and stress category C will control.

• (3) Based upon crack initiation from the roots of a pair of transverse fillet welds on opposite sides of the tension loaded plate element, the allowable stress range, $F_{S R}$, on the cross section at the root of the welds shall be determined by Equation A-3-5 or A-3-5M, for stress category C" as follows:

4.4 0.333 FSR 1,000RFIL (A-3-5) nSR

(A-3-5M)

where

$R_{FIL}$ = reduction factor for joints using a pair of transverse fillet welds only $=\frac{0.06+0.72\left(w/t_{p}\right)}{t_{p}^{0.167}}\leq1.0$ (A-3-6) $=\frac{0.103+1.24\left(w/t_{p}\right)}{t_{p}^{0.167}}\leq1.0$ (A-3-6M)

If RFIL = 1.0, the stress range will be limited by the weld toe and stress cate- gory C will control.

User Note: Stress categories C' and C" are cases where the fatigue crack initiates in the root of the weld. These cases do not have a fatigue threshold and cannot be designed for an infinite life. Infinite life can be approximated by use of a very high cycle life such as $2 \times 10^{8}$. Alternatively, if the size of the weld is increased such that $R_{F I L}$ or $R_{P J P}$ is equal to 1.0, then the base metal controls, resulting in stress category C, where there is a fatigue threshold and the crack initiates at the toe of the weld.