CEMP-E
TI 809-26
1 March 2000
form of the member (plate base metal, rolled section base metal, weld type),
location of anticipated crack initiation (base metal, weld, weld toe),
governing dimensions (attachment dimensions, radius of transition, weld length, etc.),
fabrication requirements (ground flush, backing removed, etc.), and
inspection requirements (ultrasonic or radiographic testing). The detail category should be
evaluated carefully to verify that the actual detail realistically matches the standard detail.
(4) Careful design and fabrication can reduce the risk of failure by fatigue. Not all methods of
fatigue life improvement are contained in the Codes, and not all methods are necessary. Smooth shapes
and transitions are important, but radiused transitions are expensive and may not substantially improve
fatigue life.
Grinding groove welds flush in the direction of the applied stress may improve the Stress
Category.
Avoid reentrant, notch-like corners.
Transitions between members of differing thicknesses or widths should be made with a
slope of at least 2.5:1.
Joints should be placed in low stress areas, when possible.
Groove-welded butt joints have better fatigue life than lap or tee joints made with fillet
welds.
Parts should be aligned to minimize or eliminate eccentricity and minimize secondary
bending stresses.
Avoid attachments to members subject to fatigue loading.
Attachment welds should be kept at least 12 mm (1/2 in.) from the edges of plates.
Welds on the edges of flanges should be avoided. Fillet welds should be stopped about 12
mm (1/2 in.) short of the end of the attachment, provided this will not have any other
detrimental effect on the structure.
If a detail is highly sensitive to weld discontinuities, such as a transversely loaded CJP
groove weld with reinforcement removed, appropriate quality, inspection, and NDT
requirements should be specified.
Fatigue life enhancement techniques such as those found in AWS D1.1 Section 8, may be
cost-effective in extending fatigue life.
When grinding is appropriate, grinding should be in the direction of stress.
Intermittent stitch welds should be avoided. Unauthorized attachments, often made by field
or maintenance personnel or other trades, must be prohibited.
A bolted assembly may be appropriate and more cost-effective in some applications.
For critical details, provide for in-service inspection.
b. Fatigue Design Details. Fatigue details are identified as plain material, built-up members, groove
welds, groove-welded attachments, fillet welds, fillet-welded attachments, stud welds, and plug and slot
welds. Further divisions of these general categories are provided using general descriptions, and in some
cases, by attachment length, radius, grinding requirements, NDT requirements, and member yield
strength. Illustrative examples are typically provided by the codes to assist in the interpretation of these
divisions.
(1) Stress Category A is limited to plain material, with no welding. Categories B, C, D and E follow
the same line slope, with reduced permitted stress ranges for a given fatigue life demand. Category F
behavior is sufficiently different to use a different slope. The endurance limit is also reached soonest, at
the highest stress range, for Category A details, with progressively more cycles and lower stress ranges
for the endurance limit in other categories.
5-10
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