Engineering

For a given working load, how large should the bolt be? This article covers the preliminary design and pre-selection of bolts: first read the nominal diameter and property class from a quick pre-selection table by load range, then use the Kübler equation to back out the thread stress cross-section from the axial working load and the required clamping force, combined with the tightening factor, reduction factor and simplified fatigue and bearing-pressure checks, to help engineers quickly size a bolt in the early design stage.

The bolted joint is one of the most widely used connection methods in mechanical engineering. Starting from the inclined-plane nature of a thread, this article sets out thread geometry and classification: the lead angle, the pitch, the pitch diameter d2, the minor diameter d3 and other key geometry parameters; common thread profiles and technical standards such as metric ISO coarse/fine, pipe threads and trapezoidal threads; and the functional distinction between fastening bolts, motion screws and sealing/adjusting bolts — laying the geometric groundwork for the later bolt strength calculation and pre-selection.

A walkthrough of the latest ASME BPVC Section XI Appendix Y models for fatigue crack growth and stress-corrosion cracking in austenitic, ferritic and nickel-base alloys, with a code-based online calculation guide.

How KTA 3206 treats fatigue crack growth in a Leak-Before-Break (LBB) argument: the Paris-Erdogan equation in the steady-state region, constants for ferritic and austenitic steels, the NUREG/CR-6176 term for high-temperature water, and a worked example.

Walks through the KTA 3206 seven-step method for break exclusion of nuclear piping: initial crack, fatigue growth, critical through-wall crack length, critical surface crack depth, detectable crack length, allowable crack size and the LBB verdict.

An introduction to Leak-Before-Break (LBB): what it means, where it applies and where it does not, the main codes, the three analysis steps, and a nuclear piping example.