Weldability by the Numbers

About this book

Most welding training starts with mild steel, and for good reason: it is forgiving. It conducts heat moderately, expands moderately, melts its own oxide, and in its common grades it does not harden much when it cools quickly. Then a maintenance job arrives in a metal that behaves differently. A cast iron housing cracks again beside the repair. An aluminium cover fills with pores. A copper joint will not melt however long the flame plays on it. A nickel weld cracks for no visible reason. Each of those failures follows from a few physical properties that can be looked up, compared and planned for.

This book is for the people who make those decisions: maintenance and manufacturing engineers, welding supervisors, fabricators and inspectors. It assumes basic familiarity with welding processes and with simple algebra and SI units. It does not teach welding technique; that comes from qualified instruction and supervised practice. It explains why each metal needs the treatment it does, with numbers, so that a repair plan can be reasoned through and checked rather than copied from habit.

A 1915 handbook as the starting point

Autogenous Welding and Cutting, by Theodor Kautny of Nürnberg, was published in English by McGraw-Hill in 1915, translated by the author and James F. Whiteford. Kautny was closely involved with the welding schools then attached to Germany’s technical high schools, and his pocket book was written for works engineers, foremen and welders. Its first half covers gases, generators, burners and cutting, ground that READOS covers in Oxy-Fuel by the Numbers. Its second half takes each important metal in turn and explains how its nature governs welding.

Those chapters are the starting point here. Many of their insights still hold: carbon decides the character of iron; grey cast iron turns white and brittle if it loses silicon; aluminium’s oxide must be destroyed because it will not melt with the metal; copper absorbs gas and oxygen and is rescued by phosphorus; nickel has a dangerous affinity for sulphur. Some of the book’s figures are wrong by modern measurement, and some of its methods have been replaced. Kautny’s closing prediction, that joining metals below their melting point would transform many industries, came true seventy-six years later. Each chapter of this book restates one of his themes in modern terms, corrects it where needed and works it through a modern case.

The running case

This is an illustration. A regional maintenance workshop is rebuilding a cooling-water pump set for a food factory. The job brings together five metals:

• a grey cast iron pump casing, about 85 kg, with a 120 mm crack through a 25 mm mounting foot;
• a medium-carbon steel shaft, 60 mm in diameter, with a worn keyway to build up;
• a 6061-T6 aluminium cover plate, 400 × 300 × 10 mm, with a corroded boss to rebuild;
• a phosphorus-deoxidised copper cooling coil with a cracked joint at a 12 mm thick header block;
• a 316 stainless steel drain spool to be welded to a mild steel bracket on the baseplate.

Through the book each repair is planned from the metal’s properties, with the heat, expansion, composition and risk worked out. The workshop, the parts, compositions, dimensions, settings and results are invented for teaching. They are not KEVOS® work, and the compositions are rounded illustrations, not certified data for any material.

How to use the book

Chapters 1 to 3 build the general tools: which properties matter, how heat flows and how expansion and restraint create stress. Chapters 4 to 8 apply them to carbon steel, cast iron, aluminium, copper and nickel in turn. Chapter 9 deals with joining different metals, and Chapter 10 with solid-state joining, choosing a process and recording the repair. Every chapter ends with an exercise and its worked answer.

Limits and professional responsibility

This book is educational. Welding and repair of load-bearing, pressure-containing or safety-critical parts must follow qualified welding procedures, carried out by qualified welders and inspected as the applicable standards, codes and regulators require. Welding fume, including fume containing chromium, nickel, zinc, copper and lead, is a recognised health hazard, and work must follow Safe Work Australia’s model code of practice on welding processes as adopted in each jurisdiction, and the material and consumable suppliers’ safety data sheets. The 1915 methods are described as history, not practice. Physical properties are typical values from secondary tables and vary with alloy and temperature; certified data should be used for design.

An original treatment

READOS already covers steel plate repair in Weld Repairs That Hold and the oxy-fuel process in Oxy-Fuel by the Numbers. This book concentrates on the metals themselves. The explanations, the pump-set case, the calculations, figures and exercises are original KEVOS® writing. The 1915 handbook is a public-domain historical work in the United States; its ideas are summarised, discussed and corrected in new words, and none of its text, tables or illustrations is reproduced.