XIII.
SPECIFICATIONS.
Specifications should cover three principal points:
Physical properties: Elastic limit; ultimate tensile strength; elongation; reduction of area.
Chemical constituents: Limiting silicon, phosphorus, sulphur, manganese, and copper; all other elements to be absent or mere traces in quantity, except carbon.
Finish and general condition: Fixing limit of variation in size from a given standard; conditions as to pipes, seams, laps, uniformity of grain, and other defects; no red-shortness.
PHYSICAL PROPERTIES.
It has been shown in [Chap. V] that tensile strength may be had from 46,800 lbs. per square inch to 248,700 lbs. per square inch.
There are published in many transactions and technical periodicals thousands of tests giving elastic and ultimate strength, ductility, etc., so that every engineer can find easily what has been done to guide him as to what he can get.
In almost every case the engineer must be the judge as to the requirements in each; therefore it would be useless to attempt to lay down any fixed rules or limits.
Many engineers adhere to low tenacity and high ductility in the belief that they are securing that material which will be safest against sudden shocks and violent accidental strains.