FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 4. Metal Structure, Welding, and Brazing | 1. Identification of Metals | 4-3. Interchangeability of Steel Tubing
AC 43.13-1B CHG 1
9/27/01
b. There are numerous steels with higher
percentages of alloying elements that do not fit
into this numbering system. These include a
large group of stainless and heat resisting al
loys in which chromium is an essential alloy
ing element. Some of these alloys are identi
fied by three digit AISI numbers and many
others by designations assigned by the steel
company that produces them. The few exam
ples in table 4-3 will serve to illustrate the
kinds of designations used and the general al
loy content of these steels.
c. “1025” welded tubing as per Specification
MIL-T-5066 and “1025” seamless tubing con
forming to Specification MIL-T-5066A are inter
changeable.
4-3. INTERCHANGEABILITY OF
STEEL TUBING.
a. “4130” welded tubing conforming to
Specification MIL-T-6731, and “4130” seam-less
tubing conforming to Specification MIL-T-6736
are interchangeable.
b. NE-8630 welded tubing conforming to
Specification MIL-T-6734, and NE-8630
seamless tubing conforming to Specification
MIL-T-6732 are interchangeable.
4-4. IDENTIFICATION OF ALUMINUM.
To provide a visual means for identifying the
various grades of aluminum and aluminum
alloys, such metals are usually marked with
symbols such as a Government Specification
Number, the temper or condition furnished, or
the commercial code marking. Plate and sheet
are usually marked with specification numbers
or code markings in rows approximately
5 inches apart. Tubes, bars, rods, and extruded
shapes are marked with specification numbers
or code markings at intervals of 3 to 5 feet
along the length of each piece.
The commercial code marking consists of a
number which identifies the particular compo
sition of the alloy. In addition, letter suffixes
(see table 4-4) designate the basic temper des
ignations and subdivisions of aluminum alloys.
TABLE 4-2. Numerical system for steel identification.
TYPES OF STEELS
Plain carbon steel
Carbon steel with additional sulfur for easy
machining.
Carbon steel with about 1.75% manganese
.25% molybdenum.
1% chromium, .25% molybdenum
2% nickel, 1% chromium, .25% molybdenum
1.7% nickel, .2% molybdenum
3.5% nickel, .25% molybdenum
1% chromium steels
1% chromium, 1.00% carbon
1.5% chromium steels
1.5% chromium, 1.00% carbon
1% chromium steel with .15% vanadium
.5% chromium, .5% nickel, .20% molybde-
num
.5% chromium, .5% nickel, .25% molybde-
num
2% silicon steels, .85% manganese
3.25% nickel, 1.20% chromium, .12% mo-
lybdenum
NUMERALS
AND DIGITS
10XX
11XX
13XX
40XX
41XX
43XX
46XX
48XX
51XX
51XXX
52XX
52XXX
61XX
86XX
87XX
92XX
93XX
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