A153 specification covers zinc coatings applied by the
hot-dip process on iron and steel hardware. The hot-dip
galvanizing process consists of parts being immersed in molten
zinc for a sufficient time to allow a metallurgical reaction
between iron from the steel surface and the molten zinc,
resulting in the formation of Zn/Fe alloy layers bonding the
coating to the steel surface.
This specification is intended to be applicable to hardware items that are centrifuged or otherwise
handled to remove
excess galvanizing bath metal (free zinc). Coating thickness
grade requirements reflect this.
Steel or Iron-Ferrous articles to be hot-dip zinc coated
shall conform to specifications designated by the purchaser.
Zinc—The zinc used for the coating shall conform to
Specification B6, or Specification B960, or both,
and shall be
at least equal to the grade designated as “Prime Western.”
If a zinc alloy is used as the primary feed for the
galvanizing bath, then the base material used to make that alloy
shall conform to Specification B6 or Specification B960, or
both.
The molten metal in the working volume of the
galvanizing bath shall contain not less than an average value of
98.0 % zinc by weight [mass].
Note 1 -The galvanizer may choose to add trace amounts of certain
elements (for example, aluminum, nickel, bismuth, or tin) to the zinc bath
to help in the processing of certain reactive steels or to enhance the
cosmetic appearance of the finished product. The elements can be added
to the galvanizing bath as a master feed alloy, or they can be added to the
bath by the galvanizer as individual feeds.
Minimum Coating Weight [Mass] or Minimum Coating
Thickness—The minimum coating weight [mass] or the minimum coating thickness shall conform to the
requirements
prescribed in Table 1 for the material category and thickness of
material in which the article belongs.
Threaded Articles—The zinc coating on threads shall
not be subjected to a cutting, rolling, or finishing-tool
operation, unless specifically authorized by the purchaser. In
order to meet overtapping allowances, tapping the threads of
nuts or tapped holes after galvanizing is not prohibited.
Touch-up and Repair—Bare spots that are found on
parts after galvanizing shall be renovated by use of the methods
found in Practice A780 if the following criteria are met. The
bare spots shall have an area totalling not more than 1 % of the
surface area to be coated excluding threaded areas of the piece
and the bare spots shall not include any threaded areas of the
piece. The thickness of the repair shall be equal to the
surrounding galvanized coating except for repairs made by
paints containing zinc dust in which case the thickness of the
repair shall be 50 % greater than the thickness of the galvanized coating required for the class of
material, but shall not be greater than 4.0 mils [100 µm]. Repair thickness measurements
shall be made in accordance with Practice A780. The galvanizer shall make repairs unless directed by the
purchaser to
deliver items unrepaired for subsequent renovation by the
purchaser.
Note - Length of the piece, stated in Classes B-1, B-2, and B-3, refers to the finished dimension of the piece after fabrication.
| Class of Material | Weight [Mass] of Zinc Coating, oz/ft 2 [g/m2 ] of Surface, Minimum |
Coating Thickness, mils [microns], Minimum |
||
|---|---|---|---|---|
| Average of
Specimens Tested |
Any
Individual Specimen |
Average of
Specimens Tested |
Any
Individual Specimen |
|
| Class A—Castings—Malleable Iron, Steel Class B—Rolled, pressed, and forged articles (except those which would be included under Classes C and D): | 2.00 [610] | 1.80 [550] | 3.4 [86] | 3.1 [79] |
| B-1—5⁄8 in. [15.88 mm] and over in thickness and over 15 in. [381 mm] in length | 2.00 [610] | 1.80 [550] | 3.4 [86] | 3.1 [79] |
| B-2—under 5⁄8 in. [15.88 mm] in thickness and over 15 in. [381 mm] in length | 1.50 [458] | 1.25 [381] | 2.6 [66] | 2.1 [53] |
| B-3—any thickness and 15 in. [381 mm] and under in length | 1.30 [397] | 1.10 [336] | 2.2 [56] | 1.9 [48] |
| Class C—Fasteners over 3⁄8 in. [9.52 mm] in diameter and similar articles. Washers 3⁄16 in. and greater [4.76 mm and greater] in thickness | 1.25 [381] | 1.00 [305] | 2.1 [53] | 1.7 [43] |
| Class D—Fasteners 3⁄8 in. [9.52 mm] and under in diameter, rivets, nails and similar articles. Washers under 3⁄16 in. [4.76 mm] in thickness | 1.00 [305] | 0.85 [259] | 1.7 [43] | 1.4 [36] |
The zinc-coated articles shall be free from uncoated
areas, blisters, flux deposits, dross inclusions, and other types
of projections that would interfere with the intended use of the
articles, or other defects not consistent with good galvanizing
practice.
The zinc coating shall be reasonably smooth and uniform in thickness.
Note 2—Smoothness of surface is a relative term. Minor roughness
that does not interfere with the intended use of the part, or roughness that
is related to the as-received (ungalvanized) surface condition of the part,
shall not be grounds for rejection.
Note 3 —Since this specification is applicable to items that are
centrifuged or otherwise handled to remove excess bath metal (see 1.2),
irregular coating distribution is not normally encountered. Drainage
problems, which manifest themselves as local excess coating thickness
that would interfere with function or as edge tears or spikes that present
a safety hazard because of their sharpness, are grounds for rejection under
the terms of 5.1.
Embrittlement is a potential condition of steel that is
cold-worked, depending on such factors as the steel type
(strength level, aging characteristics), thickness, degree of cold
work, and galvanizing process. The galvanizer, the designer
and the fabricator shall take precautions against embrittlement.
The precautions to fabricate properly and prepare the material
for galvanizing to prevent embrittlement are described in
Practice A143/A143M.
Note 4 —Low service temperatures increase the risk of brittle failure of
all plain carbon steels including those which have been galvanized. This
temperature embrittling effect varies with type of steel. The expected
service temperature should thus be taken into account when selecting
steels for galvanizing.
Malleable castings shall be of such composition as will
preclude the possibility that they become embrittled by the
galvanizing process, or they shall be either cooled from the
anneal, or subsequently heat-treated so as to immunize them
against embrittlement.
The zinc coating shall adhere tenaciously to the surface
of the base metal.
If the galvanized material covered by this specification
is bent or otherwise fabricated to the degree that causes the zinc
coatings to stretch or compress beyond the limit of elasticity,
any cracking or flaking of the coating resulting from the
bending or fabricating shall not be cause for rejection.
High strength bolts, typically over 150,000 lb/in.2 ultimate tensile strength, may be subject to
hydrogen embrittlement. Practices to safeguard against hydrogen embrittlement
are described in Specification A143/A143M.
Test specimens shall be selected at random from each
inspection lot.
The method of selection and sample size shall be agreed
upon between the galvanizer and the purchaser. Otherwise, the
sample size selected from each lot shall be as follows:
| Number of Pieces in Lot | Sample Size |
|---|---|
| 3 or less | all |
| 4 to 500 | 3 |
| 501 to 1200 | 5 |
| 1201 to 3200 | 8 |
| 3201 to 10 000 | 13 |
| 10001 and over | 20 |
A specimen that fails to conform to a requirement of this
specification shall not be used to determine the conformance to
other requirements.
The method of sampling for fasteners that are required
to meet the standards of the Fastener Quality Act is described
in Guide F1470. Sample quantities and definitions of terminology are included in the referenced
specification.
Tests shall be made to ensure that the zinc coating is
being furnished in accordance with this specification and as
specified for the following:
Minimum coating weight [mass] or minimum coating
thickness in 4.3.
Finish and appearance in 5.1 and 5.2.
Embrittlement in 5.3 and 5.4.
Adherence in 5.5.
Average Weight [Mass] of Coating:
The average weight [mass] of the zinc coating shall be
determined by weighing specimens after pickling and drying
and again after galvanizing unless the method described in
7.2.2 is used. The number of specimens that are used to
determine the average of an inspection lot shall be derived
from Section 6.
Note 5 —This method does not take into account the weight [mass] of
iron reacted from the article that is incorporated into the coating. It will
thus underestimate coating weight [mass] by up to approximately 10 %.
Base metal reactivity will affect the extent of underestimation.
In the case of materials inspected after galvanizing,
the average weight [mass] of coating shall be determined by
stripping the number of specimens derived in Section 6 in
accordance with Test Method A90/A90M, and averaging the
results of the individual specimens, unless the method described in 7.2.1 is used.
Average Thickness of Coating:
In the case of fasteners such as bolts, nuts, and screws,
the determination of the thickness of coating shall be made on
a portion of the article that does not include any threads.
The average thickness of coating shall be determined
by magnetic thickness gage in accordance with Practice E376
unless the method described in 7.3.3 is used. The thickness
shall be measured on at least five widely separated spots on a
specimen. No individual spot measurement shall be cause for
rejection. If an individual spot does not provide a coating
thickness reading, this spot must be repaired in accordance
with 4.5. The five or more individual coating thickness
measurements on a specimen must be averaged to determine
the specimen average coating thickness. The average coating
thickness for the inspection lot is determined by averaging the
specimen average coating thickness values for the number of
specimens derived from Section 6.
The thickness of coating shall be determined by cross
section and optical measurement in accordance with Test
Method B487, unless the method described in 7.3.2 is used.
The thickness thus determined is a point value. No less than
five such measurements shall be made at locations on the
specimen, which are as widely dispersed as practical, so as to
be representative of the whole surface of the specimen. The
average of no less than five such measurements is the specimen
average coating thickness. The average coating thickness for
the inspection lot is determined by averaging the specimen
average coating thickness values for the number of specimens
derived from Section 6.
Finish and Appearance—The test for finish and appearance shall be conducted through visual
inspection without
additional magnification.
Embrittlement—Hardware that is susceptible to embrittlement shall be tested in accordance with
Practice A143
A143M. The tests shall be performed through agreement
between the galvanizer and the purchaser.
Adherence—Determine adherence of the zinc coating to
the surface of the base metal by cutting or prying with the point
of a stout knife, applied with considerable pressure in a manner
tending to remove a portion of the coating. The adherence shall
be considered inadequate if the coating delaminates in the form
of a layer of skin so as to expose the base metal in advance of
the knife point. Do not use testing carried out at edges or
corners (points of lowest coating adherence) to determine
adherence of coating. Likewise, do not use removal of small
particles of the coating by paring or whittling to determine
failure.
The inspector representing the purchaser shall have access at all times while work on the contract of the purchaser is being performed, to those areas of the manufacturer’s work which concern the application of the zinc coating to the material ordered. The manufacturer shall afford the inspector all reasonable facilities to satisfy him that the zinc coating is being furnished in accordance with this specification. All inspection and tests shall be made at the place of manufacture prior to shipments, unless otherwise specified, and shall be so conducted as not to interfere unnecessarily with the operation of the works.
For all galvanized articles except those fasteners that
must meet the requirements of the Fastener Quality Act, the
following sections are used to determine rejection and retesting.
When partial inspection of materials to determine conformity with visual requirements of Section 5
warrants rejection of a lot, the galvanizer is not prohibited from sorting the
lot and submitting it once again for inspection.
The number of specimens in a sample of a lot permitted
to fail to conformance tests shall be agreed upon between the
galvanizer and the purchaser.
If a set of test specimens fails to conform to the
requirements of this specification, two additional sets shall be
tested, both of which shall conform to the requirements in
every respect, or the lot of material represented by the
specimens shall be rejected.
Materials that have been rejected for reasons other than
embrittlement are not prohibited from being stripped,
regalvanized, and resubmitted for test and inspection. They
shall then conform to the requirements of this specification.
Note 6 —Conformance to this specification does not guarantee “zero
defects.” Depending on the size and configuration of the parts (small
diameter threaded parts and small washers as examples), a small amount
of “fall out” may exist in an inspection lot that is not detected during a
sample inspection. Issues include, but are not limited to, zinc build up in
the threads or bonded washers. Handling of these types of issues need to
be negotiated between the purchaser and supplier.
ASTM Standards:
A90/A90M Test Method for Weight [Mass] of Coating on
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
A143/A143M Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel
Products and
Procedure for Detecting Embrittlement
A780 Practice for Repair of Damaged and Uncoated Areas
of Hot-Dip Galvanized Coatings
A902 Terminology Relating to Metallic Coated Steel Products
B6 Specification for Zinc
B487 Test Method for Measurement of Metal and Oxide
Coating Thickness by Microscopical Examination of
Cross Section
B960 Specification for Prime Western Grade-Recycled
(PWG-R) Zinc
E376 Practice for Measuring Coating Thickness by
Magnetic-Field or Eddy-Current (Electromagnetic) Testing Methods
F1470 Practice for Fastener Sampling for Specified Mechanical Properties and Performance Inspection
F1789 Terminology for F16 Mechanical Fasteners
The supplier shall employ such methods of packaging zinc-coated articles as shall be required to ensure their receipt by the purchaser in satisfactory condition, with the use to be made of the article being taken into consideration.