GENERAL

This IM covers the requirements of zinc coating (galvanizing) by the hot dip process on iron and steel products made from rolled pressed and forged shapes, castings, plates, bas, and strips.

Also this IM covers the requirements for hot dip zinc coating and mechanically zinc deposited on fasteners and anchor bolts.

HOT DIP GALVANIZED COATINGS ON IRON AND STEEL PRODUCTS

A. MATERIALS AND FABRICATION

1. Steel and Iron – the grade, specification, designation type and degree of surface contamination of the iron or steel in articles and items to be galvanized shall be supplied by the fabricator to the galvanizer prior to the galvanizing process.

2. Communication and / or consultation between the fabricator and galvanizer at appropriate stages in the fabrication process may reduce the occurrence of potential future problems. Also communication between the fabricator, the galvanizer, and the paint shop shall be required to avoid the occurrence of potential future problems.

3. Bath composition – the molten metal of galvanizing bath shall contain not less than an average value of 98% zinc by weight.

4. Coating thickness

a. Minimum of five test measurements on a specimen shall be taken.

b. The average thickness of coating for all specimens tested shall conform to the requirements of ASTM A 123 for the specified categories and thickness.

c. Coating thickness grade (as specified by ASTM A 123 and / or as specified in the contract documents.

Minimum Average Coating Thickness Grade per ASTM A 123
Material Category	1/16”	1/16” to 1/8”	1/8” to 3/16”	3/16” to 1/4”	>1/4”
Structural Straps & Plates	45	65	75	75	100
Pipes & Tubing	45	45	75	75	75
Strips & Bars	45	45	75	75	100
Wire	45	65	75	75	80
Reinforcing Bars	35	50	60	65	100

Coating Thickness Grade per ASTM A 123 / A 123 M
Coating Grade	Mils	Oz / Ft²	µm	g/m²
35	1.4	0.8	35	245
45	1.8	1.0	45	320
50	2.0	1.2	50	355
55	2.2	1.3	55	390
60	2.4	1.4	60	425
65	2.6	1.5	65	460
75	3.0	1.7	75	530
80	3.1	1.9	80	565
85	3.3	2.	85	600
100	3.9	2.3	100	705

5. All sharp edges shall be rounded up (to near 1/16”) prior to galvanizing.

a. Appearance – galvanized articles and / or items shall be free from uncoated areas, blisters, flux deposits, lumps, projections, globules (bubbles or tiny balls) and / or heavy deposits of zinc which will interfere with the intended use of the items, shall not be acceptable.

b. High spots and rough edges such as the metal drip line shall be removed until it is level with the surrounding area, taking care that the base coating is not removed.

c. Holes of ½” in diameter and larger shall be cleaned free from excess zinc.

6. Thickness coating test – the thickness coating shall be determined by one or several methods

a. Magnetic Thickness Gage (most common in the field and in the lab)

b. Stripping method

c. Weighing before and after galvanizing

7. Certification

The galvanizer shall furnish certification to the Iowa Department of Transportation certifying that samples representing each lot have been either inspected and / or tested as required by the specification and also by ASTM A 123 and that the requirements of the ASTM and the Iowa DOT have been satisfied.

8. Adherence

The zinc coating shall withstand handling consistent with the nature and thickness of the coatings and normal use of the items or article, without flaking or peeling which are grounds for rejection.

Zinc Coatings of Alloy Steel Bolts, Anchor Bolts, Nuts,

Washers, and Special Threaded Fasteners:

Fasteners can only be galvanized by either of these two processes

Mechanically galvanized ASTM B 695 Class 55 and/or galvanized to the requirements of ASTM F 2329. This process requires the removal of excess zinc by spinning the parts in a centrifuge, or brushing the threaded portion or handling otherwise to remove the excess zinc.

The maximum temperature of hot bath cannot exceed 850º F. Galvanizing carried out at a temperature above 850º F can adversely affect the final mechanical properties of fasteners. Therefore when galvanizing to the requirements of F 2329 the galvanizer shall provide a certified report indicating the hot zinc bath temperature and complete compliance with the ASTM requirements of(F 2329).

Dual zinc certifications such as A153/F2329 shall not be acceptable and shall be grounds for rejection.

GALVANIZED (Zinc) COATINGS

All threaded components (bolts, nuts, and anchor bolts) shall be coated by the same zinc coating process. No mixed processes in a lot shall be allowed.
Hot dip washers tend to bond to each other. Delivered galvanized washers shall not be bonded to each other. Bonded washers shall be rejected.
The zinc coating on all type of fasteners shall be smooth and uniform in thickness. The coated fasteners shall be free from uncoated areas, blisters, flux deposits, lumps, and any type of projections that would interfere with the intended use of the fasteners and / or any defects not consistent with good galvanizing practice.
The zinc coating thickness shall be uniform inside and outside of pipes, tubes, poles and/or certain tanks. Inaccessible surface areas shall receive special attention from the galvanizer with surface preparation and zinc coatings.
It is the responsibility of the galvanizer to ensure compliance with the specifications and the requirements of the ASTM (B695 Class 55, F2329 and A123).

CERTIFICATION

The galvanizer shall certify to the state of Iowa that the samples representing each lot have been tested and inspected as required by the intended specification and that the requirements have been met. Additionally, the galvanizer shall report the average galvanizing temperature (when galvanizing fasteners is performed to the requirements of ASTM F 2329) and the average coating thickness of the production lot shall be furnished.

SHIPPING AND HANDLING

Articles and fasteners that are galvanized shall be protected from any damage to the coating, surface finish and appearance.