FABRICATING GUIDELINES

Process: Alkaline clean, Rinse, Acid clean (pickle), Rinse, Flux, Dry, Galvanize, Water quench or chromate (optional)

It is important to maximize the corrosion protection by allowing the flow of molten zinc into and out of all parts of the fabricated Steel. The following guidelines are necessary conditions for the safety of the galvanizers and those who work in a galvanizing plant, and to ensure a free flow of molten zinc within the fabrication, thus giving a better quality finish.

If these guidelines are not met, air and or water trapped within a fabricated steel will be converted into superheated steam and can develop a pressure of up to 26.2mPa (3800 p.s.i.) when dipped into molten zinc at 455oC.

The following will explain design rules that will ensure the highest quality galvanizing, at the lowest price, with the maximum safety to our crew. Molten zinc must be able to free flow without blockage, thus openings must be large enough – without blockage of the structural strength – for zinc to flow into and out of the fabricated steel.

Fabricators should first check with your local Galvanizing Association (AGA –American Galvanizing Association) member, before work goes to completion, to ensure that drains and vents are located in the appropriate locations and are the correct size. Some steel projects may need to be double dipped due to their length.

Drain & Vent hole sizes (min) for various hollow sections

The drain and vent hole size represent the minimum acceptable and it is preferred that the full tube cross section be provided.
The table is also applicable to hollow sections fabricated from channels and angles, etc. Use the table with the appropriate outside dimensions of the boxed sections.
For larger sections use the associated table for tanks.
Should the recommended hole size be unacceptable contact your local GANZ member for further advice.
Lifting eyes to be provided for the hanging of steel work (adjacent same side as vent holes or provide holes for lifting wires).

REF.No.	HOLLOW SECTION TYPE & SIZE				MINIMUM VENT & DRAIN HOLE SIZE (DIA)
	CIRCULAR H.S		SQ. H.S	RECTANGULAR. H.S	MINIMUM VENT & DRAIN HOLE SIZE (DIA)
	NOMINAL BORE	OUTSIDE DIAMETER	OUTSIDE DIMN'S	OUTSIDE DIMN'S	VENT	DRAIN
	mm	mm	mm		mm	mm
1	8	13.5
2	10	17.5
3	15	21.3	13 x 13
4	20	26.9	16 x16
5	25	33.7	19 x 19
6	32	42.4	25 x 25	38 x 19	8	8
7	40	48.3	32 x 32	38 x 25
8	50	60.3	38 x 38	51 x 25
9	65	76.1	51 x 51	64 x 38, 76 x 38
10	80	88.9	64 x 64	76 x 51, 89 x 38
11	100	114.3	76 x 76
12			89 x 89
13				102 x 51, 102 x 76	12	12
14				127 x 51, 127 x 64	12	12
15	125	139.7	102 x 102	127 x 76, 152 x 76	16	16
16	150	165.1	127 x 127	152 x 102	25	25
17	200	219.1	152 x 152	203 x 102, 203 x 152	32	32
18	250	273.0	203 x 203	254 x 152	63	63
19	300	323.9	254 x 254	305 x 203	75	75
20	350	355.6	305 x 305	305 x 254	88	88
21	400	406.4			100	100

Tubular fabrications and hollow structures

Tubular assemblies such as handrail, pipe columns, pipe girders, steel light poles, transmission poles, pipe trusses, and sign bridges are commonly galvanized.

Cleaning

As with all steel to be galvanized, pipe, R.H.S. and other hollow materials must be thoroughly cleaned before the molten zinc will allow the steel to produce the galvanizing coating inside and out.

R.H.S. and pipe commonly presents two special cleaning problems:

The "mill coating" (varnish, lacquer, 'black Japan' and similar materials) applied by the manufacturer costs extra to remove at the galvanizing plant.
Use only water soluble cutting fluids when drilling to avoid steel contamination that may incur extra cleaning costs.

Venting

IT IS MANDATORY that tubular fabrications and hollow structural's be properly vented.
Refer to Fig. 2.

ANY PICKLING ACIDS OR RINSE WATERS THAT MIGHT BE TRAPPED IN A BLIND OR CLOSED JOINT CONNECTION WILL BE CONVERTED TO SUPER-HEATED STEAM AND CAN DEVELOP PRESSURE OF UP TO 26.2Mpa (3800 psi) WHEN IMMERSED IN MOLTEN ZINC AT 455 DEGREES CELCIUS. THIS IS A SERIOUS POTENTIAL HAZARD TO GALVANIZING EQUIPMENT AND TO PERSONNEL.

Proper galvanizing demands that inside, as well as outside, be completely cleaned and coated with zinc - air and ash must be allowed to flow UPWARD AND COMPLETELY OUT, CLEANING SOLUTIONS AND MOLTEN ZINC MUST BE ALLOWED TO FLOW IN AND COMPLETELY WET SURFACES.

In all tables of draining, venting and gusset bevel calculations, allowance has been made for the speedy and total expulsion of entrapped air and ash produced during the galvanizing process.

Simply stated, the structure must be lowered into the solution without trapping any air. It must be raised from the solution without trapping any solution. Consequently, ample passageways that allow flow in and out must be designed into the assemblies.

SINCE ITEMS TO BE GALVANIZED ARE IMMERSED AND WITHDRAWN AT AN ANGLE, THE VENT HOLES SHOULD BE LOCATED AT THE HIGHEST POINT AND DRAINAGE HOLES AT THE LOWEST POINT IN EACH HOLLOW MEMBER.
Refer Fig. 1.

Aspects of internally drilling components for galvanizing (like handrails)

All components of fabricated hollow sections should be inter-connected with full open tee or with mitered joints. Each closed section must be provided with a vent hole and a drain hole.

Most galvanizers prefer to visually identify the venting from the outside when assembly is received. This is necessary to check the adequacy of venting as well as to determine that it has not been omitted by mistake.

YOUR GALVANIZER MUST BE NOTIFIED IN WRITING IF FABRICATIONS ARE INTERNALLY VENTED.

Base plates and end plate must be designed to facilitate venting and draining. Fully cutting the plate provides minimum obstruction to a full, free flow into and out of hollow sections. Since this is not always possible, the use of vent holes in the plate often provides a solution.

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