HDGASA OC Rev 1

Fundamentals of the Hot Dip Galvanizing Process Online Course Welcome and Introduction Welcome to the Hot Dip Galvanizers Association’s (HDGASA) online training programme. We trust that you will find this learning experience both beneficial and exciting. This online course covers each step in the batch type / general hot dip galvanizing process. 1 Receiving and Inspection of articles before Hot Dip Galvanizing 2 Jigging 3 Degreasing and Rinsing 4 Acid Pickling and Rinsing 5 Flux and Drying 6 Water Quench, Passivating or Air Quenching 7 De-jigging, Fettling & Cleaning 8 Inspection, Packing & Despatch 9 Repair Procedures, Stripping & Re-galvanizing Dimensions and Symbols frequently used within the Hot Dip Galvanizing Industry Length and Thicknesses Lengths 1m = 100cm = 1 000mm Thickness 1/1000mm = 0.001mm = 1μm Note: American imperial – 1 mil =1/1000 inch = 25.4μm Area 10cm x 1cm = 10 cm2 10cm x 10cm = 100cm2 1m x 1m = 1m² = 100cm x 100cm =10 000cm2 Common Symbols µm = micron = 0.001 mm = 1/1 000mm < - less than also < - lowest single reading taken > - highest single reading taken > - greater than also n - number of individual readings taken < - less than or equal to – mean calculated from all readings taken ≥ - greater than or equal to pH number of a solution denotes an acid or alkaline pH = 7 Neutral pH < 7 Acidic pH > 7 Alkaline The Value Chain and Hot Dip Galvanizing Hot dip galvanizing is part of a value chain that starts at the steel mill and is finally used in a manufactured or fabricated article. It is therefore imperative to understand that the quality of the final HDG steel article starts even before an article arrives at the galvanizing facility. Throughout the value chain designers, fabricators and galvanizing personnel must work to all applicable standards to ensure the quality of the article finally put into service. Page 1 of 23

The Batch Type / General Hot Dip Galvanizing Process 1 STORAGE AREA Goods receiving & inspection PREPARATION (Drill holes, remove paint) GRIT BLASTING when required JIGGJIINGGGING HDGA022 DEGREASING 3 WATER RINSE PICKLING 4 WATER RINSE FLUX 5 DRYING BLOWING “DRY’ GALVANIZING “WET” GALVANIZING 6 (FLUX BLANKET) 6 ZINC GALVANIZING OPERATION WATER QUENCH 7 CENTRIFUGE 6 PASSIVATING DE-JIGGING, FETTLING & CLEANING OC 09 INSPECTION, PACKING & DESPATCH Fig 1: Hot dip galvanizing flow diagram, indicating variations found in different plants regarding a dry and wet process, centrifuge or automatic tube and pipe galvanizing Page 2 of 23

1. Receiving and Inspection of articles before Hot Dip Galvanizing 1.1 Incoming material for Hot Dip Galvanizing All incoming material is weighed in, as hot dip galvanizing is charged by mass. Paint on the other hand is charged per square metre of surface area. This pre-galvanized mass is known as the ‘Raw Mass’. After being weighed-in, the material is offloaded using appropriate handling equipment (overhead cranes or forklifts), accurately labelled and safely stacked while awaiting a pre- galvanizing acceptance inspection by the galvanizer’s quality control inspector. Material that passes the pre-galvanizing inspection is safely and securely stored. Later, the material will be attached, “jigged”, to the flight bars at the start of the HDG process. Material not fabricated to the needed fabrication standard will be quarantined. A notification will be sent to the customer regarding the issues for which the material was quarantined and further instruction from the customer are awaited. 1.2 Material handling equipment The following pictures are typical of a galvanizer’s handling equipment. Overhead bridge type cranes and flight bars are used throughout the galvanizing process. These cranes typically use twin hoists. Suitable suspending equipment for slinging and moving material from the incoming transport to the holding areas will include chains, nylon slings or specially designed stacking racks. When stacked the Page 3 of 23

material should be easily identifiable, including the customer’s details, order number and other pertinent information. 1.3 Safety Awareness in Hot Dip Galvanizing Plants It is appropriate to say that many hazards exist at a hot dip galvanizing facility. To avoid such hazards safety equipment, signage and instructions must be strictly adhered to within the galvanizing plant environment. Measures should include the use of appropriate personal protective equipment (PPE) for anyone entering a hot dip galvanizing facility. 1.4 Fundamentals of the Pre-Galvanizing Inspection Steel articles not designed in accordance with recommended HDG fabricating standards may give rise to potentially hazardous events. In the worst case an unvented article, when submerged in the molten zinc, at around 450oC, may explode. Apart from the destruction and extensive damage to the article and property, there is the danger of personnel being fatally or severely injured. The pre-galvanizing inspection seeks to ensure that articles received are able to be safely hot dip galvanized and have been fabricated accordingly. The following requirements and conditions highlight the need for correct fabrication in order to produce a quality HDG article: 1.4.1 Venting and Drainage All articles must be suitably vented to avoid entrapped air pockets which give rise to uncoated areas and/or entrap the molten zinc when removing the article from the zinc kettle. No Vent holes Page 4 of 23

Fabricated structures should have the corners cropped to allow for the free flow and drainage of zinc during the dipping process. 1.3.1. Welds and associated conditions All welds must to be free from weld slag and welding flux. Weld splatter must be at a minimum and findings clearly noted on the acceptance report. 1.4.2 Surface contamination Page 5 of 23

No paint or fabrication markers (other than water- soluble-paint based) should be present on the steel surface. The presence of heavy grease deposits or conditions such as mill scale will result in the material being quarantined. 1.4.3 Distortion and warpage potential Checks for indicators of potential distortion or warpage of incoming articles must be noted and the customer advised accordingly. Material which is mechanically damaged or distorted, as a result of welding, must be excluded from incoming material at the first opportunity prior to hot dip galvanizing. Page 6 of 23

Evidence of poor and sub-quality fabrication is photographed, quarantined and the customer notified of such conditions. Instructions from the customer are required before these items are removed from quarantine. 2.0 Jigging: Loading the Flight Bar Jigging is the first step in the HDG processing of steel and iron articles. Jigging focusses on correctly attaching these articles to a flight bar. Flight bars are lifted and moved with the use of an overhead crane. The flight bar is the singular element that transfers the steel articles between each stage of the HDG process. Five key elements relate to a correctly jigged flight bar. 2.1 Suitable attaching equipment In selecting the most suitable means of attaching an article to the flight bar, the following must be borne in mind: 2.1.1 Size, shape and mass of the article to be HDG. 2.1.2 Uniformity of material thickness and overall sizing. Page 7 of 23

2.2 Options Several attachment options vary from the use one or any combination of chains, hooks, wire, nylon slings or specially designed rigs. 2.2.1 Chains & Hooks 2.2.2 Nylon Slings 2.2.3 Wire Annealed wire (aka jigging wire) must meet strength and flexibility standards. Articles may require attachment to the flight bar by using wire in either single or multiples strands. Page 8 of 23

2.2.4 Specially designed Rigs Specifically designed rigs are used in many cases for standard products, repetitive in nature. The rigs are designed for standardised loads and to optimise the production throughput rate. Specially designed rigs must also be rated for a safe working load, managed in accordance with the OHSA and routinely inspected. 2.3 Attach Articles at a Suitable Angle Articles must be suspended at the steepest possible angle to the vertical, but not less than 45, to ensure adequate air venting and molten zinc drainage. Care must be taken in regard to the position of the venting and drainage holes in hollow products. The correct angle and number of suspension points also reduces the possibility of distortion (bending and twisting) when such inclined articles are dipped into the zinc melt. Page 9 of 23

2.4 Load the Flight Bar to SWL Capacity All Flight Bars must have a SWL limit, based on the crane lifting capacity, indicated in plain sight visible to all personnel. The Flight Bar must be loaded as close as practicable within the SWL to ensure the optimum use of resources. 2.5 Adhere to all Health and Safety requirements All rigs and handling equipment must be managed in accordance with the OHSA and be subject to routine safety inspections. All rigs and lifting equipment must have the Safe Working Load (SWL) clearly displayed and visible from the working positions and must be adhered to. All rigs and lifting equipment must be stored in a designated area and placed on suitably designed racks when not in use. OHSA requirements must be complied with from a registration and SWL testing regime. 3.0 Degrease and Water Rinse Degreasing and water rinse are the initial steps in the steel-cleaning process. Dirt, oil and light surface contamination is removed from the article. Jigged articles are submerged in a chemical (alkaline or acid) degreasing solution. A water rinse follows in order to check that degreaser has been effective and to avoid any alkali carry-over which will neutralize the acids in the pickling procedure. The effectiveness of subsequent stages of acid pickling as well as the hot dip galvanizing depend fundamentally upon how well the article has been degreased and water rinsed. Alkali degreasers consist of low concentration caustic solutions with a suitable wetting agent. Similar, suitably diluted, caustic soda alkali is found in commonplace cleaning agents in household soaps and surface cleaners. An uncommon alternative is acidic degreaser which consists of an hydrochloric acid a wetting agent and an acid inhibitor in solution. Degreasing solutions contain emulsifiers, to emulsify oils into sludge and liberate other oils that float to the surface. These are removed, normally by skimming to a grease trap and filtering. The degreasing process removes dirt and grease from the work prior to pickling The effectiveness of subsequent operations depends to a great extent on how well the articles are cleaned during this operation Page 10 of 23

4. Acid Pickling and Water Rinse The purpose of pickling prior to galvanizing is to remove mill scale, rust and other contaminants from the work. Pickling ensures that molten zinc comes into direct contact with all immersed steel surfaces during the hot dip galvanizing zinc melt thereby facilitating the formation of the zinc-iron alloys over the entire immersed surface area. Either Hydrochloric (HCl) acid or heated Sulphuric acid (H2SO4) can be used for this steel cleaning operation. Hydrochloric acid pickling is more commonly used in general galvanizing in South Africa. An HCl acid recycling process has been developed to regenerate / recycle hydrochloric acid. i SAFETY Operating staff should wear approved face shields, acid resistant aprons, rubber gloves, approved hard hats and safety boots or shoes when handling acid or working in the vicinity of acid tanks. Inhaling concentrated acid fumes is harmful. Climbing onto the sides of pickling tanks should be forbidden. Fresh water showers should be installed alongside pre- treatment tanks. If an operator or any other person is splashed with concentrated or dilute acid, the person should immediately wash or flush the affected portion of their body with running water. 4.1 Hydrochloric Acid parameters for effective pickling For pickling the HCl acid concentration is typically around 15%. At HCl levels above 15% there accumulates an excessive build-up of iron chlorides in the pickling bath, when iron chlorides reach a concentration level of 10%, the pickling solution must be discarded, regardless of acid concentration, since this level of iron renders the acid ineffective. For efficient and cost effective use of acids and associated chemicals, regular monitoring and chemical testing is essential. This can be achieved either by way of an in-house laboratory or by employing a reliable 3rd party service provider. Without using regular test results managing acid pickling bath procedures cannot be done properly. The purpose of cleaning and pickling prior to galvanizing, regardless of the acid or agent used, is to remove mill scale, rust and other contaminants from the work 4.1.1 Rinsing after pickling Best practices operations (BPO) for the pickled product requires that the pickled steel is completely immersed in a cold static water rinse and thereafter, immersed in a flowing water rinse. Page 11 of 23

5. Fluxing and drying Good fluxing practice improves coating appearance and quality. Furthermore it performs a key role in reducing zinc consumption during the zinc melt stage of hot dip galvanizing. Prior to fluxing, the article must be thoroughly cleaned and free from oxides, iron salts and any other surface contaminants. The film deposited by the flux solution protects the clean steel and prevents further oxidation. Additionally when dried flux comes into contact with molten zinc, the flux provides a final purgative action, which will remove any trace of oxides. Good fluxing practice is important to ensure a high quality coating from the standpoint of appearance, good adhesion and the absence of uncoated areas. 5.1 Flux Purification A suitable filter system will keep the flux clean by maintaining iron levels well below a 5% concentration level. Should a filtration system not be provided a process of regular purification by precipitation of the iron content by using hydrogen peroxide is available. 5.2 Drying Deck A drying deck is essentially a facility where fluxed articles are dried using heat, radiated by the zinc melt kettle, after being removed from the wet flux bath. Rapid drying is required for two reasons. Firstly it prevents iron salts and oxides from forming on the cleaned steel article before being hot-dipped. Secondly, if wet the moist film layer will cause explosions and molten zinc spatter when it contacts the hot zinc and turns to steam. In some plants, a drying oven is provided but the drying temperature must not be sustained at temperatures above about 80C as this will destroy the dry flux crystalized film. 6. Hot Dip Galvanizing Hot dip galvanizing cannot be achieved to any standard should the steel not be thoroughly cleaned before being submerged in the molten zinc. Each of the previous process steps, to clean the steel, is essentially pre-treatment for galvanizing. Simply put – IF THE STEEL IS NOT CLEAN IT WILL NOT GALVANIZE! Hot dip galvanizing is an honest coating in that a contaminated or dirty steel surface will not galvanize. Other coatings systems can be applied over contaminated or dirty surfaces. Trapped between the barrier layer and the steel corrosion development will lead to premature failure of the barrier coating undermining the estimated service life needed. This cannot occur with a hot dip Page 12 of 23

galvanizing barrier layer which is a barrier layer comprised of zinc iron alloys and some pure zinc on the outermost surface. The unbroken “barrier protective” layer of zinc and zinc iron alloys is a key element of all hot dip galvanizing standards. For general HDG a specified minimum mean thickness that complies with SANS 121:2011 (ISO 1461:2009) requirements is stipulated. Several appropriate standards for variations of the hot dip galvanizing process include continuous galvanizing: applied to sheet or wire, automatic or semi-automatic pipe and tube galvanizing and specific standards for hi-tensile fasteners and other High-Temperature HDG processes. 6.1 Metallic bonded coating When perfectly cleaned steel is immersed into molten zinc, a metallurgical reaction takes place, which forms zinc/iron alloys at the interface between the steel and the zinc. The coating formed is fairly complex and consists of various zinc /iron alloy phases (layers), namely: i. GAMMA phase - a thin layer at the steel interface which contains approximately 25% iron and 75% zinc ii. DELTA phase - zinc-iron alloy containing approximately10% iron and 91% zinc iii. ZETA phase - zinc-iron alloy phase comprising approximately 6% iron and 94% zinc iv. ETA phase - a pure outermost zinc coating A metallic bond is formed between the steel and the protective zinc coating. The phase layers are illustrated in the figure below form in strata on aluminium-killed steel. Initial surface has a silvery shine Pure zinc ETA phase layer ZETA phase layer DELTA phase layer GAMMA phase layer Steel When ”silicon killed steel” is immersed in molten zinc the HDG coating morphology that is formed will change according to the amount of silicon and phosphorous within the steel. The phases Page 13 of 23

develop at almost simultaneous rates resulting in a crystalline rather than the layered structure, the following two micrographs illustrate the variations. Steel Chemistry, be it aluminium killed or silicon killed will affect the final coating thickness and the initial aesthetic appearance of the article. The following are examples of the micrographic morphology and surface aesthetic for aluminium killed steel and variation in silicon killed steel Aluminium Killed Steel Typical micrograph of a hot dip galvanized coating with “aluminium killed” carbon steel (Silicon < 0.03% and zinc temperature 450°C) [Magnification 150 x) Page 14 of 23

Silicon Killed Steel (Silicon and Phosphorus) Cross-section through zinc coating on silicon Dark and light grey areas including cellular killed steel > 0.03% to <0.15%, typically patterns are the result of steel chemistry Si = 0.06% Zinc coating thicknesses range between Silicon (Si) and Phosphorous (P) or Si and 150µm to 250µm P acting together Silicon Killed Steel (Preferred silicon and Phosphorus Specification Range) Preferred structure of hot dip galvanized coating Two examples of typical surface produced using “silicon killed” steel within the finishes obtained with varying Si% silicon range of 0.15% to 0.25% and P <0.02% content in steel Zinc temperature 450°C Coating thicknesses range from 120µm to 200µm. Silicon Killed Steel with high Phosphorus content With high Phosphorous (P) >0.03% Low Si <0.04%, but P >0.035% Pronounced surface defects with tendency to flake, particularly under impact loads, such as mechanical damage from poor handling procedures Page 15 of 23

Skimming is necessary bot during the galvanizing operation to avoid ash collecting on the surface of the material being galvanized. The skimming operation must be carried out with a smooth flowing action. Excessive agitation and the creation of ripples or waves will increase the formation of more ash while not providing an ash free zinc surface. The skimming operation should take place in one direction only. This should be towards the end of the bath where the ash receptacle is situated. Prior to the removal of the article, the zinc surface is skimmed to remove ash and other contaminates . 6.4 Zinc Residues 6.4.1 Ash When the receptacle is full, the ladle should be used to remove the ash, taking care to avoid contact with the zinc surface. In this way, the quantity of metallic zinc removed will be low. In the case of the automatic pipe operation and with flux blankets, skimming is limited to the exit surface of the bath where there is no flux. When an excessive amount of ash has accumulated on the surface, it is also necessary to remove it. During long shut down periods, ash is allowed to remain on the molten zinc surface as it can insulate the surface and prevent un-necessary heat loss. The retention of an oxide film on the zinc surface also retards the formation of further ash. 6.4.2 Dross The build-up of dross is dependent on the volume of work galvanized and the reactivity of material being processed. Dross levels must be monitored and a regular routine drossing cycle established to suit the specific operation. While it is important to remove dross, one must also guard against excessive drossing as such practice leads to zinc wastage. The dross level is determined by means of a steel probe, which is used to check the level every week. If the layer exceeds 150 mm, in any given week, the bath must be drossed. i. Dross Removal A perforated spoon or ‘grab’ is provided, it must be inspected to ensure that the perforations are not blocked. Blocked holes will prevent entrained zinc from draining out of the spoon on withdrawal. Special care must be taken to ensure that the corners have been adequately cleaned. All dross removed must be weighed. New zinc is then added with the mass recorded and the zinc level increased to the standard position. Page 16 of 23

7. Water Quench, Passivating or Air-cooling This process douses the hot product in a low concentration chromate water-based quench. The articles quenched can be safely handled immediately after hot dip galvanizing. The quench subdues the formation of the zinc/iron phase layers which continue to develop above 300oC. The chromate passivation layer provides transitory protection of the newly formed hot dip galvanized coating from immediate reaction with the atmosphere. Rather it allows for an extended period in which the reaction between the zinc and the CO2 in the atmosphere are able to form the zinc carbonate layer (ZnCO3) or patina. The dried passivation-film is soluble in water and will be depleted within three to four months of field service. Hot dipped galvanized articles to be painted after the HDG process should be quenched in pure water or alternatively air-cooled, but should not be passivated. Page 17 of 23

8 De-Jigging, Fettling & Cleaning 8.1 De-Jigging De-jigging is the removal of hot dip galvanized articles and the slinging materials from the flight bar. Care should be exercised when de-jigging not to damage the product that has been now completely processed. Inspection at this point in the process should be conducted in accordance with the standard’s acceptance inspection criteria. In de-jigging each item is handled allowing an excellent opportunity to inspect each article in detail. 8.2 Fettling and Cleaning 8.2.1 Fettling Fettling describes the process of removing excess droplets of solidified zinc from the galvanized article after it has been de-jigged. Care must be taken to avoid over fettling and thereby removing significant quantities of the zinc coating. The amount of fettling and cleaning (removal of excess zinc) should be minimal. It should however be an operational objective to totally eliminate fettling. The fettling operator is using a gas flame to re-melt the excess zinc and a hand scraper to remove droplets of the resultant molten excess zinc. Page 18 of 23

Here the fettling operator is using a file to remove excess zinc. This is the non-preferred method of fettling. The fettling operator, if untrained could easily remove the whole zinc coating and expose the underlying steel to corrosion 8.2.2 Cleaning Cleaning is often required in order to remove entrained ash deposits resulting from inadequate skimming while withdrawing from the molten zinc. Ash deposits also tend to be trapped in crevices or internal surfaces in the case of complicated items and are normally difficult to prevent at the zinc bath. For this reason cleaning is unavoidable. The process should be to remove the ash without damaging or removing the actual galvanized coating. 8.2.3 Stacking Newly hot dip galvanized product must be handled and stacked correctly. The following diagram illustrates stacking in order to prevent “wet storage stains”. Wet storage stains arise from two galvanized surfaces being piled together and water (moisture) being allowed to enter a small space, crevice, between the surfaces. While avoiding wet storage staining is the key purpose of passivating HDG articles, the correct stacking of the articles is critical in avoiding this post galvanizing surface condition. Page 19 of 23

8 Inspection, Packing & Despatch 8.1 Inspection It is important to appreciate that once the cause of white rust is eliminated, further formation ceases, thus, if plates are unpacked, allowing free air circulation, the desirable stable surface film consisting mainly of basic zinc carbonate, will rapidly form. Excessive deposits of white rust should be removed preferably with a bristle brush or by chemical treatment. The use of a wire brush will tend to remove any stable surface film that may have already formed. Despite vigorous cleaning and removal of white rust deposits, temporary surface staining and discoloration of the coating usually remains. As the coating weathers, the discoloration disappears and the overall zinc surface assumes the typical uniform grey appearance. The presence of white rust is not necessarily a reason for rejection. Any white rust affected area should be evaluated to ensure that the hdg coating thickness conforms to the minimum thickness as stipulated in the specification. When coating thickness equals or exceeds the specified minimum mean coating thickness it is acceptable, subject to aesthetic requirements that may be important in specific cases. A magnetic flux instrument is typically used to determine the hot dip galvanized coating thickness across a range of 0 to 1500m. These instruments use magnetic flux to measure the coating thickness of any non-magnetic coating on a magnetic base material. The instrument is routinely calibrated to measure coating thickness to within a 5% range of accuracy. Page 20 of 23

Example of a yard with limited space, but well controlled Example of a large yard area with adequate space where controls are easier to implement and maintain. 9. Repair Procedures, Stripping & Re-galvanizing 9.1 Repairs (Surface renovation) Uncoated surface defects which may be renovated are defined as being within 0.5% of the total surface area of a HDG article with no single uncoated area exceeding 10cm² unless agreed to by the client. The HDGASA subscribes to two proven methods of repairing uncoated surface defects. The first is by means of zinc metal thermal spray. Typically this process is carried out at the galvanizing facility. However it is possible to transport the required equipment to site should the need arise. The second means of renovation is by the application of a two-part zinc flake infused epoxy. The HDGASA has formulated such a product, registered as “Galvpatch®”. Galvpatch® is available in a two part squish pack comprising a two-part zinc dust infused epoxy, which when mixed forms a dark grey gelatinous solution applied to any single uncoated areas of ≤ 10cm2. The SANS121:2011 (ISO1461:2009) standard requirements for renovation of such uncoated surfaces stipulates that such a coating have a minimum dry film thickness of 100m. Should renovation be needed for articles to be a duplex coated then such renovation applied to match the thickness of surrounding HDG coating thickness. Page 21 of 23

Notwithstanding the method used for renovation preparation and cleanliness of the area to be repaired must be free of contaminants and products of corrosion. The repair will be ineffective if the surface is not clean. Zinc thermal spray Galvpatch® consists of a “squish pack” containing a two-part epoxy into which metallic zinc dust is introduced to form a gelatinous mixture. The infused metallic zinc dust seeks to provide the repair material with some level of cathodic protection. When mixed Galvpatch® must be applied to the identified areas of the article’s surface within 30 minutes, by which time the epoxy will cure and harden. Galvpatch® used for site repairs Page 22 of 23

9.2 Stripping and Re-galvanizing Should the galvanized product be totally rejected, usually due to poor process controls as well as deviations from standard operating procedures, the zinc coating must be removed by “stripping” in Hydrochloric acid (HCl). Hydrochloric acid, with a pH of < 1, will attack the zinc coating and totally remove it. When zinc is immersed in hydrochloric acid (separate stripping bath) the zinc coating will be removed. Once the product has been stripped of all the zinc, it is returned to the main process operation. Should this take place immediately after stripping, within 3 to 4 minutes, it may be possible to skip the degreaser and proceed direct to the acid pickling bath. Such the product be delayed for an extended period before re-galvanizing, it is advisable that it be returned to the start of the operation. In re-processing the “stripped” product exactly the same rules and requirements will be enforced as if the product was being processed for the first time. Reject product, stripping and re-galvanizing is a wasteful and costly and expensive. Stripping zinc off of used jigged equipment is normal good plant practice. It is considered good galvanizing practice to install a separate stripping bath where the hydrochloric acid stripping solution does not form part of the HDG processing line. By using a separate stripping bath iron content is limited while at the same time zinc chloride (ZnCl2) that can be used for the manufacture of flux are created. Page 23 of 23