The corrosion of steelwork in Australia costs billions of dollars in maintenance and replacement costs. The long term solution in most cases is to hot dip galvanize which gives a long lasting, durable and cost effective protective treatment. When you galvanize your product you are not only protecting it from the elements, but giving yourself peace of mind that the steelwork will outlast the project.
Check out the advantages of Galvanizing : Advantages of Galvanizing for more information
Architectural galvanizing generally means there is a higher priority placed on the aesthetic appearance after galvanizing over its ability to withstand corrosion. To achieve smoother, shinier coatings there needs to be comprehensive communication between the project manager and the galvanizer. Steel design, venting and steel composition all affect the end result significantly. The most significant aspect of achieving better looking finishes is the amount of time spent dressing the items after hot dipping. Because this is not standard practice, it is best to let the galvanizer know your requirements so they can address the issue before it leaves the yard.
Shape/design: If the item can be dipped at a steep angle and quickly, then the zinc can run quickly and evenly off the surface leaving you with a consistent coating. Complicated shapes with small holes will be slow dips that will run the risk of zinc and dross collecting on the items surface.
Venting: large holes placed in good locations will mean fast dips giving you a more aesthetically pleasing surface. An easy way to gauge hole size is to make each hole in hollow sections a diammeter of 0.15 X the longest side in RHS or of the diammeter in CHS.
Steel composition: Sandelin range steels will develop thicker, mottled, dull grey coatings due to the silicon acting like a catalyst to make the steel more reactive. Phosphorus can cause uneven growth rates of the coating resulting in inconsistent surfaces.
Weld voids: often returning welds around a cleat does not completely seal off the area. During the cleaning process, fluids get trapped in these voids and “squirt” out when immersed in the molten zinc. This leaves an un-galvanized area. Blasting RHS prior to galvanizing or being careful to return the weld completely can avoid major problems in this regard.
Galvanizing colour variation – there are many factors affecting the colour consistency of galvanizing. Cooling rates, steel compositions and steel surface profile can all affect this. Speak with your galvanizer about your specific project to get a better understanding of what to expect.
Weld slag: Even when welding with a mig system, there are small “glass” lines left on the weld that will not come off in the galvanizing process and will be seen as black lines on the weld when dipped. Cleaning the welds thoroughly will avoid this.
Wire marks: all steel is hung in the process with chains or wire. These leave marks where they touched the steel. They are repaired after galvanizing. To avoid them, lifting points will be needed – consult your galvanizer for more informtion.
Original Steel Surface condition: The galvanizing coat follows the surface profile of your steel. Old rusty steel will have a pitted surface that will show up when galvanized. Use clean, new steel and this will limit this.
Edge damage – if you have heavy laser cut plate, this will have very sharp edges and chips may occurr due to handling. Grinding the edges to reduce the sharpness will alleviate this.
For best results, the design has to be simple, vented well and made from the correct steel. Talk to the galvanizer before about what you want to achieve. For free advice, please contact Hartway by clicking the link Contact.
HDG stands for Hot Dip Galvanizing and the number (either 600 or 900) stands for the coating thickness measured in grams per square meter. You can convert grams per square meter to microns by dividing the g/m2 by 7 (eg 900g/m2 / 7 = +- 125microns).
The HDG600/900 comes from a standard called AS2312. These thicknesses are used as a scenario to illustrate the how a coating of this thickness would behave and how long the coating would last. Often these coating thicknesses get misunderstood as a set coating thickness for specifying for your steel. Generally the thickness of the galvanized coating is related to the thickness and composition of the steel. The galvanizer cannot control the thickness.
There is a standard called AS4680 that dictates what the minimum coating thicknesses should be. This is generally more practical in specifying the coating required for your steel.
The Australian Standard is AS4680 for hot dip batch galvanizing. There are many standards, but this is the one we commonly refer to as hot dip. For others see the page with all the standards available click here
You can do some of the following:
1. Ask your galvanizer to issue you with a declaration of compliance.
2. Engage a third party inspector or ask the Galvanizers Association of Australia contact for GAA
3. Use the Hartway online inspection tool click here
Galvanizing involves dipping a fabricated item into molten zinc at 450degrees. The zinc has to fill and drain from the article. More importantly, the molten zinc will super-heat any trapped moisture and this rapid, powerful expansion of liquid to gas has to be released from the item or it can lead to dangerous explosions. Please click here for the design page.
The cost is usually quoted as a rate per kilogram of galvanized steel weight. There are three parts to this – the galvanized steel weight, rate and any surcharges. see the costs page.
1. Galvanized steel weight is usually 5% heavier than the black steel weight of your structure eg you send us a 100kg beam, once galvanized it will weigh about 105kg. The 105kg is the weight we use.
2. Rate this varies and is related to the weight per running meter of the steel structure. Heavy sections can be charged at a lower rate as they have more weight to absorb the cost of dipping.
3. Surcharges are to pay for extra work required to dip the steel – this could be getting rid of paint, lacquer and zinc, or be related to handling like double end dipping, 3-dimensional or drilling holes.
The life of a galvanized article depends on various factors. The two most important are the thickness of the coating and the environment it is to be used in. The durability flyer will help with these predictions – go to durability flyer.
To help understand the range, if you have a steel pole with 85 microns of galvanizing on it, it will last between 5 and 10 years at Cottesloe beach and the same pole in Leonora will last upwards of 50 years. Remember – if you maintain something, it will always last longer – frequent wash downs with fresh water are a great way to increase the life span of your galvanizing.
Tha bath is 12.6m long x 1.4m wide x 2.7m deep in Canning Vale and 12.6m long x 1.4m wide and 3m deep at Naval Base. maximum dip sizes for both single and double end dips can be found by looking at the graphs on the design page. Click here for max size graphs .
Galvanizing and concrete is a hot topic, especially in areas close to the coast or with a high salt water table. Because you can’t see your steel reinforcing once it is all embedded in the concrete, it gets difficult to know whether your building is safe from spalling (concrete cracking away from the steel reinforcing due to corrosion of the steel) and if this will mean expensive repairs for you later down the track. Please have a read of this comprehensive paper developed in conjunction with the Galvanizers Association of Australia. All you wanted to know about galvanized reo bar.
Hot dip galvanizing thickness varies with the thickness of the steel and the steel composition. The coating varies from 45microns (320g/sq m) to above 300microns (about 2100g/sq m). Click to see a table of thicknesses.
It is interesting to note that inline products such as the galvanized hollow sections are usually about 30microns and electroplated products usuall do not exceed 20microns.
Painting over galvanizing is simple if you know what you are doing. There are two information brochures available for powder coating and general painting over galvanizing. Very basically, most painters will either acid etch or whip blast galvanized steel prior to galvanizing to remove the passivation coating of sodium bi-chromate. These systems are called duplex systems and will usually protect the steel for longer than the sum of the two coatings lives added together – gives you a synergistic effect that is often 1.5times. The new standard AS2312 has a section 7.5 that deals with how to paint galvanizing.
External (Male) threads or “green” surfaces: Usually the best way is to place a coating over the parts you do not want galvanized. Usual systems we see at Hartway are silicon and stop off paints like Jotun 605 or galvastop. If these are applied and allowed to dry before galvanizing, this usually stops the galvanizing from forming on that surface. The end result is an area or space on the article that is not galvanized.
If you are trying to protect a recently machined surface (flange faces, axles bearing surfaces), then the steel is often clean underneath the masking material. If a paint is used to mask the surface, it burns off during the process – this not true of galvastop. Clean surfaces underneath this will then usually galvanize. To avoid this, the best system to mask machined surfaces would be to use a nice thck layer of silicon or buy the purpose built galvastop.
The paint masking process is often more successful when masking beams etc that will need some sort of welding on site after (see picture below). The steel on these generally has some rust and so will not galvanize under the masking agent.
Internal (Female) thread protection: This can be done by putting plumbers tape on a bolt and then screwing this into the female thread. Using this method allows you to remove the bolt after galvanizing, without the use of tools and leaves less”mess” behind. If this can’t be done, then using silicon plugs or screwing a bolt into the thread without the plumber’s tape, are possible solutions.
We get a lot of enquiries about refurbishing boat trailers. There are three main considerations for you:
1. Cost: Redoing old trailers is usually cheaper than a new one, but some things to save you money: a). If you mix galvanized and painted materials, there will be a surcharge on each of these adding to the cost – keep all the steel coatings the same to save money. b). Inside hollow sections there is often a lot of rust that reacts adversely with the zinc and you end up with heaps of zinc stuck inside that adds to the weight and so costs you more – banging the frame about a bit to dislodge this will help. c). Blasted trailers will cost less. d) Hartway is able to give you a rate per meter of trailer if you do not know what the weight is.
2. The final product: The quality of the coating will be heaps better than your old one, but will never rival a brand new trailer – we are galvanizers and not genies! Getting rid of the internal rust, replacing old pitted surfaces and putting the required drain holes in will give you a good protective coating.
3. Preparing your trailer: a). Take off all tyres, winches, axles, springs, nuts, bolts, brackets, tow hitches, wiring and any aluminium tags – if you leave them on they will either get frozen in zinc or melt off into the bath. Speak to us if you need to drag the trailer to us and then use the space in our yard to work on it. b). Clean as much of the surface contaminants off it before it gets to the galvanizer – flakey rust, old paint jobs – note: don’t remove stickers – leave them on so we can grind them off(the invisible glue underneath them is our worst enemy and the sticker shows us where to grind).
Double dip is actually called a double end dip. This is for articles that are too large to fit in the bath in one go. One end needs to be dipped in and then the article turned around and the other end dipped in. This has implications for cost and lead time as it involves more work. Double end dipping introduces more heat into items and so distortion becomes a greater factor and good design is ciritcal.
This does not happen and is often confused with double end dipping. If we subject a galvanized item to the process twice, the first coating of zinc gets removed and then a new coating laid down.
There are some tricks to get thicker coatings – blasting the surface prior to galvanizing, careful consideration of the steel composisiton used, using thicker steel sections and various other dipping techniques that we hold close to our hearts.(pardon the pun!) Most hot dip galvanized coatings to AS4680 are above the required standard and so protect your steel more than you expect.
The short answer is no. The longer answer is why would you want to do this in the first place as the protective properties of stainless steel probably outweigh those of galvanizing. Most instances where this becomes an issue is when stainless steel is welded to a structure. The stainless sometimes gets a galvanized layer and sometimes doesn’t – it never looks very pretty after. If you can’t take it off then there is no functional problem with dipping the stainless steel.
Venting is a series of holes or snipes that allow free flow of fluids and ash during the galvanizing process. Without these holes the item often cannot be safely and successfully dipped. The hole positions and sizes vary according to the size and shape of the steel components. A general rule of thumb is that all hollow sections need holes at either end that are at least the equivalent of 25% of their cross-sectional area. If you can imagine that the zinc is like warm melted chocolate filling and flowing about the items, then it becomes clear you need big holes to let it all through. Click here for our design page.
Hot dip galvanizing is a process where we take steel items and clean them in acid and caustic solution and then dip them into a large bath full of molten zinc. The steel and zinc react together at 450celcius to produce a layer made from the alloying of iron and zinc. This layer has better corrosion properties than steel and is harder than the base steel. It is one of the most simple, comprehensive and cheap processes to protect steel and has been so for the last two centuries. Hot dip is different to electroplating. Hot dip is usually thicker, duller in colour, harder and has better protection against corrosion. Electroplating is thinner, smoother and has a shiny lustre.
The lead time for most galvanizers varies with the local work loads. These lead times vary from 3 days to as much as 10 days. Lead times are also affected by the condition of the steel. Things that slow us down are painted or galvanized steel, heavily oiled steels, large structures needing double end dipping, the quantity of steel to be dipped and poor paperwork (we end up looking for a needle in a haystack when you are hoping we will find a thimble) Always good to contact us and get a more accurate time frame.
Generally most baths run at around 450 celcius.
The size, quantity and placement of holes is ciritcal to getting a good coating. Please click on the link for the design page – Design.
This is the normative governing standard for hot dip galvanizing (static immersion) in Australia and New Zealand. Hartway is compliant to this standard. We can’t put a copy of the standard on our website due to copyright restrictions. Further information can be found by contacting us or by buying the standard – SAI Global Site for Standards.
This is an Australian standard that gives information on the corrosive zones in Australia and various coatings that are available and appropriate. It does not govern the galvanizing process as this is slave to the standard AS4680. Further information can be found by contacting Hartway or by buying the standard from SAI Global’s Website.
This is an Australian standard for the preparation (cleaning) of steel for coating. Galvanizing makes use of the part AS 1627.1 (removal of oil, paint and grease) and AS1627.5 (pickling of steel in acid to clean it). Hartway is compliant to these pre-clean procedures.
Interesting to note that we will always put our steel through a pickling process (AS1627.5) and so holding the blast on blasted items is not an issue.
Hartway will always put steel through the pickling process (AS 1627.5 using HCl acid) and so there is no requirement to hold the blast.
If steel has been blasted to minimise the problem of hydrogen Embrittlement of high tensile steels, then the blast will have to be held as the pickling process will not be used. Communication with Hartway is ciritical in this instance – contact Hartway.
Yes this is possible. Steels over 900MPa need to be relieved after the galvanizing process to remove any Hydrogen ions that may be trapped in the steel molecular structure. If this is not managed, then there may be the problem of hydrogen embrittlement, which makes the steel brittle and prone to brittle fracture. Contact Hartway for more infomation – Contact us.
No, the bath is a huge bath of molten zinc that would be very hard to move about safetly.
We have runs to most Perth metropolitan areas and to the South West. We do not have hiab trucks and so need to collect and deliver from workshops with loading facilities and hardstand. We can only carry normal loads – any over-size will need to be transported by a professional logistics company. Our dispatch teams can help with your enquiry and can be reached on these contacts.
As with all coatings, regular maintenence is the best way to enhance the lifespan. Regular fresh water wash-offs are recommended. This removes any airborn salts that have accumulated on the surface. Boat trailers are best washed down at the boat ramp to prevent the sea water drying off while you drive home and leaving concentrated salt residues that are highly corrosive.
Painted galvanizing usually last much longer that either of the two systems combined individually. these duplex systems are very resistant to highly corrosive environments.
We are happy to do any size job. We do have a minimum charge in place and this is usually around the $50 mark. For more accurate and current information it is always good to contact us – click here for contacts.
Our normal operational hours for the dispatch office are 7am to 430pm Monday to Friday.
Distortion is due to two main reasons :
1. Different specific heats:
- Different thickness steel: Design and fabricate sections of uniform steel thickness. Different thickness steels expand and contract at different rates and so move relative to each other.
- Speed of dipping : Ensure that venting and draining holes are adequate. This will allow the item to be immersed and withdrawn from the molten zinc as quickly as possible.
2. Yield strength change :
- Symmetrical designs: Use symmetrical designs where possible, and avoid asymmetrical designs where cleats or plates are welded to one side only of a beam or RHS section.
- Plate: Avoid designs which require fabrications with a large surface area of thin plate to be double-dip galvanized.
Balanced Welding : During fabrication use balanced or staggered welding techniques to avoid uneven locked-in stresses.
Uniform cutting process : If cutting a plate to size, ensure all sides are cut using the same technique. Guillotine is the preferred cutting technique.
Yield strength change – Ensure that the structural design of the item is sufficient to support its own weight at 50% of the steel specified yield strength. Consider temporary bracing if potential to yield exists.
Often people ask about bolt holes and axles and how the internal or external diammeters will change with galvanizing. Most galvanizing will add between 70 and 200 microns to a surface. A micron is one thousanth of a mm ( 1 micron = 0.001mm ). This means that the diammeter on ONE surface will change by between 0.07mm and 0.2mm.
In the case of a bolt hole the diammeter will reduce by twice this as the galv coats both sides of the hole – bolt hole diammeter will DECREASE by between 0.14mm and 0.4mm. In the case of an axle the external diammeter will INCREASE by the same amount.
Thread sizes are not as simple and will generally change by twice the thickness of the coating on EACH side for coarse metric thread. eg 100microns of zinc will change the diammeter of the thread by 0.4mm, 150microns of zinc will change the thread diammeter by 0.6mm. This information is offered to help and it always best to approach a professional bolt maker if you are dealing with low tolerances as they will have more accurate data.
When two steel sections overlap each other and they are fully seal welded, there is a small space between them that needs to be able to vent during dipping in the bath. There are 3 things to think about when looking at this:
1. Number of holes – you need a minimum of one 6mm hole per 100cm2 of overlap.
2. Location of holes – when put through th pre-treatment process the fluids go in between the surfaces and will collect in corners, so you need to allow a hole in a corner of the overlap to let the last bits to drain out.
3. Prevention of weeping after galvanizing: Most weeping ocurrs because there is a salt formed in the pre-treatment process from the caustic – if you can blast the pieces before welding them together, this avoids the caustic process and so limits the chance of weeping.
Galvanizing is an alloying reaction that involves zinc molecules diffusing into the steel surface. Zinc is silver and steel is a dark grey. When the two mix a resultant colour is produced. The extent of the alloying is dependent on steel thickness and steel composition.
1. Steel thickness: thicker steel holds heat for longer and so allows the alloying reaction to continue and the silver zinc on the surface continues to diffuse into the steel giving it a duller grey colour. Thin sections, however, cool much faster and so the diffusion stops and leaves the silver layer of pure zinc on the surface.
2. Steel composition: Silicon is present in most steels. If it is present in the range of 0.04% to 0.14% this is called a sandelin range steel. Sandelin steels are very reactive and so the diffusion occurs faster and for longer – this gives you a thick and dull coating. Remember, thicker coatings usually mean longer lasting protection.
Eventually the surface off the galvanizing reacts with the atmosphere to form a dull grey zinc carbonate layer, called a patina. This is hard, UV resistant and not soluble in water and acts like a protective layer, slowing down any interaction with the atmosphere. Slow reaction with the atmosphere means a longer life!