DIS-TRAN Steel Blog

DISCOLORATION: THE MARKS OF SUPERIOR QUALITY

Posted by DIS-TRAN Steel on Jun 15, 2016 9:30:00 AM

For hundreds of years steel has served as the physical backbone of civilization. Landmark structures all over the world including Paris’s famed Eiffel Tower, San Francisco's stunning Golden Gate Bridge, and Dubai’s towering Burj Khalifa (currently the tallest building in the world), all count steel as a fundamental material used in their construction.

Prized for its versatility and strength, design professionals rely on the indispensable alloy to bring creative compositions to life. But even seasoned builders are sometimes perplexed by a discoloration phenomenon that occurs in steel after workers galvanize it. The surprising fact is this -- the very same chemical properties that give steel its renowned durability also yields its unaesthetic blemishes.

Although seemingly unbreakable, steel has an Achilles’ heel in its susceptibility to corrosion. Harsh elements can weaken the alloy, and strip it of its strength. Builders coat steel to protect it from corrosive conditions, but often mistake normal discoloration for deterioration. While rust and other decay must be safeguarded against, there’s nothing to fear in the dark blotches and spotting that appear atop of steel surfaces. In fact, they should be welcomed as a positive sign that, chemically, everything is proceeding according to plan.  Check our “A Two-Part Recipe for Understanding Galvanized Coating Appearances.”

Galvanized steel structures for Utility IndustryDIS-TRAN Steel produces premium substation and transmission steel structures designed to be durable and environmentally-friendly. The superior chemistry of DIS-TRAN products lends itself to inherent discoloration, a mark of top-of-the-line quality. At the molecular level:

“The coloration variations on the steel are due to variances in the steel chemistry, primarily the silicon content of the steel. Hot dip galvanizing involves a chemical reaction between the steel atoms and the zinc atoms during the dipping process. The base steel chemistry sets the course for the final color and appearance of the coating.”  – PAT SMITH, DIS-TRAN Steel.

Your steel fabricator can offer the use of silicon controlled steel, while it is not easy to source silicon controlled steel in standard shapes, it can easily be sourced (at additional cost) for tapered tubular structures.

Silicon – naturally occurring element commonly found in steel; silicon is particularly reactive in molten zinc metal

Silicon-killed steel – steel treated with silicon as an oxidizing agent in order to reduce the oxygen content to such a level that no reaction occurs between carbon and oxygen during solidification. 
(as referenced https://www.galvanizeit.org/inspection-course/course/glossary#s)

To minimize these inherent variations, other methods to help mitigate the differences include light sweep blasting after galvanizing to even out the zinc patina oxidations. Or, chemical dulling is another method employed to provide a more uniform final zinc patina. Costs, climate, and manpower are all factors to consider when deciding which of these optional cosmetic measures works best for a specific construction project.

While it may be considered unsightly, discoloration is a natural and normal oxidation process that occurs through the galvanized steel process due to the chemical compounds found within the steel. DIS-TRAN’s first-class products are inherently prone to these color variations that serve as proof of superior quality. The topical imperfections are purely superficial, and the experts at DIS-TRAN have scores of knowledge to help reduce their visibility. If the appearance of these blemishes are of concern to your project, our professionals are happy to help you find an aesthetically pleasing solution. Give us a call today!

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Tags: steel structures, galvanized steel

Proper Draining and Venting Provisions for Steel Structures

Posted by Brooke Barone on Aug 7, 2014 2:33:00 PM

Something that might be viewed as a small, insignificant venting hole on a 10,000 pound steel structure, if not well thought out, could really have an adverse effect on production.

These mistakes, big or small, can delay or even put a halt to jobs. It’s key that all along the process, from engineering to detailing and quality control, there are people in place who know what to look for. Once the structure gets delivered to the galvanizer it can become difficult and more costly to make modifications because plates might already be cut, or everything might be welded up.

When creating fabrication drawings for galvanized structures, it’s important, as well as valuable, to know proper draining and venting provisions for these steel structures. If adequate venting and draining holes are not provided, the structures can run into many problems.

5 Negative Effects:

1. Air pockets can form, causing structures to rust out from the inside

2. Excess galvanizing buildup

3. Lead to longer fabrication times

4. Welded plate can blow out, causing safety concerns

5. Poor coating

Not having adequate venting and draining holes can really have an intangible effect: it’s hard to put a dollar amount on what happens when a structure either doesn’t have proper venting, or one of the five stated above occurs. It’s usually not too hard to correct if it’s caught up front, but the further it gets in the process, and closer to the delivery date, is when the scrambling might start. All the man hours it takes to call the engineer on record to approve revisions, or contact customers, plant personnel, the galvanizer, etc. can really put a stop to production, causing low production numbers and possibly delayed shipping. (But working with a trusted steel fabricator, can help to avoid these issues.)

excess galvanizing buildup

Some standard shape structures, such as square and rectangular tube columns and beams, are hollow, so provisions need to be made in order to allow galvanizing to easily flow and coat the inside portion of the structure. Sometimes fabricators will provide a small bar with a removable cover plate, attached with two (2) small stainless steel self-drilling screws. However, if the customer doesn’t feel this is sufficient enough, then the next suggestion could be to use a thicker bar with drill and tap holes, and two (2) A307-TAP bolts.  Some might suggest the use of expanded metal, but excessive build up can take place, which is unsightly and also impairs vision into the tube, hindering the Quality Control Department from being able to adequately determine if interior galvanizing coating is sufficient.

Other standard shape structures like channels, wide flanges and angles, are solid, with just the outside receiving coating. Some issues that can arise with this are air pockets and excessive galvanizing buildup. For these shapes, you need to watch where stiffeners, connection plates and brackets are welded that could form large pockets of air as the section is dipped into the kettle. Tapered tubular structures are also hollow like square and rectangle tubes.

As a designer, you are always trying to find the balance of putting enough holes for galvanizing while not putting too many to affect the structural integrity of the steel member. For example, if dealing with corners in a square and rectangular tube, slots or holes can be provided near these corners to prevent air pockets from forming, which can decrease the amount of galvanizing coating in the area.

The more you understand how the member is lifted and dipped in and out of the galvanizing kettle, the better you can locate the venting and draining provisions.

For more information about galvanizing and how it works, click here to read past articles.

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Tags: standard shape steel structures, galvanized steel, steel fabricator, galvanized structural steel, rectangular steel tube, steel square tube

Why Galvanized Structural Steel Craves Proper Venting and Draining

Posted by Brooke Barone on Oct 23, 2013 3:39:00 PM

Something that might be viewed as a small, insignificant venting hole on a 10,000 pound structure, if not well thought out, could really have an adverse effect on production.

We all make mistakes every now and then; no matter if you’re on the engineer side, or project coordinator, quality control or detailing side, mistakes happen. But these mistakes, big or small, can delay or put a halt to jobs. I know it’s easy to sometimes overlook something when we’ve done it so many times to where we could practically do it in our sleep.  But nonetheless, you have to make sure to keep an eye out and to catch mistakes before it gets too far down the production line.

When creating fabrication drawings for galvanized structures, it’s important, as well as valuable, to know proper draining and venting provisions for these steel structures. If adequate venting and draining holes are not provided, these structures can run into many problems.

5 Negative Effects:

1. Air pockets can form, causing structures to rust out from the inside

2. Excess galvanizing buildup

3. Lead to longer fabrication times

4. Welded plate can blow out, causing safety concerns

5. Poor coating

It’s key that along the process, there are people in place who know what to look for or have an eye for knowing what will work when it goes to the galvanizer. But if it passes through the line of engineering, detailing, quality control and then is delivered to the galvanizer, it might be harder and more costly to make modifications. Plates might already be cut or everything might already be welded up, making it more difficult to modify.

Not having adequate venting and draining holes can really have an intangible effect. It’s hard to put a dollar amount on what happens when a structure either doesn’t have proper venting, or one of the five stated above occurs. It’s usually not too hard to correct if it’s caught up front, but the further it gets in the process and closer to delivery dates, is when you might start scrambling. All the man hours it takes to call the engineer on record to approve revisions, or contact customers, plant personnel, the galvanizer, etc. can really put a stop to production, causing low production numbers and possibly delayed shipping. But working with a trusted steel fabricator, can help to avoid these issues.

excess galvanizing buildup

Some standard shape structures, such as square and rectangular tube columns and beams, are hollow, so provisions need to be made in order to allow galvanizing to easily flow and coat the inside portion of the structure. Other standard shape structures, like channels, wide flanges and angles, are solid so just the outside receives coating, which means air pockets and excessive galvanizing buildup can form. For these shapes, you need to watch where stiffeners, connection plates and brackets are welded that could form large pockets of air as the section is dipped into the kettle. Tapered tubular structures are the same as square and rectangle tubes, in the sense of being hollow.

For standard shape and tapered tubular structures, using removable cover plates on the ends of beams is a good option instead of welding solid plates to the ends. This allows for faster flow through the member and more adequate galvanizing.

Now, also to keep in mind, ensuring proper venting doesn’t mean place a bunch of holes all over the structure, but rather strategically supply the venting and drainage provisions. For example, if dealing with corners in a square and rectangular tube, slots or holes can be provided near these corners to prevent air pockets from forming, which can decrease the amount of galvanizing coating in the area.

The more you understand how the member is lifted and dipped in and out of the galvanizing kettle, the better you can locate the venting and draining provisions. As a designer, you are always trying to find the balance of putting enough holes for galvanizing while not putting too many to affect the structural integrity of the steel member.

 

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Tags: standard shape steel structures, galvanized steel, steel fabricator, galvanized structural steel, rectangular steel tube, steel square tube

The Sustainable Truth About Hot-Dip Galvanizing

Posted by Brooke Barone on Jul 25, 2013 2:54:00 PM

Over the past couple of decades, environmental awareness has been on the rise as more people are paying attention to how they can help preserve natural resources and lighten their carbon footprint. In the energy sector, this has been a controversial topic for many years. Refineries have been shut down, as well as nuclear plants and other industrial facilities due to greenhouse emissions and other environmental impacts.

More recently, concerns have been raised about whether or not hot-dip galvanizing is sustainable. Just to refresh your memory, hot-dip galvanizing is the process of coating fabricated steel by immersing it in to a bath of molten zinc that metallurgically bonds the zinc to the steel.  This practice has been around for over 150 years, and provides maintenance-free corrosion protection for decades. Also, galvanized steel used in public construction is an efficient use of tax dollars, due to the no maintenance for decades.

There are three fundamental steps in hot-dip galvanizing: surface preparation, galvanizing and inspection. During step one, surface preparation, the steel goes through three cleaning steps; degreasing, pickling and fluxing. It is pertinent that the steel surface is clean because zinc will not react. During the second step, galvanizing, the steel is dipped into a molten bath at 840 F, that is made up of 99 percent zinc. In the final step, the steel can either be visually inspected to find areas that did not react or a magnetic thickness gauge can be used to verify if coating thickness meets requirements.

galvanizing kettle

Sustainability

Sustainable Development (SD), according to the American Galvanizers Association (AGA), is the social, economic and environmental commitment to growth and development that meets the needs of the present without compromising the ability of future generations to meet their needs. The two most well-known and accepted ways for measuring sustainability are the combination of life-cycle inventory (LCI) and life-cycle assessment (LCA), and the US Green Building Council’s Leadership in Energy and Environmental Design (LEED).  

galvanized steel

The two primary elements in hot-dip galvanized steel are zinc and steel, which both have high recycling rates. The recycled content is determined by weight and then the recycled fraction is multiplied by the cost of the assembly to determine recycle content value. Hot-dip galvanized steel becomes one product when the zinc metallurgically reacts with the iron, becoming more than 70 percent combined recycled content, which definitely meets the requirements of Credits 4.1 and 4.2 of the Materials & Resources Credit 4: Recycled Content category.

recycled steel(a)International Zinc Association (IZA), Zinc Recycling, 2004. (b)Steel Recycling Institte, Steel Takes LEED with Recycled Content, March 2009

To further explain, let’s break down what zinc and steel actually are. Zinc is the 27th most abundant element in the Earth’s crust and exists naturally in water, air and soil. Annually, about 30 percent of the world’s zinc supply comes from recycled sources, and about 80 percent that can be recycled is reclaimed. Zinc is also essential for humans, and aids in kidney function, breathing, digestion, diabetes control and much more. Zinc can also be found in a number of products such as cosmetics, tires and in treatments like sunscreen, diaper rash, burns and more. But also to make note, an abundant amount of zinc to humans can be very harmful.

Steel is the most recycled material in the world, with 70 percent made from recycled material. It has also been vital in construction since the industrial revolution took place back in the early 1800s. But, if steel is left unprotected, it will fall victim to corrosion.

Waste Created?

LCI also examines how much solid waste is created throughout melting the material, casting into pieces and then fabricating the steel. The figure below, provided by AGA, shows just how little of solid waste is created. 

steel characteristics

Hot-dip galvanizing isn’t something new. It’s been around for centuries, and has been proven to protect steel from corrosion, while having minimal environmental, economic or social impacts. 

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Tags: galvanize, galvanizing, hot-dip galvanizing, galvanized steel, American Galvanizers Association, recycled steel

8 Most Common On-Site Concerns With Galvanized Steel

Posted by Brooke Barone on May 16, 2013 10:38:00 AM

When steel is delivered on-site the first thing that is noticed is the coating appearance. Upon further inspection, if discolored or lumpy areas are noticed, the most common concern is if it’s detrimental to the life span of the coating. But in many circumstances, the look tends to be more serious than the actual effects. 

Galvanized Coating

Here’s a list of 8 of the most common on-site concerns with galvanized steel, and why it occurs. 

1. Bare Spots- Smaller flaws have little effect on the service life of the coating, and can be somewhat self-healing. Some spots may require repair using such methods indicated by ASTM A 780, which includes painting with paints containing zinc, repairing with zinc-based alloys (hot sticking) or by using sprayed zinc (metalizing). But, uncoated, unrepairable spots can be grounds for rejection. Some causes of bare spots can be because of inadequate surface preparation, welding slag, rolling defects, sand embedded in castings or oxidized steel.

2. General Roughness-   This is usually due to excessive growth or unevenness of the alloy layers, which can be attributed to the steel’s chemical composition or original surface condition. Heavy coatings are usually rougher than lighter coatings because irregularity of alloy layers tends to increase with thickness. In most cases, a rough coating does not negatively affect the lifespan, as long as adhesion is good. But, there are always exceptions to the rules. For particular pieces where one surface mates with another, rough coatings can be detrimental.

3. Dross Protrusions- Dross is the zinc-iron alloy that settles to the bottom of the kettle. It produces surface protrusions when the dross layer becomes agitated from the dross inclusions. Dross protrusions tend to have little effect on the surface life since the corrosion rate is similar to zinc. However, extensive dross inclusions can be grounds for rejection because they tend to make the surface more susceptible to mechanical damage.

4. Lumpiness and Runs- A lumpy coating results when the withdrawal is too fast or when the bath temperature is too low, not allowing molten zinc to drain back into the bath. Delayed drainage from bolt holes, folds, seams or other pockets where zinc collects is a consequence of the design. When products come in direct contact with others while being withdrawn from the kettle can also cause a lumpy coating appearance. Although it’s not detrimental to the life span, some cases require a smooth finish.

5. Flux Inclusions- Flux inclusions occur when a layer of zinc-ammonium chloride floats on the top of the molten zinc. When the steel is submerged in the bath, the flux pushes to the side when the steel is pulled back out. Flux inclusions can be caused by several different scenarios, such as a stale kettle flux where it tends to adhere to the steel instead of clearly separating from the surface as the steel is dipped. If the underlying coating is sound, then flux deposits are not reasons for rejection.

6. Ash Inclusions- Similar to flux, ash may be picked up during the dipping of the steel. Zinc ash is the oxide film on the surface of the bath. Ash inclusions can occur when steel requires slow withdrawal from the bath, and has no effect on the service life. If improper skimming of the exit surface of the bath can lead to gross oxide lumps, and can reduce the effective thickness of the coating, which is not acceptable.

7. Matte Gray or Mottled Coating- Usually appears as a localized dull patch or wed-like area on a normal surface, and develops when there is a lack of free zinc layer on the coating surface during the cooling process. A matte gray coating is found mostly on steel with relatively high silicon or phosphorous content, since they are heavier sections that cool slower. Galvanizers generally don’t have prior knowledge of the steel’s chemical composition, and has no control over its occurrence.

8. Rust Stains- Surface rust stains are not cause for rejection if they are caused by seepage from joints and seams after galvanizing or steel being stored under or in contact with rusty steel. Rust stains like this are superficial and should not be confused with failure of the underlying coat.

Whenever a question arises on the advisability of galvanizing a certain weld material, fabrication or steel type, it is best to consult the galvanizer. Most of the issues can be addressed beforehand if all parties stay in contact throughout the process before the steel arrives at the galvanizing plant. Remember to keep these 8 concerns in mind next time you conduct a visual inspection to help avoid delaying projects. 

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Tags: galvanizing, galvanized steel, zinc, galvanized coating, zinc-iron alloy layers, steel coating, zinc coated steel, astm standards

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