Galvanized And Stainless Steel

Stainless steel is the most common metal, and galvanized steel is no less than it. So, as they are both metals, what are the differences in the performance of galvanized and stainless steel? Can ss be galvanized? Is it galvanized steel? Can it be put together with galvanized steel? Can they be welded together? How to prevent galvanic corrosion between the two? How to distinguish them in daily life, and what will happen when welding them? Which one has a longer lifespan, stainless steel or galvanized steel, and what are their practical applications? Read on and you will find the answers.

Is stainless steel compatible with galvanized?

Under atmospheric conditions of moderate to mild humidity, contact between a galvanized surface and a stainless steel surface is unlikely to cause substantial corrosion. However, if the surfaces are in the presence of salt water or saltwater air, it would be best to electrically isolate the two metals.

Can stainless steel be galvanized?

Since stainless steels from the 400 series do not contain nickel, they cannot be hot-dip galvanized. There are over 50 types of stainless steel, but as long as they contain some nickel in their chemistry (e.g. 300 series), they can be hot-dip galvanized.

Stainless steel products are not usually galvanized directly. Instead, the most common reason for this is that manufacturers need to weld stainless steel parts to pass galvanized steel before galvanizing them.

What is the difference between stainless steel and galvanized?

Galvanized steel is coated with zinc to protect it from rust, while stainless steel is an alloy made with at least 10% chromium for the same reason: to guard against rust and corrosion.

There are several types of stainless steel, each determined by the type and amount of additional materials, like chromium, as well as nickel, titanium, manganese, and/or molybdenum, present in the steel:

1. Austenitic stainless steel

2. Ferritic stainless steel

3. Long-wearing martensitic steel

4. Duplex stainless steel

5. Precipitation-hardening stainless steel

Galvanized Steel

1. Galvanized steel is water-resistant, but it does not hold up well under salt water.

2. Compared to stainless steel, it’s easier to work with and much less expensive.

3. For many construction applications, galvanized steel is a trusted, economical choice, as long as it won’t be in contact with salt water.

4. However, there is a downside to the welding process: the zinc coating will release toxic fumes that can cause flu-like symptoms and discomfort, so welders must be equipped with appropriate protective equipment.

5. Since welding removes zinc from the weld area, that area is left exposed and susceptible to corrosion.

Most of the time, it is best to galvanize the steel after welding is complete.

Stainless steel

1. Exceptionally strong and rust-resistant, stainless steel withstands contact with both fresh and saltwater—but not chlorinated water, which will cause the steel to degrade quickly.

2. It offers more corrosion resistance than galvanized steel, making it a great choice for marine and aerospace applications.

3. One major drawback is the cost: stainless steel can be about five times more expensive than galvanized steel.

4. It also requires highly skilled welders with exceptional patience and control.

5. Further, stainless steel can weld itself together if two pieces are in contact and the friction rubs through the coating, which could be a concern in certain applications.

Benefits & Drawbacks of Galvanized Steel VS. Stainless Steel
Benefits	Galvanized Steel	Stainless Steel
	1. Water-resistant	1. Exceptionally Strong
	2. Easier to work with	2. Rust-Resistant
	3. Less Expensive	3. Fresh and Salt Water-Resistant
	4. Economical Choice	4. Corrosion Resistant
Drawbacks	1. Does not hold up well under saltwater	1. Does not hold up well under chlorinated water
	2. Welding Process Zinc coating releases toxic fumes	2. Expensive
		3. Requires highly skilled welders
		4. Weld itself together if two pieces are in contact

Can you use galvanized and stainless steel together?

Galvanized steel in contact with stainless steel is not normally considered to be a serious corrosion risk, except possibly in severe (marine type) environments. In these situations, precautions such as insulating barriers are usually considered adequate to avoid bimetallic corrosion in most practical situations.

In the presence of an electrolyte, stainless steel and galvanized steel will undergo a chemical reaction, that will shorten the life of the Anode Metal, this chemical reaction is galvanic corrosion.

The table below is an example of these ‘metal-to-metal’ relationships.

ANODIC (Least Noble)

Magnesium

Zinc

Aluminium

Carbon steel or cast iron

Copper alloys (brass, bronze )

Lead

STAINLESS STEEL

Nickel alloys (Incoloy 825, Hastelloy B)

Titanium

Graphite

CATHODIC (Most Noble)

If the metals are dry, bimetallic (galvanic) corrosion cannot occur.

However, seawater or salt-laden humid air is a greater risk than exposure to rain or tap water. So in the marine environment, stainless steel can suffer from severe localized pitting.

What is electrochemical corrosion (bimetallic corrosion)？

It is Galvanic corrosion, also called bimetallic corrosion or dissimilar metal corrosion. It refers to two dissimilar metals, such as galvanized and stainless steel, the outer layer of galvanized steel comes into contact and is exposed to an electrolyte, such as water, one metal will corrode faster than when it is not in contact with the other.

So, it means three conditions must be met for galvanic corrosion to become a concern:

1. Multiple metals must be present with varying electrode potentials or nobility. The greater the difference, the greater the risk of galvanic corrosion.

2. These metals must be in electrical contact.

3. Exposure to an electrolyte — such as saltwater — must occur.

In the process, one metal — the anode — will corrode faster than it would alone while the other — the cathode — will corrode slower than it would alone.

How to prevent galvanic corrosion between galvanized steel and stainless steel?

Corrosion is a key issue when we select materials and design processes. Whilst stainless steel is highly resistant to many forms of corrosion, preventing the development of corrosion is essential for long-term safe use and cost reduction.

Much of minimizing galvanic corrosion risks is simply avoiding combinations of the three elements listed above.

 

However, for many industries — such as those processing chemicals or operating off-shore in salt-rich environments — this is easier said than done.

THE GALVANIC SERIES (ELECTRODE POTENTIAL) EXPLAINED

As highlighted in the image above, many stainless steel alloys rank toward the cathodic end of the scale.

This means they are less likely to suffer damage from galvanic corrosion. However, if used with highly anodic fasteners, structural elements, valves, or other components, the large difference in nobility can lead to rapid degradation of the other components.

Understanding Environmental Components Of Galvanic Corrosion

It is important to note that galvanic corrosion risks will also vary based on the electrolyte connecting both metals. For example, the risks of galvanic corrosion in very pure water are minimal. Yet, deploy the same metals in a marine or chloride-rich environment and you could see corrosion occur very rapidly.

The following chart offers examples of what galvanic corrosion risks to expect from common metal combinations.

Specific measures to reduce galvanic corrosion

1. Insulate the different materials with a coating of non-conductive material, grease, paint, treatment, or primer. Insulating the two materials that will be in contact provides the best protection.

2. Use buffers between dissimilar metals (e.g. pipe insulation tape, gaskets, fixture linings)

3. Choose suitable connectors or fasteners, and use fasteners made of materials compatible with galvanized and stainless steel, such as copper-nickel Choose suitable connectors or fasteners, and use fasteners made of materials compatible with galvanized and stainless steel, such as copper-nickel, brass, and other corrosion-resistant materials, bolts, nuts, etc.

What lasts longer, galvanized or stainless steel?

The two materials are manufactured differently. Galvanized steel is coated by dipping regular steel into molten zinc, hence the name “hot dip” galvanizing. Stainless steel is an alloy steel that is more corrosion-resistant than galvanized steel due to the addition of chromium and a different chemical composition.

The presence of chlorine and salt can actually cause type 304 stainless steel to degrade, so it’s not the best metal to use in swimming pools, wastewater treatment plants, or near the ocean. Type 316 stainless steel, on the other hand, has molybdenum added to it, which makes it resistant to salt and chlorides.

 

What happens if you galvanize stainless steel?

The electrical movement between the two metals causes the stainless steel to corrode at a slower rate than normal and the galvanized steel to corrode at a faster rate than normal.

Is stainless steel galvanized?

No, it is not. Galvanized steel is steel that features a zinc coating, which helps to create a barrier between the steel and the air and moisture, protecting it from rust. Stainless steel is steel that is mixed with at least 10% chromium to create an alloy that is corrosion-resistant, as well as bacteria-resistant.

Can stainless be welded to galvanized?

When welding galvanized steel (or steel coated with a zinc-rich coating) to stainless steel, it is essential to remove the zinc from the heated zone because it is possible to get zinc into the weld, which will cause liquid embrittlement and cracking along the zinc penetration line.

How to tell galvanized steel from stainless?

While both types of steel have a similar appearance, it can be difficult to tell them apart just by looking. However, there are several approaches to determining the two:

1. Touch:

Try to scratch the surface of the cable with a sharp object; stainless steel will have a smooth, shiny finish, whereas galvanized steel will be rougher to the touch.

2. Magnet:

Another way to determine it is to use a magnet. If it is made from galvanized steel, it will be attracted to the magnet. Stainless steel is non-magnetic and will not be affected by magnets.

3. Colour:

Most stainless metal will be silver, while galvanized steel will be dull gray.

4. Weight:

Stainless steel is heavier than galvanized, so if the cable feels unusually light, it could indicate it is galvanized.

Physical properties of Stainless Steel	Symbol	Value	Units
Thermal conductivity	k	25	W/M0C
Density	ρ	8000	Kg/m³
Specific heat	Cp	400	J/kg0C
Solidus temperature	Ts	1500	0C
Liquidus temperature	Tl	1525	0C
Latent heat of fusion	Hm	1.93*109	J/m³
Absorption coefficient	α	1*105	10-1
Staring temperature of Martensite	Ms	350	0C
Austenization temperature	TA	750	0C

 

Physical properties of Galvanized Steel	Symbol	Value	Units
Yield strength	Re	300	MPa
Density	ρ	7833	Kg/m³
Thermal Diffusivity	α	84.18*10-6	M2/s
Specific Heat	c	896	J/kgK
Thermal conductivity	k	65	W/m.K
Ultimate tensile strength	UTS	400	MPa
Young’s Modulus	E	210	GPa
Poisson’s Ratio	G	0.3	τ / γ
Weight heat	J	465	kgK

Is galvanized steel suitable for outdoor use?

Yes. Galvanized steel boasts impressive longevity, lasting over 20 years even in harsh outdoor conditions. It can shrug off heavy winds, hail, and even resist significant impacts without warping or breaking. This resilience makes it ideal for structures that need to withstand the toughest weather conditions.

Applications of Galvanized Steel vs. Stainless Steel

Typically, galvanized steel is a more economical choice because it is not only cheaper in material and labor but also has commendable strength and longevity.

However, galvanized steel is not suitable for all environments. For example, it does not work well in marine applications, in which case stainless steel becomes an indispensable material.

Therefore, the choice of galvanized steel or stainless steel depends on your application!

1. Hinges, washers, and fasteners such as nuts, bolts, screws, and nails are usually made of galvanized steel to withstand extreme weather conditions.

The use environment of these parts is not so demanding, so galvanized steel is preferred to save costs to the greatest extent.

2. In high-humidity environments such as automotive exhaust pipes, marine applications, and aerospace industries, stainless steel is usually the best choice.

Summary

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