Galvanized And Stainless Steel

Stainless steel is the most common metal, and galvanized steel is no less common 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.

Summary of core differences

• Corrosion resistance mechanism: galvanized steel relies on sacrificial protection of the zinc layer, while stainless steel relies on a self-repairing oxide film.
• Applicable environment: galvanized steel is suitable for general industrial environments, while stainless steel is suitable for scenes with high corrosion or strict hygiene requirements.
• Cost-effectiveness: galvanized steel has low initial cost, while stainless steel has a low long-term maintenance cost and a longer life.
• Aesthetics and processing: stainless steel has better appearance and stronger processing adaptability.

Physical properties

Physical properties of Stainless Steel

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

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

SS steel & GI steel characteristics

Galvanized steel is coated with zinc to protect it from rust, while stainless steel is an alloy made with at least 10% chromium; the two have different chemical compositions, but both have the purpose of corrosion prevention.

1. Stainless steel is the king of rust prevention and has excellent corrosion resistance, even in the atmosphere, water, acid, alkali, salt, and other media.
2. The surface is smooth, the color is bright, and it is easy to process. It can be polished, brushed, and mirrored to enhance the texture.
3. Unlike galvanized steel, its good weldability ensures the corrosion resistance of the welded joint and has excellent welding performance.
4. Its safety and hygiene level is higher than that of galvanized steel, and it is widely used in hospitals, biochemical experiments, surgical instruments, and food industries.
5. It has both strength and toughness, and its strength after alloying is higher than that of some galvanized steel. The price is more expensive than galvanized steel.
6. It can be completely recycled and reused, and it is more environmentally friendly. High temperature and low temperature do not affect its good performance.

Galvanized Steel features

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. 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.

How to tell galvanized steel from stainless?

Appearance and color

• Galvanized steel: Silvery white or gray, may appear slightly rough when the zinc layer is thick. There may be zinc flowers on the surface (typical characteristics of hot-dip galvanized steel), and it is not as smooth as stainless steel.
• Stainless steel: The surface is smooth and bright, usually silvery white or with a metallic luster. There are no obvious flaws or accumulation marks, and the texture can be further improved by polishing and other treatments.

Magnetic test

• Galvanized steel: It is magnetic and can be attracted by magnets. Compared with stainless steel, it has stronger magnetism.
• Stainless steel: It varies by type. 304 and 316 austenitic stainless steels are non-magnetic or weakly magnetic, while martensitic or ferritic stainless steels may be magnetic.

Corrosion resistance test

• Galvanized steel: In a humid or corrosive environment, the zinc layer may gradually corrode and produce white or gray corrosion products.
• Stainless steel: The dense chromium oxide film on the surface makes it significantly better than galvanized steel in corrosion resistance. In the same environment, the corrosion rate of stainless steel is much lower than that of galvanized steel.

Chemical reagent test

• Galvanized steel: The zinc layer reacts with certain chemical reagents (such as dilute hydrochloric acid) to produce bubbles (hydrogen) and gradually dissolve the zinc layer.
• Stainless steel: It is resistant to corrosion to most common chemical reagents and does not produce obvious chemical reactions or bubbles.

Hardness and weight test (auxiliary method)

• Galvanized steel: The substrate is ordinary steel, and the hardness depends on the steel itself. At the same size, the weight is similar to stainless steel. When accurately measured, the zinc layer will slightly increase the weight.
• Stainless steel: Some types of stainless steel (such as martensitic stainless steel) have higher hardness. The density is slightly higher than ordinary steel.

Professional testing

• Spectral analysis: Use a spectrometer to detect the composition of the material. Galvanized steel mainly contains iron and zinc, while stainless steel contains alloy elements such as iron, chromium, and nickel.
• Metallographic microscope: Observe the microstructure of the material. The surface of galvanized steel is covered with a zinc layer, while stainless steel presents a uniform alloy structure.

Can stainless steel be galvanized?

Stainless steel does not usually require galvanizing, but it can be galvanized in special circumstances. 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.

Can you use galvanized and stainless steel together?

Galvanized steel and stainless steel can be used together, but the following key points should be noted to avoid galvanic corrosion.
1. Wet/salt spray environment, underwater/chemical environment.
2. Electrical isolation is recommended for the connection method. Zinc blocks are added as sacrificial anodes when conductivity is required.
3. Check the contact area for white rust every year. The inspection cycle should be shortened to 6 months in coastal areas.

Typical applications include stainless steel bolts fixing galvanized steel beams (low risk indoors), galvanized guardrails and stainless steel handrails separated by insulating sleeves, and galvanized body panels and stainless steel exhaust systems are kept apart.

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.

FAQs

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.

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 steel 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 prevent galvanic corrosion between galvanized steel and stainless steel?

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

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.

Application

Application of galvanized steel

• Construction: used to make supporting beams and columns in steel structure buildings, low decorative materials for building facades, light steel keels for industrial and civil buildings, galvanized pipes for water supply and drainage, etc.
• Electricity: commonly used to make cables, bridges, power dry towers, substation equipment, transmission towers, communication base stations, etc. Its mechanical properties and corrosion resistance can ensure the long-term stable operation of the power system.
• Petrochemical: commonly used for transportation pipelines, storage tanks, chemical equipment, chemical reactors, heat exchangers and pipeline systems, steam reforming units, distillation towers, oil pipelines, etc., with high temperature resistance, corrosion resistance and other properties, which can ensure the safety and stability of petrochemical facilities.
• Agriculture: often used to make channels, drainage pipes, cattle pens, etc., with the advantages of corrosion resistance and high tensile strength, which can ensure the stability of agricultural production.

• Municipal engineering: commonly used to make street light poles, guardrails, bridges, road guardrails, etc., with weather resistance and corrosion resistance, which can ensure the long-term stable operation of municipal facilities.
• Industrial equipment: used for warehouse shelves, logistics platforms, equipment bases, conveyor belt brackets, etc., suitable for factory environments, load-bearing and rust-proof.

Applications of stainless steel

• Construction: used for structural components, roofs, handrails, building facades and decorative elements, urban sculptures, room decoration materials, etc.
• Chemical processing: stainless steel containers, heat exchangers, reactors and piping systems are common choices in chemical experiments and industrial production.
• Food processing: stainless steel kitchenware, pipes and tanks such as water heaters, washing tanks and drums of fully automatic washing machines are indispensable in food processing to ensure hygiene and safety.
• Medical equipment: surgical instruments and medical devices are usually made of stainless steel because of their corrosion resistance and easy cleaning characteristics.

• Automobile: manufacturing fuel tanks, automobile exhaust systems and structural parts. Each car’s exhaust system uses about 20-30kg of stainless steel, and the global annual demand is about 1 million tons.
• Energy: used for nuclear power equipment, thermal power equipment and solar equipment, aerospace equipment, such as turbine blades of power generation equipment, boiler pipes, nuclear reactor components, transformer housings of substations, switchgear, grounding systems, aircraft components, etc.
• Ocean: Ship equipment, seawater desalination systems, fishing gear, bridges and offshore platform structures such as key parts of ship structures, drainage systems and fuel tanks.
• Shipbuilding and papermaking: Stainless steel plays an important role in shipbuilding. In paper machines, stainless steel is used to ensure stable and efficient operation from the frame, roller to the transmission system.
• Daily life: 316L stainless steel is an ideal material for the inner and outer frames of glasses and smartphones. In addition, it is also used for kitchen cabinet panels and countertops, range hoods and stoves, sinks and faucets, bathroom cabinets and mirror frames, towel racks and storage racks, and table and chair frames.

Selection suggestions

If you need economy and low environmental corrosion, galvanized steel is preferred.
If you need high corrosion resistance, aesthetics, or long-term use, stainless steel is preferred.

Summary

Galvanized steel and stainless steel are two core anti-corrosion materials in modern industry, each with its own unique advantages. Galvanized steel has become the first choice in construction, infrastructure, and other fields due to its economy and reliable zinc layer protection; stainless steel, on the other hand, is irreplaceable in harsh environments such as the chemical industry and marine engineering due to its inherent corrosion resistance and high strength. When the two are used together, special attention should be paid to the risk of galvanic corrosion. Scientific means such as insulation, isolation, potential matching, or sacrificial anode can effectively extend the life of the structure.

In actual projects, it is recommended to comprehensively evaluate the material solution based on the environmental corrosion level, cost budget, and maintenance conditions. For high-demand scenarios, professional material engineers can be consulted for corrosion simulation and compatibility testing to ensure safety and reliability.

Wanzhi Steel provides a full range of galvanized and stainless steel products and technical guidance to provide the best anti-corrosion solution for your project!