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Understanding Stress Corrosion Cracking in Duplex Stainless Steel

Understanding Stress Corrosion Cracking in Duplex Stainless Steel

Duplex stainless steel has become more and more popular for its combination of strength and affordability. Not only can duplex stainless steel hold up reliably through trauma impact, but through corrosion as well.

To understand the corrosion resistance properties of duplex stainless steel, you must also understand the concept of stress corrosion cracking. Let’s discuss what it entails, and how it relates to duplex.  read more…

What are the Benefits of Duplex Stainless Steel?

What are the Benefits of Duplex Stainless Steel?

Duplex stainless steel, sometimes called S31803 or S32205 stainless steel, is an alloy which consists of both austenitic and ferritic stainless steels. The combination of these two stainless steel types creates an alloy with terrific versatility.

Not only are duplex stainless steels strong, but lightweight and affordable as well.  Though they’re not perfect, they do very arguably offer the most bang for their buck.

So what are the exact benefits of duplex stainless steel? Let’s discuss.  read more…

How Does Stainless Perform in Natural Disasters?

Those involved in project management know the importance of choosing the right materials for the job. It is necessary to pick materials that are equal to the demands of daily use. Additionally, increasing severity of natural disasters of a number of descriptions should be considered to ensure that your operations remain active and safe even in the face of severe weather events.  read more…

What is a dual-phase (Duplex) stainless?

Balancing costs against the qualities you need most is of vital concern during stainless steel fabrication. Picking the right alloy allows you to get the characteristics that are necessary for the job without breaking the bank. Dual-phase stainless steel, which more commonly known as duplex stainless steel, can satisfy many requirements economically.

What are the features of a dual-phase steel?

Duplex stainless steels have a two-phase microstructure. The microstructure is a mix of Austenitic and Ferritic stainless steel. This family of stainless steels is relatively new, having been first engineered in the 1970s. However, it quickly found wide use once it was discovered.

By keeping a lower Nickel content than Austenitic steels, Duplex achieves the balance between Austenitic and Ferritic structures.

Duplex steel takes good characteristics from both Austenitic and Ferritic which means it has a corrosion resistance comparable to that of Austenitic grades but has higher mechanical properties.  It also has a good weldability and does really well when it comes to toughness at low temperatures compared to ferritic steels. It is specifically very popular when it comes SCC (Stress Chloride Cracking) and Pitting corrosion.

Is dual-phase steel economical?

Two-phase stainless steels typically contain lower levels of nickel and molybdenum than austenitic steels. This makes it relatively economical especially during the times when Nickel price goes up.

S31803, commonly referred to as Duplex, for instance, is high in chromium but contains only around 4.5 to 6.5% Nickel. The higher strength allows reduced section thickness and therefore reduced weight in applications such as boats, pressure vessels, bridges etc. Overall, it reduces the cost of the project.

Corrosion resistance and Duplex stainless steel

PREN (Pitting resistance equivalent number) is a good measure of comparing corrosion resistance of various alloys. PREN formula is, PREN = %Cr + (3.3 x %Mo) + (16 x %N). Duplex has a PREN value of approx.. 35 which about 10 numbers more than Austenitic grade 316. Higher the PREN Number, better the corrosion resistance to pitting.

As indicated earlier, Duplex steels have a very good SCC (Stress Chloride Cracking). SCC occurs when there is a corrosive environment coupled with tensile stress.

At Great Plains Stainless Steel, we take great pride in our knowledge of stainless steel grades and alloys. Not sure what you need for your next project? We can help. Get in touch today to discuss your needs. We’ll identify the right materials and the right construction for you.

Can stainless steel rust?

Many people are surprised to learn that stainless steel is not impervious to rust. However, this is not universally true. In fact, different types of stainless can have different levels of rust-resistance. Choosing the right type of steel for your application is imperative to ensure that you get the corrosion resistance that you need.

What makes steel rust?

Understanding the science behind why some metals rust can help you understand why some other options, such as s31803 stainless steel, are more resistant than some other types.

Rust is a compound called iron oxide. It most frequently forms when iron and oxygen react to one another in the presence of moisture. Often the moisture present in the air is enough.

In some other cases, iron and the chloride in a salt water environment can react to create rust. This can be visible in rebar used in a seawall where it is repeatedly exposed to salt water, which can break it down over time.

In still others, high heat can cause the chromium and carbon to bond to one another and form carbides. This can happen at temperatures between 750 and 1550 degrees Fahrenheit. Steel that is damaged due to heat is considered “sensitized;” in some cases, it can be saved through complex heat treating, but in other cases, it is permanently damaged.

How do you keep iron from rusting?

Iron is made into an amalgam with other metals to make steel. Stainless steel contains a combination of iron, carbon and chromium to prevent corrosion. It may also contain other elements such as manganese and nickel because of the qualities each of those introduce. However, the element most responsible for rust-resistance is chromium. The higher the chromium content, the less likely stainless steel is to rust. In general, stainless steel is made with anywhere from 10.5 to 30 percent chromium.

Choosing the most rust-resistant stainless steel.

There are roughly 150 types of stainless steel; these will have different compositions to accentuate different properties. Duplex stainless steel is typically a good choice. The chromium content of s31803 stainless steel is between 21 and 23 percent to ensure good corrosion resistance in a wide range of applications.

Type 304 is a popular and affordable stainless steel choice; however, it has a lower chromium content than otherwise similar 316. If your application involves exposure to moisture or saltwater, choosing the more expensive 316 can be a better and more durable investment.

We are always happy to help our customers decide which grade of stainless steel is the right one for their application. Get in touch today to discuss the best option for you.

Which stainless steel is least magnetic?

Which stainless steel is least magnetic?

Most people assume that every type of stainless steel is magnetic. It’s all made from iron, right? However, different types of stainless steel have different levels of magnetism, generally due to the steel’s chromium level. 

Ferritic vs Austenitic

Stainless steel is divided into two general types, which each have a different atomic structure. In general, ferritic stainless steel is magnetic, while austenitic types like 904L stainless steel are not. While both types of steel are iron alloys, there are critical differences in how their atoms are arranged that affect not just their levels of magnetic attraction but also other characteristics like their weldability.

In an austenitic stainless steel, the atoms are arranged in what is known as a face-centered cubic (fcc) lattice. Picture the unit cells as a cube: there are atoms at the centers of each of the cube’s faces and also at each of the eight corners of the cube. This sort of atomic arrangement is most likely to show up when the allow contains carbon, nitrogen, manganese or nickel. 

Ferritic stainless steels, by contrast, are arranged in what is known as a body-centered (bcc) lattice. Atoms are arranged at each of the eight corners of the cube. Another single atom is located in the center of the cube. Silicon, chromium and molybdenum make a bcc crystal structure most likely. 

The least magnetic steels

Stainless steel type 304, which contains 8% nickel and 18% chromium, along with small amounts of carbon, nitrogen and manganese make this steel nonmagnetic. What is interesting is that, when this steel is mechanically deformed through activities like bending or extruding, it will become partially magnetic.

Stainless steel type 904L is another popular nonmagnetic option. This type of steel contains high amounts of nickel and molybedenum, along with small amounts of carbon, manganese and phosphorus. In addition to being nonmagnetic, this type of steel is highly resistant to crevice corrosion and stress corrosion cracking. It’s highly weldable and formable. 

Magnetized or Unmagnetized?

Ferritic steels typically start off unmagnetized. However, if they are exposed to a magnetic field, they will become magnetized. Even after being removed, they will remain magnetic to some degree. Nonmagnetic steels do not have this property, and can be exposed to magnetic fields without any risk that they will become magnetic after exposure. 

Matching your steel choice to the job is imperative for assuring the performance that you want. We offer a range of stainless steel grades and types to ensure that you always have the exact alloy you need. Not sure what is best for your application? Get in touch. Our experts bring years of experience to the field and can help you pick the right steel for your application and your budget. 

Characteristics of 904L stainless steel

904L stainless steel is a highly durable and highly versatile material. It’s valued for its high resistance to corrosion and heat as well as its level of weldability. It’s even the choice for stainless steel Rolex watches; the high end watchmaker made the switch from 304L to 904L when they discovered that the latter would offer a better level of resistance to corrosion and pitting and make even their watches a lifelong purchase even for active wearers.

What are 904L’s best qualities?

This type of stainless steel has a low carbon content. It is high in copper to add resistance to strong acids such as sulphuric acid. The presence of high amounts of nickel makes it resistant to stress corrosion cracking. It is also highly resistant to crevice corrosion and stress corrosion cracking that can plague other types of steel. It can be used in a range of challenging environments that include warm seawater and chloride exposure. It’s a good material for both mild and aggressive conditions. 

This type of stainless steel is highly resistant to heat up to 400 degrees Celcius. It is heat treatable at temperatures that range from 1090 to 1175 Celcius when followed by rapid cooling. This sort of thermal treatment is a good choice for hardening 904L steel. 

This type of steel is non-magnetic because of its make-up. It offers high levels of weldability, formability and toughness in a range of conditions.

904L steel can be welded using all conventional methods without a need for pre-heat and post-weld heat treatments. 

What is 904L used for?

As mentioned earlier, 904L steel is the stainless steel used in the construction of Rolex watches. In industrial settings, it is valued for its high purity and its low sulfur content. A few of the places 904L is used includes:

  • Seawater cooling devices.
  • Wiring in electrostatic filtration devices.
  • Oil refinery components.
  • Gas scrubbing plant parts.
  • Machinery for pulp and paper processing.
  • Parts in machines used in sulfuric, acetic and phosphoric acid processing plants. 

At Great Plains Stainless, we carry a wide range of stainless steel tubes, pipes, fittings and flanges for all of your consumer and industrial needs. Get in touch today to learn more about what we have available and the best materials for your next project.

Understanding Pipes’ Pressure and Temperature Ratings

Every pipe and pipe fitting you work with will be classified based on its pressure temperatures rating.  You will usually see this expressed through the ASME 16.5 P-T rating system. This will give pound ratings that are written like this: #100, #500, #1000, etc.

How P-T Is Determined

The pressure or pound rating for a pipe will be dependent on the material it is made of and the design temperature. Some grades of duplex stainless steel will have higher levels of some materials than others, which can affect their malleability and other features. A material’s pressure rating will also typically change at different temperatures. A material will typically be able to take more pressure at a lower temperature and less as the temperature goes up. Not every pipe component is rated by pressure class. The areas that are are ones like flanges, gaskets and socket welded components. The pressure rating is always the rating for the weakest part of a system. The goal in design is to make the weakest component of any system strong enough to easily hold up to the pressures and temperatures it will be exposed to.

Pipe Thickness and Pressure

The thickness of a pipe is also involved in the calculations when choosing materials. Pipe thickness can be calculated through either the flange rated method (which is also called the P/S ratio method) or the exact design conditions that are provided. The maximum pressure and temperature are calculated for the greatest thickness that is required. This is the thickness that is needed to stand up to the pressure and temperature of the system you are designing.

The flange rated method is considered the most conservative approach. It may provide more thickness than is required, but it is also more uniform. It will not lead to various thicknesses throughout the project, which means that the materials will be easier to procure. You will also be secure that every component has the strength and resistance that is needed for the application at hand.

Choosing Your Materials

Not sure what grade you need for the job? We carry all of the following and more:

  • 310 Stainless steel
  • 309 Stainless steel
  • 410 Stainless steel
  • 317 Stainless steel
  • 321 Stainless steel
  • 446 Stainless steel
  • 904L Stainless steel
  • 2205 Stainless steel
  • S31803 Stainless steel
  • N08904 Stainless steel

We can help you determine which grade offers both the best value for your money and the qualities that you need for your application. Send us a note through the on-site chat or give us a call to learn more.