Analysis on the current situation of world stainless steel production capacity and product development

In the past 30 years, global stainless steel output has been an average of more than 5% growth rate. In recent years, different regions of the world steel production is different, while the stainless steel production in Asia has a remarkable increase. Although the development of stainless steel in less than 100 years, but the stainless steel has been shown to be a metal material production growth is the fastest, and its production in recent years the growth rate even more than the plastic production growth rate. Stainless steel production has such a high growth rate of driving force lies in it has some of the characteristics of: resistance to corrosion and oxidation resistance and high strength to weight ratio, good rolling formability, weldability and low-temperature toughness etc..

Application direction of duplex stainless steel pipe by yaang.com

One: chemical and petrochemical processing industry in this area involves a wide range, the conditions of complex, diverse media, but also the use of duplex stainless steel earlier and more areas.

Stainless steel is defined as iron alloys with a minimum of 10.5% chromium. Other alloying elements are added to enhance their structure and properties, but fundamentally, stainless steel tubes are considered for selection as steels with corrosion resistant properties.

Selection of Stainless Steel for Water Tank Application By yaang.com

Stainless steel grades, such as the 304 (1.4301) or 316 (1.4401) types are generally suitable for storing and handling cold or unheated drinking town's waters. Localised corrosion by crevice or pitting mechanisms is not usually a hazard in properly designed, fabricated and finished tanks handling clean waters of drinking quality.

Stainless Steel for Pipework Buried in Soil By yaang.com

Soil corrosivity is often classified by its resistivity.

0 - 1500 ohm.cm	very corrosive
1500 - 2500 ohm.cm	corrosive
2500 - 5000 ohm.cm	mildly corrosive
5000 - 10000 ohm.cm	slightly corrosive
> 10000 ohm.cm	non-corrosive

Experience suggests that there is little likelihood of corrosion of 304 and 316 stainless steel with soil resistivities of 2000 ohm.cm and above if the pH is greater than 4.5 and there is clean drainage and backfill.

As with other environments, chloride levels in relation to pitting and crevice corrosion may also influence the performance of stainless steel in soils and where higher chloride levels are anticipated inland or for non-tidal coastal areas or just where a greater degree of confidence is required, type 316 would be preferred. For coastal areas and other situations where a greater degree of resistance may be required, 2205 duplex stainless steel or super duplex stainless steel can be considered.

If thought necessary, external protection such as appropriate protective casings or tapes (taking care to ensure an effective overlap to avoid crevice corrosion) may be used. Stainless steel can also be cathodically protected.

Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)

Trade Names Associated With Stainless Steel By yaang.com

Trade Names Associated With Stainless Steel table

Note, where 'Non-SS' is shown in the Nearest Grade column, this indicates that the trade name as not a stainless steel.
Use the 'Ctrl' and 'F' keys to 'find' a particular name.

Selection of Welding Consumable for Welding Stainless Steel By yaang.com

Matching the consumable to the parent material

The chemical composition of stainless steel welding consumables is matched with the base or parent material. The chemical analysis (composition) of the consumables used are usually balanced to optimise the welding process and avoid hot cracking.

Case Hardening Stainless Steel Surface Use Kolsterising By yaang.com

The Kolsterising improves the wear resistance of stainless steel surface, without degrading their corrosion resistance. There are no additions of chemical elements to the steel during the process.

It is claimed that austenitic stainless steel which contain molybdenum, such as 1.4401 (316) can also have enhanced corrosion resistance after Kolsterising.The Kolsterising process does not apply a coating on the surface but is a low temperature surface carbon diffusion treatment. Although large quantities of carbon are diffused into the surface visiblechromium carbides are not formed.

Selection of Stainless Steel for Cryogenic Application By yaang.com

Ferritic, martensitic and duplex stainless steel tend to become brittle as the temperature is reduced, in a similar way to other ferritic / martensitic steel. The austenitic stainless steel such as 304 (1.4301) and 316 (1.4401) are however 'tough' at cryogenic temperatures and can be classed a 'cryogenic steels'. They can be considered suitable for sub-zero 'ambient' temperature sometime in service specification sub-arctic and arctic application and location (typically down to -40°C).

Selection of Stainless Steel Corrosion Resistance By yaang.com

Stainless steel react with corrosive deterioration phenomenon is known as corrosion. Common metal corrosion of intergranular corrosion, pitting corrosion, stress corrosion, fatigue, corrosion and crevice corrosion.

Intergranular corrosion 
Intergranular corrosion of stainless steel corrosion in a particular medium of steel along the grain boundary of a local selective corrosion occurred. If this corrosion is the metal surface, will form micro-cracks and deep inside, until the cause breakage. In certain corrosive media (such as nitric acid, phosphoric acid, sulfuric acid, lactic acid, formic acid, hydrofluoric acid and copper sulfate, etc.), will occur along the grain boundary corrosion of stainless steel. There exist in the case of stress, intergranular corrosion may develop as intergranular stress corrosion cracking. To avoid corrosion, generally use ultra-low carbon (ω (C) ≤ 0.03%) austenitic stainless steel, duplex stainless steel and containing Titanium, Nb stabilized austenitic stainless steel.

Calculation of Pitting Resistance Equivalent Numbers PREN By yaang.com

Pitting resistance equivalent numbers (PREN) are a theoretical way of comparing the pitting corrosion resistance of various types of stainless steel, based on their chemical composition.
The PREN (or PRE) numbers are useful for ranking and comparing the different grades, but cannot be used to predict whether a particular grade will be suitable for a given application, where pitting corrosion may be a hazard.

Compared Ferritic Stainless Steel with Duplex Stainless Steel By yaang.com

High content of alloying elements, the price is relatively high, generally free of nickel ferrite. 

In summary, you can generally see the use of DSS performance and process performance of the general picture that, with its superior mechanical and corrosion-resistant comprehensive performance to win the favor of users, both to save weight, it has become an excellent resistance to save investment Corrosion Engineering.

1.4362 UNS 32304 Duplex Stainless Steel 2304 By yaang.com

Duplex Stainless Steel 2304 UNS S32304 is a 23% chromium, 4% nickel, molybdenum-free duplex stainless steel. The Alloy 2304 has corrosion resistance properties similar to 316L. Furthermore, its mechanical properties, i.e., yield strength, are twice those of304L/316L austenitic grades. This allows the designer to save weight, particularly for properly designed pressure vessel applications.

Duplex Stainless Steel 2205 S32205 S31803 By yaang.com

Duplex Stainless Steel 2205 S32205 S31803 is a 22% chromium, 3% molybdenum, 5-6% nickel, nitrogen alloyed duplex stainless steel with high general, localized, and stress corrosion resistance properties in addition to high strength and excellent impact toughness.

Duplex Stainless Steel 2205 S32205 S31803 provides pitting and crevice corrosion resistance superior to 316L or 317L austenitic stainless steel in almost all corrosive media. It also has high corrosion and erosion fatigue properties as well as lower thermal expansion and higher thermal conductivity than austenitic.The advantage of a duplex structure is that it combines the favorable qualities of aferritic alloy stress corrosion cracking resistance and high strength with austenitic alloy ease of fabrication and corrosion resistance.

LDX 2101 UNS S32101 Duplex Stainless Steel Pipe By yaang.com

LDX 2101 UNS S32101 is a lean duplex stainless steel designed for general purpose use. LDX 2101 UNS S32101 is a 21.5% chromium, 5% manganese, 1.5% nickel, 0.45% molybdenum lean duplex stainless steel with corrosion resistance superior to 304L stainless steel and comparable to 316L stainless steel.

Duplex Stainless Steel Grades Comparison Table By yaang.com

The Duplex Stainless Steel Grades Comparison Table is intended to relate former BS, EN, German and Swedish grade designations to the current EN duplex stainless steel numbers, AISI grades and UNS (Unified Numbering System) numbers. The table is based on the 'wrought' ie long products (duplex stainless steel pipes etc), pipe fitting products (duplex stainless steel eccentric reducer, etc), duplex stainless steel numbers published in EN 10088 and related standards.

The Benefits to Using Duplex Stainless Steel By yaang.com

The attractive combination of high strength, wide range of corrosion resistance, moderate weldability would seem to offer great potential for increasing the market share of duplex stainless steel. However, it is important to understand the limitations of duplex stainless steel and why they are always likely to be “niche players”. 
The advantage of high strength immediately becomes a disadvantage when considering formability and machinability. The high strength also comes with lower ductility than austenitic stainless steel grades. Therefore, any application requiring a high degree of formability, for example, a sink, is ruled out for duplex stainless steel grades. Even when the ductility is adequate, higher forces are required to form the material, for example in tube bending. There is one exception to the normal rule of poorer machinability, grade 1.4162.

Stress Corrosion Cracking SCC Of Duplex Stainless Steel By yaang.com

SCC Stress Corrosion Cracking Of Duplex Stainless Steel is a form of corrosion which occurs with a particular combination of factors:

• Tensile stress
• Corrosive environment
• Sufficiently high temperature. Normally 50 deg C but can occur at lower temperatures around 25 deg C in specific environments, notably swimming pools.

Corrosion Resistance of Duplex Stainless Steel By yaang.com

The range of duplex stainless steel allows them to be matched for corrosion resistance with the austenitic stainless steel and ferritic stainless steel grades. There is no single measure of corrosion resistance. However, it is convenient to use the Pitting Resistance Equivalent Number (PREN) as a means of ranking the grades. 
PREN = %Cr + 3.3 x %Mo + 16 x %N
The following table shows how the duplex stainless steel compare with some austenitic stainless steel and ferritic stainless steel grades.

How the Austenite Ferrite Balance Achieved By yaang.com

To understand how duplex stainless steel works, first compare the composition of two familiar steel austenitic 304 (1.4301) and ferritic 430 (1.4016).

Structure	Grade	EN Number	C	Si	Mn	P	S	N	Cr	Ni	Mo
Ferritic	430	1.4016	0.08	1.00	1.00	0.040	0.015	-	16.0/18.0	-	-
Austenitic	304	1.4301	0.07	1.00	2.00	0.045	0.015	0.11	17.5/19.5	8.0/10.5	-

The important elements in stainless steel can be classified into ferritisers and austenitisers. Each element favours one structure or the other: