ASTM A928 / A928M Abstract
This specification covers standard requirements for ferritic/austenitic (duplex) stainless steel pipe that is electric fusion welded with a ddition of filler metal suitable for corrosive service. Heat treatment shall be performed after weldi ng and in accordance with specified temperature and quench conditions. conditions. Several grades of ferritic/austenitic steel shall conform to the requirements of the applicable specification and grade designation. Heat and product analyses shall be conducted and shall conform to t he requirements for the particular grade. The plate used in making the pipe shall sha ll conform to the required tensile properties. The steel pipe shall undergo several mechanical tests t ests including transverse tension test, t est, transverse guided-bend guided-bend test, nondestructive test, hydrostatic test, and nondestructive nondestructive electric test. This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standar d; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.
1.
Scope
1.1 This specification covers electric-fusion-welded steel pipe suitable for corrosive service. Note 1²The dimensionless designator NPS (nominal pipe size) has been substituted in this specification for traditional terms such as nominal diameter, size, and nominal size. 1.2 This specification covers grades of ferritic/austenitic steel as indicated in Table 1. T The he selection of the proper alloy and requirements for heat treatment shall be at the discretion of the purchaser, dependent on the service conditions to be encountered. 1.3 Five classes of pipe are covered as follows: 1.3.1 Class 1²Pipe shall be double welded by processes using filler metal in all passes a nd shall be radiographed ra diographed completely. completely. 1.3.2 Class 2²Pipe shall be double welded by processes using filler metal in all passes. No radiograph is required. 1.3.3 Class 3²Pipe shall be single welded by processes using filler metal in all passes and shall be radiographed ra diographed completely. completely. 1.3.4 Class 4²Same as Class 3, except except that t he weld pass exposed to the inside pipe surface is permitted to be made without the addition of filler metal (see 6.2.2.1 and 6.2.2.2). 1.3.5 Class 5²Pipe shall be double welded by processes using filler metal in all passes and shall be spot ra diographed. diographed. 1.4 Supplementary requirements covering provisions provisions ranging from additional t esting to formalized procedures proc edures for manufacturing practice are provided. Supplementar Supplementary y Requirements S1 through S4 are included as options to be specified in the purchase order when desired.
1.5 The values stated in either SI units or inch-pound units are to be regarded s eparately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. The inch-pound units shall apply unless the M designation of the specification is specified in the order.
2. Referenced Documents( purchase separately)
The documents listed below are referenced within the
subject standard but are not provided as part of the standard.
ASTM Standards
A240/A240M Specification for Chromium and Chr omium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications A480/A480M Specification for General Requirements for F lat-Rolled Stainless and HeatResisting Steel Plate, Sheet, and Strip A941 Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys A999/A999M Specification for General Requirements for Alloy and Stainless Steel Pipe E426 Practice for Electromagnetic (Eddy-Current) Examination of Seamless a nd Welded Tubular Products, Austenitic Stainless Steel and Similar Alloys ASME Boiler and Pressure Vessel Code
SectionIX,WeldingQualifications AWS Specifications
A5.30 Consumable Weld Inserts for Gas Tungsten Arc Welding
Index Terms
arc welded steel pipe; corrosive servic e; duplex (austenitic-ferritic) stainless steel; fusion welded steel pipe; steel pipe; welded steel pipe; Austenitic stainless steel pipe--specifications; Corrosive service applications--pipe (steel); Duplex stainless steel--specifications; Electricfusion-welded steel pipe; Ferritic steel pipe--specifications; Filler metals; Stainless steel pipe-specifications; ICS Number Code 25.160.40 (Welding joints and welds)
Duplex Stainless Steel Duplex stainless steels are called ³duplex´ because they have a two-phase microstructure consisting of grains of ferritic and austenitic stainless steel. The picture shows the yellow austenitic phase as ³islands´ surrounded by the blue ferritic phase. When duplex stainless steel is melted it solidifies from the liquid phase to a completely ferritic structure. As the
material cools to room temperature, about half of the ferritic grains transform to austenitic grains (³islands´). The result is a microstructure of roughly 50% austenite and 50% ferrite.
Duplex stainless steels have a t wo-phase microstructure of austenite and f errite grains .
The duplex structure gives this family of stainless steels a combination of attractive properties: Strength: Duplex stainless steels are about twice as strong as regular austenitic or ferritic stainless steels. Toughness and ductility: Duplex stainless steels have significantly better toughness and ductility than ferritic grades; however, they do not reach the excellent values of a ustenitic grades. Corrosion resistance: As with all stainless steels, corrosion resistance depends mostly on the composition of the stainless steel. For chloride pitting and crevice corrosion resistance, their chromium, molybdenum and nitrogen content are most important. Duplex stainless steel grades have a range of corrosion resistance, similar to the range for austenitic stainless steels, i.e from Type 304 or 316 (e.g. LDX 2101©) to 6% molybdenum (e.g. SAF 2507©) stainless steels. Stress corrosion cracking resistance: Duplex stainless steels show very good stress corrosion cracking (SCC) resistance, a pr operty they have ³inherited´ from the ferritic side. SCC can be a problem under certain circumstances (chlorides, humidity, elevated temperature) for standard austenitics such as Types 304 and 316. Cost: Duplex stainless steels have lower nickel a nd molybdenum contents than their austenitic counterparts of similar corrosion resistance. Due to the lower alloying content, duplex stainless steels can be lower in cost, especially in times of high alloy surcharges. Additionally, it may often be possible to reduce the section thickness of duplex stainless steel, due to its increased yield strength compared to austenitic stainless steel. The combination
can lead to significant cost and weight savings compared to a solution in austenitic stainless steels.
Topics Covered Background ASTM A240/A240M Alloy Designations Chemical Composition of Duplex stainless steel Properties of Duplex stainless steel Mechanical Properties of Duplex stainless steel Physical Properties of Duplex stainless steel Corrosion Resistance of Duplex stainless steel Heat Resistance of Duplex stainless steel Fabrication of Duplex stainless steel Heat Treatment of Duplex stainless steel Machinability Welding of Duplex stainless steel Applications of Duplex stainless steel Supplied Forms
Background Duplex stainless steelare extremely corrosion resistant, work hardenable alloys. Their microstructures consist of a mixture of austenite and ferrite phases. As a result, duplex stainless steels display properties characteristic of both austenitic and ferriticstainless steels. This combination of properties can mean some compromise when compared with pure austenitic and pure ferritic grades. Duplex stainless steel are in most cases, tougher than ferriticstainless steel. Strengths of duplex stainless steels can in some cases be double that for austenitic stainless steels. Whilst duplex stainless steelare considered resistant to stress corrosion cracking, they are not as resistant to this form of attack as ferritic stainless steel. However, the corrosion resistance of the least resistant Duplex stainless steel is greater than that for the most commonly used grades of stainless steel, i.e. 304 and 316. Duplex stainless steelare also magnetic, a property that can be used to easily differentiate them from common austenitic grades of stainless.
ASTM A240/A240M Property data given in this document is typical for flat rolled products covered by ASTM A240/A240M. ASTM, EN or other standards may cover products sold by Aalco. It is reasonable to expect specifications in these standards to be similar but not necessarily identical to those given in this article.
Alloy Designations Due to excellent corrosion resistance and high strength, the most widely used duplex stainless steel is 2205. The name 2205 comes from a typical composition of 22% Chromium and 5% Nickel. Other designations for 2205 are given in the table below. UR52N+ is a popular ³super duplex´ grade that has high strength and exceptional corrosion resistance.
This grade differs in composition to 2205 stainless steel in that it contains an addition of copper. This gives greatly improved resistance to hot chlorides and strong reducing acids, like sulphuric acid. UR52N+ is the widely used registered trade name of the Usinor group. Other designations it is known by are given in the table below. There are many other duplex stainless steel most of which are proprietary grades developed and produced by individual manufacturers. T ab le 1. Some standard designations for duplex stainless steel alloys
Euronorm
UNS
BS S31803
1.4462
S32205 S32520
1.4507
S32550
En
Grade
318S13
-
2205
-
-
UR52N+
Chemic al Composition of Duplex stainless steel T ab le 2. Typical chemical composition for two duplex stainless steel alloys
%
2205
UR52N+
C
0.03 max
0.03 max
Mn
2.0
1.5
Si
1.0
0.8
P
0.03
0.035
S
0.02
0.02
Cr
21-23
24-26
Mo
2.5-3.5
3.0-5.0
Ni
4.5-6.5
5.5-8.0
N
0.08-0.2
0.2-0.35
Cu
-
0.5-3.0
Properties
of Duplex stainless steel
Mech anic al
Properties
of Duplex stainless steel
T ab le 3. Typical mechanical properties of two duplex stainless steel alloys
Grade
2205
UR52N+
Tensile Strength (MPa)
620
770
Proof Stress 0.2% (MPa)
450
550
Elongation A5 (%)
25
25
Hardness Rockwell C
31
-
Physic al Properties
of Duplex s tainless steel
T ab le 4. Typical mechanical properties of two duplex stainless steel alloys
Property
2205 3
UR52N+
Density (g.cm )
7.805
Modulus of Elasticity (GPa)
200
Electrical Resistivity (.m) Thermal Conductivity (W/m.K) Thermal Expansion (m/m.K)
7.810 205 -6
0.085x10
19 at 100°C -6
13.7x10
to 100°C
0.085x10-6 17 at 100°C 13.5x10-6 to 200°C
Corrosion Resistance of Duplex s tainless steel Duplex stainless steelare extremely corrosion resistant. They have high resistance to intergranular corrosion. Even in chloride and sulphide environments, Duplex stainless steel exhibit very high resistance to stress corrosion cracking. The super duplex grades are even more resistant to corrosion.
Heat Resistance of Duplex stainless steel The high chromium content of Duplex stainless steel that p r otects against corrosion, causes embrittlement at temperatures over about 300°C. At low temperatures duplex stainless steels have better ductility than the ferritic and martensitic grades. Duplex grades can readily be used down to at least -50°C.
Fabric ation of Duplex stainless steel Fabrication of all stainless steel should be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before use. These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.
Heat Treatmen t of Duplex stainless steel Duplex stainless steel cannot be hardened by heat treatment. They can however be work hardened. Solution treatment or annealing can be done by rapid cooling after heating to around 1100°C.
Machin ability Although machinable, the high strengths of Duplex stainless steelmakes machining difficult. As an example, machining of 2205 is around 20% slower than for 304. Machining can be enhanced by using the following rules:
y
Cutting edges must be kept sharp. Dull edges cause excess work hardening.
y
Cuts should be light but deep enough to prevent work hardening by riding on the surface of the
material.
y
Chip breakers should be employed to assist in ensuring swarf remains clear of the work
y
L ow thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This
means coolants and lubricants are necessary and must be used in large quantities.
Welding
of Duplex s tainless steel
Duplex stainless steelhave good weldability. All standard welding processes can be used. They are not quite as easily welded as the austenitic grades but low thermal expansion in duplex grades reduces distortion and residual stresses after welding. The recommended filler material for 2205 stainless steel is 2209.
Applications of Duplex stainless steel Duplex stainless steel are typically used in:
y
Chemical processing, transport and storage
y
Oil and gas exploration and offshore rigs
y
Oil and gas refining
y
Marine environments
y
Pollution control equipment
y
Pulp & paper manufacturing
y
Chemical process plant
Supplied Forms
Aalco typically supplies 2205 duplex stainless steel in the following forms:
y
Round bar
y
CCP plate
y
Quarto plate
y
Duplex stainless steels have a mixed microstructure of austenite and f errite, the aim usually being to produce a 50/50 mix, although in commercial alloys the ratio may be 40/60. Duplex stainless steels have r oughly twice the strength compared to austenitic stainless steels and also improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterized by high chromium (19±28%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. Duplex grades are characterized into groups based on their alloy content and corrosion resistance. Lean duplex refers to grades such as UNS S32101 (LDX 2101), S32304, and S32003. The standard duplex is 22% chromium with S31803/S32205 known as 2205 being the most widely used. Super duplex refers to 25% chromium grades such as S32760 ( Zeron 100), S32750 (2507), and S32550 (Ferralium). Hyper duplex refers to higher chromium grades such as S32906. The properties of duplex stainless steels are a chieved with an overall lower alloy content than similar-performing super-austenitic grades, making their use cost-effective for many applications.
