Austenitic SS Alloy 20 Pipes and Tubes
Alloy 20 pipes and tubes are made with an alloy which is also known as carpenter 20 which is a
nickel-iron-chromium austenitic alloy developed for maximum resistance to acid attack,
especially in sulfuric acid and any other aggressive states which normally attack SS 316.
CHEMICAL COMPOSITION
| GRADE | Ni | Cr | Si | C | Mn | P | S | Fe | Cu | Mo | Nb | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| NICKEL ALLOY 20 | MIN % | 32 | 19 | – | – | – | – | 3 | 2 | |||
| MAX % | 38 | 21 | ≤1 | ≤0.07 | ≤2 | ≤0.045 | ≤0.035 | 35 | 4 | 3 | ≤1 |
Alloy 20 pipe specifications state as an austenitic alloy, nickel-iron-chromium molybdenum
content with the addition of copper. This extra-ordinary combination makes it ideal in
applications involving sulfuric, phosphoric, and nitric acids. The content of chromium and
molybdenum gives these pipes & tubes good pitting and crevice corrosion resistance.
Alloy 20 pipe specification
Alloy 20 Seamless Pipe : ASTM/ASME B 729 / SB 729
Alloy 20 Seamless Tube : ASTM/ASME B 729 / SB 729
Alloy 20 ERW Pipe : ASTM/ASME B 464 / SB 464
Alloy 20 ERW Tube : ASTM/ASME B 468 / SB 468
Production Process
Alloy 20 pipe specifications or UNS N08020 specs are produced such as ERW (Electric
Resistance Welded), Seamless and EFW (Electric Fusion Welding) pipes and tubes with different
forms such as round, square, rectangle, etc. having specific ends like the plain end, bevel end
and threaded end with a regular thickness of different schedule ranging from SCH 5 to SCH
XXS.
Various processes used to manufacture alloy 20 pipes and tubes are cold pilgering process,
extrusion process, tube mill process along with the piercing process which needs to be followed
by heat treatment and mechanical testing.
Fabrication and Heat treatment
Alloy 20 pipes and tubes come with good mechanical properties at both normal and elevated
temperatures, up to approximately 930°F (500°C), and are easily fabricated by usual industrial
methods. Hot forged material of alloy 20 should be heated between 2100°F and 2250°F with elevated temperature control which makes sure that the material does not fall below 1800°F
before forging.
Alloy 20 pipes and tubes can be formed by both hot-working or cold-working processes using
traditional methods. After hot working, the material needs to be annealed by heating to 1725°F
and 1850°F for a minimum of 30 minutes per inch of thickness which again needs to be
followed by a water quench required.
Properties
Alloy 20 pipes & tubes i.e. carpenter 20 pipes and tubes have excellent corrosion resistance
with better mechanical properties and comparatively easy fabrication. This alloy also has
suitable resistance in various acid environments like phosphoric acid, nitric acid, and aqueous
salt solutions.
Mechanical Properties
| Grade | Tensile Strength | Yield Strength | Elongation |
|---|---|---|---|
| [MPA] | [MPA] | (% in 50mm) min | |
| ALLOY 20 | 551 | 241 | 30 |
PHYSICAL PROPERTIES
| Grade | Density (g/cm3) | Elastic Modulus (GPa) | Co-eff of Thermal Expansion (μm/m/°C) | Thermal Conductivity (W/m.K) | Specific Heat (J/Kg.K) | Electrical Resistivity (nΩ.m) |
|---|---|---|---|---|---|---|
| 25-100°C | at 100°C | 0-100°C | ||||
| NICKEL ALLOY 20 | 8.05 | 193 | 14.7 | 12.3 | 500 | 1.08 |
Alloy 20 Pipe Welding
The addition of niobium content in alloy 20 decreases the effect of carbide precipitation while
welding, thus increasing the resistance of this alloy to intergranular corrosion. Alloy 20 pipes
and tubes exhibit exceptional resistance to stress corrosion cracking (SCC) due to chlorides.
Applications
Alloy 20 pipe fittings or UNS N08020 pipes and tubes are now a popular option for a wide
variety of sectors like the chemical, food, pharmaceutical, and plastics industries. Along with this, the superalloy is used in mixing tanks, heat exchangers, metal cleaning and pickling
equipment, and piping.
