ASTM A688
Basic Info
ASTM A688 outlines the standard for welded austenitic stainless steel feedwater heater tubes including those bent, if specified, into the shape of U-tubes. This standard specifies the materials, dimensions, and mechanical properties of tubes used in power generation equipment for heating feedwater. It ensures the quality and performance of stainless steel tubes in high-temperature and high-pressure environments.
Characteristics
Welded Austenitic Stainless Steel Feedwater Heater Tubes: Designed for use in the construction of boilers, superheaters, heat exchangers, or condensers.
Corrosion Resistance: The austenitic stainless steel construction provides excellent resistance to corrosion in various environments.
Specific Application: Primarily used in feedwater heater systems in power plants and other industrial applications.
Precision Welding: The tubes are typically welded using precision techniques to ensure high-quality and leak-free performance.
ASTM A688 Data Sheet
Dimensions and Tolerances
Equivalent Grades
Chemical Composition
Mechanical Properties
Fabrication and Welding
Dimensions and Tolerances
Round Tube
Width: 6.35 – 101.6 mm
Thickness: 0.38 – 3.05 mm
Tolerances: OD and wall thickness: ±10% or ±0.15 mm, whichever is greater
Square Tube
Width: 12.7 x 12.7 mm – 101.6 x 101.6 mm
Thickness: 0.38 – 3.05 mm
Tolerances: Width and thickness: ±10% or ±0.15 mm, whichever is greater
Rectangular Tube
Width: 12.7 x 25.4 mm – 50.8 x 101.6 mm
Thickness: 0.38 – 3.05 mm
Tolerances: Width and thickness: ±10% or ±0.15 mm, whichever is greater
Equivalent Grades
Germany
DIN 1.4401
Japan
JIS SUS316
China
GB 0Cr17Ni12Mo2
Chemical Composition
Carbon (C)
Composition: 0.030% max
Manganese (Mn)
Composition: 2.00% max
Phosphorus (P)
Composition: 0.045% max
Sulfur (S)
Composition: 0.030% max
Silicon (Si)
Composition: 0.75% max
Chromium (Cr)
Composition: 16.0 – 18.0%
Nickel (Ni)
Composition: 11.0 – 14.0%
Molybdenum (Mo)
Composition: 2.0 – 3.0%
Nitrogen (N)
Composition: 0.10% max
Mechanical Properties
Tensile Strength, min
515 MPa (75 ksi)
Yield Strength, min
205 MPa (30 ksi)
Elongation in 2 inches (50.8 mm), min
35%
Hardness, max (Brinell)
192 HBW or 207 HRB
Hardness, max (Rockwell B)
90 HRB
Fabrication and Welding
Welding
Use low heat input during welding to minimize distortion and prevent carbide precipitation.
Preheat and post-weld heat treatment are not required.
Use filler metals that match the base metal composition, such as AWS E316/E316L electrodes for welding.
Ensure adequate shielding gas coverage, typically argon or a mixture of argon and helium.
Use stringer bead welding techniques for optimal penetration and strength.
Avoid excessive interpass temperatures to prevent sensitization and intergranular corrosion.
Forming
ASTM A688 stainless steel tubes can be cold formed using standard techniques such as bending, flanging, and roll forming.
Avoid severe forming operations that may induce excessive strain hardening or cracking.
Annealing may be required after cold forming to restore ductility and minimize residual stresses.
Machining
ASTM A688 stainless steel tubes can be machined using conventional methods such as turning, milling, drilling, and tapping.
Use sharp tools and low cutting speeds to minimize work hardening and tool wear.
Lubricants or coolants may be used to improve surface finish and tool life.
Heat Treatment
ASTM A688 stainless steel tubes are typically supplied in the solution annealed condition.
Heat treatment is generally not required after fabrication or welding.
If necessary, annealing can be performed at temperatures between 1010°C (1850°F) and 1120°C (2050°F), followed by rapid quenching in water or air.
Annealing helps to relieve residual stresses and restore mechanical properties.
Cleaning and Passivation
Clean ASTM A688 stainless steel tubes thoroughly after fabrication to remove contaminants such as grease, oil, and dirt.
Passivate the surface using an appropriate chemical treatment to enhance corrosion resistance and remove any surface oxides.
Passivation methods include immersion in citric acid or nitric acid solutions, followed by rinsing and drying.
Corrosion-Resistant Guardians: The Reliability of ASTM A688 Stainless Steel Tubes
ASTM A688 stainless steel tubes stand out for their remarkable corrosion resistance, setting a high standard for reliability in challenging environments. Engineered with elevated levels of chromium and nickel, these tubes form a protective oxide layer that shields against corrosion, ensuring longevity even in the most corrosive atmospheres. This inherent resistance makes them indispensable in marine, chemical, and industrial applications where durability is paramount. Customers benefit from reduced maintenance costs and prolonged equipment life, thanks to the superior protection offered by ASTM A688 tubes. Their ability to withstand harsh conditions without compromising performance makes them a preferred choice for critical applications such as heat exchangers and condensers. In essence, ASTM A688 stainless steel tubes provide peace of mind, knowing that infrastructure and equipment remain resilient against corrosion, ensuring uninterrupted operations and long-term cost savings.
