ASTM B444 Alloy 625 N06625 Seamless U Bend Tube For Refining Heat Exchangers

ASTM B444 Alloy 625 N06625 Seamless U Bend Tube For Refining Heat Exchangers

An ASTM B444 Alloy 625 Seamless U-Bend Tube is a premium, high-performance component designed for longevity and reliability in the most challenging thermal and corrosive environments found in industrial processing.

Here are some detailed breakdowns:

1. Chemical Composition Requirements of Material ASTM B444 N06625

The composition is specified by ASTM B444 and is common for all product forms (plate, tube, bar, etc.) of Alloy 625. The values are weight percent (%).

Note: The balance is Nickel (Ni). All values are maximum unless a range is given.

2. Mechanical Properties Requirements of Material ASTM B444 N06625

The mechanical properties for seamless tube and pipe are specified in ASTM B444 for material in the annealed condition. The standard specifies properties based on a sample taken from the finished product and tested longitudinally.

Important Notes on Mechanical Properties:

• Heat Treatment: To achieve these properties, the material must be supplied in the annealed condition. For Alloy 625, this typically involves a solution anneal heat treatment at a temperature around 1700°F (927°C) or higher, followed by a rapid quench (usually water). This process dissolves all secondary phases and puts the alloying elements into a uniform solid solution, optimizing corrosion resistance and ductility.
• Strength at Temperature: A key advantage of Alloy 625 is that it ages when exposed to service temperatures in the range of 600°F - 1200°F (315°C - 650°C). The Niobium (Nb) precipitates out as a strengthening phase (gamma double prime), significantly increasing its yield strength. This makes it excellent for high-temperature service. However, these aged properties are not the ones guaranteed on the test report from the mill; the mill tests the annealed, "soft" condition.
• U-Bend Specifics: For U-bend tubes, the mechanical properties are tested on the straight tube before bending. The bending process itself work-hardens and stresses the material on the outer radius of the bend. It is common practice to perform a stress relieving or full annealing heat treatment after bending to restore ductility and corrosion resistance to the highly strained bend area.

3. Why is it a "Superalloy"? Alloy 625 is renowned for:

• Exceptional Corrosion Resistance: Performs well in a vast range of severely corrosive environments, including seawater, acidic (e.g., sulfuric, phosphoric), and alkaline conditions.
• High Strength: Maintains impressive strength over a wide temperature range, from cryogenic levels up to about 1800°F (1000°C).
• Fatigue & Creep Resistance: Resists deformation under mechanical stress (fatigue) and under high temperature and constant stress (creep) for long periods.

4. Primary Application: U-Tube Bundle in Shell and Tube Heat Exchangers

The U-bend shape is specifically designed for this type of heat exchanger. A bundle of these U-tubes is inserted into a cylindrical shell. One fluid flows through the tubes (the tube side), and another fluid flows around the tubes inside the shell (the shell side). Heat is transferred between the two fluids through the tube wall.

The key reason for the U-bend is to manage thermal expansion. When the heat exchanger heats up, the long tubes expand. If they were fixed at both ends, this expansion would create immense stress, leading to tube failure, leaks, or damage to the tube sheets. The U-bend allows the entire tube to flex freely, absorbing the stress of expansion and contraction naturally.

Typical Applications

This specific component is almost exclusively used in the most demanding heat transfer applications:

• Shell and Tube Heat Exchangers: Especially the tubes in the "U-tube bundle."

Application Industries:

• Chemical Processing: Handling corrosive acids and solvents.
• Oil & Gas (Upstream & Downstream): In heat exchangers for refining, offshore platforms (seawater cooling), and sour gas service (resistant to sulfide stress cracking).
• Power Generation: In condensers, feedwater heaters, and other critical heat exchangers.
• Marine and Offshore: For seawater-cooled heat exchangers and condensers.
• Nuclear: In various auxiliary heat exchange systems.
• Pollution Control: In scrubbers and waste treatment systems.

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