Duplex Stainless Steel U Bend Tubes ASTM A789 S32205 S31803 S32750 U bend Tubes
Duplex tubes shall be furnished in the solution annealed and water quenched condition.
·Material shall be pickled after the final anneal and water quench to provide surfaces free of discoloration.
Heat treatment of all U-bends shall be required.
o Tubes shall be heated by induction or electric resistance and held within the temperature range 1870–2010ºF (1020–1100ºC) for UNS S32205 and 1880–2060ºF (1025–1125ºC) for UNS S32750 as permitted by ASTM A789/A789M, Table 2, followed by a rapid cool below 600ºF (315.6ºC) using forced air, inert gas, or water.
§ Total time above 600ºF (315.6ºC) shall be less than 5 minutes.
§ The full tube bend and a minimum of 305mm of each leg beyond the tangent point of the bend shall be heated to the required bending temperature.
§ The controlling temperature shall be measured using a thermocouple or calibrated optical pyrometer.
§ The inside diameter (ID) and outside diameter (OD) of the tube bends shall be free of heat tint and surface oxides. This may be accomplished using an inert gas purge during heating or cooling above 600ºF (315.6ºC) or by pickling.
§ If using electric-resistance heating methods where electrodes are clamped to the tubes, clamped areas shall be visually examined for arc burns. Any burn indications shall be cause for rejection of the entire tube.
o A qualification test for the bending and heat treatment procedure shall be performed on a minimum of one U-tube sample of the smallest diameter bend and evaluated as follows:
§ Bending and heat treatment of the sample shall be performed in conformance with all production bending procedures, using the same method of heating, cooling (e.g., from the OD only), feeding, etc.
§ A radially oriented ring sample, approximately 1 inch (25 mm) long, shall be removed from the bend apex.
§ A metallographic examination shall be performed to establish volume percent ferrite content. The sample cross-section shall be polished and etched to clearly reveal a two-phase austenite/ferrite microstructure (see ASTM A923, Method A for etching procedures).
§ Ferrite content, determined using the point count test method described in ASTM E562 (minimum grid size of 100 points) or other quantitative metallographic method such as image analysis, shall be 40 to 60 volume percent.
§ The ring sample shall then be tested in accordance with the requirements of ASTM A923. The tube bend shall be free of sigma and other deleterious phases.
Permissible variations in U-tube dimensions shall be in accordance with the requirements of ASTM A803/A803M. Surface defects that violate minimum wall requirements shall be cause for rejection.
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Duplex Stainless Steel U Bend Tubes Technical Specification ASME SA789 S31803 S32205