Mr Hegde,
Inconel 690 (UNS N06690) is an all austenitic alloy which is covered under Sec-II Part-B,SB-163. Krupp Nicrofer 6030 is the product of Thyssen Krupp VDM , one of the key players for this type of alloy products. Although being austenitic, Inconel 690 alloy have fairly high UTS and could work harden considerably while cold bending. Hence manufacturer recommends post forming heat treatment as follows:-
Cold working:- For cold working the material should be in the annealed condition. Nicrofer 6030 has a higher work-hardening rate than austenitic stainless steels. This should be taken into account when selecting forming equipment. Interstage (Intermediate) annealing may be necessary with high degrees of cold forming. After cold working with more than 10% deformation soft or solution annealing is required before use.
Soft annealing of Nicrofer 6030 should be carried out in the temperature range 1020 to 1070 °C (1870 to 1960 °F), preferably at about 1040 °C (1900 °F).
Solution annealing for improved creep strength is carried out at 1080 to 1150 °C (1980 to 2100 °F). Water quenching or rapid air cooling is recommended for thicknesses above about 1.5 mm (0.06 in.) and is essential for maximum corrosion resistance.
If the design code for the exchangers is ASME ,Sec VIII, DIV-1, then the requirements of UNF-79 would apply for post forming heat treatments, provided the tubes are bent in the shop.
Should the tubes be procured in finished condition( U-Bundle) from the mill then the supplementary conditions of SB-163 would apply.
The O D of the tubes and wall thickness are very small. Hence without proper tube bending devices U-bent areas could get flattened. See the attached Special Metals brochure for your added reference.
Thanks.
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Email-pgoswami@sympatico.ca,
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of PB HEGDE
Sent: Tuesday, July 27, 2010 2:11 AM
To: materials-welding@googlegroups.com
Subject: [MW:6138] Inconel 690 Tube Bending
Dear Friends
I have a query and request you to give your opinion
a) One of the Heat exchangers, we want to use U tubes of Inconel 690 having OD of 13mm and 19mm with thk of 1.2mm
b) Straight tubes shall be purchased and bending shall be carried in house or at tube manufacturer
c) I want to know does it require any solution annealing after U bending ? and if Yes what will be cooling media and method to avoid flattening of tube near bend
d) What are the testing require to ensure correct metallurgical , physical and mechanical properties
Warm regards
Hegde P.B.
+919714714803
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