Inconel 625 Flange & Alloy 625 Weld Overlay

Characteristics & Applications

The Inconel 625 flanges generally refer to pipe flanges made from ASTM B564 UNS N06625 forgings or ASTM B443 Grade N06625 plates. Inconel 625 is the famous proprietary tradename of alloy 625, which has the nominal chemical designation of 60Ni-22Cr-9Mo-3.5Nb. It is a nickel-chromium-molybdenum alloy with an addition of niobium that acts with the molybdenum to stiffen the alloy’s matrix and thereby provide high strength without a strengthening heat treatment. The alloy resists a wide range of severe corrosive environments and is especially resistant to pitting and crevice corrosion. It is usually used at service temperatures ranging from -325°F [-198°C] to 1200°F [649°C] in annealed condition. The Inconel alloy 625 flanges can be used in chemical and petrochemical processing, marine engineering, pollution-control piping, nuclear power systems, coal gasification and liquefaction piping, as well as pulp and paper industries.

Chemical Composition Requirements

Element	Composition, %
Ni	≥58.0
Fe	≤5.0
Mn	≤0.50
C	≤0.10
Si	≤0.50
S	≤0.015
Cr	20.0-23.0
Al	≤0.4
Ti	≤0.4
Nb+Ta	3.15-4.15
Mo	8.0-10.0
P	≤0.015

*The composition requirements for Inconel 625 flanges made of ASTM B564 or ASTM B443 Gr. N06625.

Mechanical Property Requirements

ASTM B564 Gr. N06625	M.S.T≤4"	4"＜M.S.T≤10"
Tensile Strength min. MPa [ksi]	827 [120]	758 [110]
Yield Strength min. MPa [ksi]	414 [60]	345 [50]
Elongation in 2", min. %	30	25

*M.S.T: maximum section thickness of Inconel 625 flanges made from ASTM B564 Gr. N06625 forgings, applicable to all flange types.

ASTM B443 Gr. N06625	Requirements
Tensile Strength min. MPa [ksi]	827 [120]
Yield Strength min. MPa [ksi]	414 [60]
Elongation in 2", min. %	30

*Mechanical properties for Inconel 625 flanges made from ASTM B443 UNS N06625 Grade 1 (annealed) plates, applicable to flanges without hub.

Pressure-Temperature Ratings

Temp. °F	150# psi	300# psi	400# psi	600# psi
-20-100	290	750	1000	1500
200	260	750	1000	1500
300	230	730	970	1455
400	200	700	930	1395
500	170	665	885	1330
600	140	605	805	1210
650	125	590	785	1175
700	110	570	755	1135
750	95	530	710	1065
800	80	510	675	1015
850	65	485	650	975
900	50	450	600	900
950	35	385	515	775
1000	20	365	485	725
1050	-	360	480	720
1100	-	325	430	645
1150	-	275	365	550
1200	-	205	275	410
1250	-	165	220	330
1300	-	120	160	240

*P-T ratings for Inconel 625 flanges made of ASTM B564 Gr. N06625 or ASTM B443 Gr. N06625 in annealed condition: Class 150, Class 300, Class 400, Class 600.

Temp. °F	900# psi	1500# psi	2500# psi
-20-100	2250	3750	6250
200	2250	3750	6250
300	2185	3640	6070
400	2095	3490	5820
500	1995	3325	5540
600	1815	3025	5040
650	1765	2940	4905
700	1705	2840	4730
750	1595	2660	4430
800	1525	2540	4230
850	1460	2435	4060
900	1350	2245	3745
950	1160	1930	3220
1000	1090	1820	3030
1050	1080	1800	3000
1100	965	1610	2685
1150	825	1370	2285
1200	615	1030	1715
1250	495	825	1370
1300	360	600	1000

*P-T ratings for Inconel 625 flanges made of ASTM B564 Gr. N06625 or ASTM B443 Gr. N06625 in annealed condition: Class 900, Class 1500, Class 2500.

Alloy 625 Weld Overlay for Wetted & Sealing Surfaces

Due to the superior corrosion resistance and heat resistance, Inconel 625 flanges are a good choice for many piping applications involving severe & harsh service conditions. However, the disadvantage is that the nickel alloy is very expensive, especially when the flange size is large. The advent of weld overlay or weld cladding solved such a problem. The flange will be made from a conventional carbon and low alloy steel and is called “base metal”. All wetted and sealing surfaces of the flange that are in contact with the fluid flowing through, shall be deposited with one or several layers of alloy 625 metal by a welding process. When the deposited Inconel 625 alloy layers (known as “cladding metal”) are cooling down, it is integrally and continuously bonded onto the flange surfaces. The excellent properties of alloy 625 are imparted to the carbon or low alloy steel base metal by such an economic method.

Alloy 625 weld overlay is usually performed using the submerged arc welding process (SAW). However, flux-cored (either self-shielded or gas-shielded), plasma arc, and electroslag welding methods can also produce weld claddings. Filler metals are available as covered electrodes, coiled electrode wire, and strip electrodes. All welding shall be performed with a procedure and welders or welding operators that are qualified in accordance with Section IX of the ASME Boiler and Pressure Vessel Code. After weld overlay, the alloy 625 cladding and base metal are brought together to form a metallurgical bond at essentially the entire interface of the two metals. The weld cladding shall be then ground or machined to the specified thickness. Generally, the filler metal of covered electrodes shall be AWS A5.11 ENiCrMo-3 for SMAW; while the filler metal of bare rods or electrodes shall be AWS A5.14 ERNiCrMo-3.