Metal Bellows Correctedn 7/11/00 2:42 PM Page 19
MATERIALS – COMMON METALLURGICAL PROBLEMS
Failure Mode Cause Frequently Used Solution
Chloride Stress Corrosion Chlorides acting on highly stressed Use a high nickel alloy like alloy 600
Cracking austenitic stainless steel bellows or alloy 625.
(T304, T321, etc.)
Carbide Precipitation Chromium carbides form in Use a stabilized stainless steel (T321
unstabilized stainless steels (T304, or T347) or a low carbon stainless
T316) at high temperature (over 700 steel (T304L) or another high alloy
F) causing loss of corrosion resistance material that is less affected by
at the grain boundaries. carbide precipitation.
Pitting Corrosion Galvanic action causes holes to form Use a bellows material containing
in a bellows, usually from acids. molybdenum T316, Alloy 825, Alloy
625) or one of the specialty materials
such as zirconium tantalum or
titanium.
Dew Point Corrosion Liquid acid precipitates out of a sulfur Insulate the bellows to insure it
rich flue gas stream in contact with operates above dew point in service
the bellows element that operates or install a “Hot Blanket” to maintain
just below the dew point for acid a constant bellows skin temperature
formation. that is above dew point.
Standard Material Specifications
BELLOWS MATERIAL DATA
For Bellows Shown In This Catalog
Senior Flexonics Pathway engineers can form bellows from most ductile
ASTM MATERIAL Part Number
Designation Designation materials that can be welded by the automatic TIG butt welding process
A240 T304 304 (Catalog Standard) that results in a homogenious ductile weld structure.
A240 T304L 304L
Companies specifying and purchasing bellows must give careful
A240 T309s 309s
A240 T316 316
consideration to the selection of bellows material. When in doubt,
A240 T316L 316L
consult with basic supplier mill Metallurgist. Senior Flexonics does not
A240 T317 317
A240 T317L 317L
take responsibility for alloy selection.
A240 T321 321
A240 T347 347
B688 AL6XN AL6XN
A240 7Mo plus 7 Mo plus Use of these material codes as a suffix in the Catalog part number will
A240 2205 2205
designate the bellows material that will be supplied by Senior flexonics
A625 904L 904L
Pathway.
B463 20Cb 20Cb
A240 255 255 *ASME “ SA” or “ SB” materials are inventoried and are available upon request
B536 330 330
A240 253MA 253MA
All bellows material purchased by Senior Flexonics Pathway is “mill
B435 230 230
annealed” in accordance with ASTM or ASME specifications. Senior
B162 200 (Nickel) 200 Flexonics Pathway does not perform any other heat treating operations
B162 201 (Nickel) 201
before welding, after welding before forming convolutions or after
B127 Alloy 400 (Monel) 400
forming convolutions unless specified by purchaser. Heat treatment of
B168 600 (Inconel) 600
B443 617 617
bellows after forming convolutions can lower bellows spring rate
B443 625 LCF 625 LCF
“squirm” pressure, and cycle life. Senior Flexonics Pathway does not
B409 800 800 recommend heat treatment be performed unless the bellows is operating
B409 800H 800H
at high temperatures where time dependent properties of creep and stress
B424 825 825
rupture become significant.
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