DESCALING, ETCHING AND ACID CLEANING OF HEAT RESISTANT ALLOYS

The choice of the proper solution for descaling, etching or acid cleaning is determined by, among other factors, the type of alloy, the alloy constituents and the ability of the alloy to be hardened by thermal treatment. The recommendations and suggestions given below are based upon our laboratory tests and field use experience. However, since field conditions, individual part history and thermal history, and many other conditions vary beyond our control, the final selection of processing solutions and sequences must be the responsibility of the user, based on his tests and experience. These recommendations are given as general guidelines only, to assist in the user evaluation and selection process.

NITRADD Solutions

(% by volume)

Solution

HNO3

H2O

H3PO4

Nitradd

A

34

52

--

14

B

40

53

--

7

C

47

47

--

6

G

80

--

--

20

E

10

69

15

6

X

12

81

--

7

Solution D Turco 4316 Scale Conditioner:

Prepare a 100 g/L solution by slowly and cautiously adding the appropriate amount of Turco 4316 to an amount of tepid water equivalent to 75% of the final tank volume, while mixing. Mix until all solids are completely dissolved. Carefully add enough water to bring the solution to its final volume. Operate at 130 to 135C.

Note: This product is also available in a ready-to-use, predissolved form as Turco 4316-L.

Solution F Turco 4338 Scale Conditioner

Prepare a 240g/L to 300g/L solution by slowly and cautiously adding the appropriate amount of Turco 4338 to an amount of water equivalent to 75% of the final tank volume, while mixing. Mix until all solids are completely dissolved. Carefully add enough water to bring the solution to its final volume.

Note: Although not identical in composition, a similar solution with equivalent effectiveness may be prepared by mixing equal volumes of Turco 4338-L, Part 1 and Part 2, 20% each, with water, at 60%, such that the total final volume is the desired working volume of the tank. Operate at 90 to 95C.

ETCHING AND DESCALING

  1. Chrome and chrome-nickel, nickel-molybdenum and nickel-cobalt alloys:
    1. Use Solution A at 20 to 25C for 15 to 20 minutes
      1. 18-8 chrome-nickel steels: 301, 302, 303,304, 305, 316, 317, 318, 321,347, 348
      2. 19-9 chrome-nickel steels: 19-9DL, 19-9DX
      3. High nickel chromium alloys: Inconel, Inconel X, Nimonic 75, Inconel W, etc. (Processing time may be increased to 25 minutes, as required.)
    2. Use Solution A at 45 to 50C for 15 to 25 minutes
      1. 20-10 chrome-nickel alloys: 308, 309, 310, 314, etc. (Processing time may be increased to 30 minutes, as required.)
      2. Chrome-nickel-cobalt alloys: N-155 (Processing time may be increased to 30 minutes as required.)
      3. Cobalt-chrome-nickel alloys: S-816, HS-25(L605), etc.
      4. Nickel-molybdenum alloys: Hastelloy B, Hastelloy C, Hastelloy X, etc.
      5. Nickel-cobalt alloys: HS-27, Rene41, UDIMET500, etc.
  2. Heat hardenable chrome-nickel alloys:
    1. Use Solution B at 22 to 30C for 10 to 20 minutes
      1. Heat hardenable chrome-nickel alloys: 15-7 Mo, 17-7 PH, AM350, A-286, etc.
      2. (Solution E may also be used where minimal weight loss is desired.)
      3. Titanium alloys (all)
    2. Use Solution C at 22 to 30C for 10 to 20 minutes
      1. (This bath should not be used as a common pickel for titanium and other alloys. Accelerated action and pitting of titanium may result.)
      2. High nickel alloys, copper alloys
    3. Use Solution E at 45 to 50C for 10 to 20 minutes
      1. 98%+ nickel
      2. Nickel-copper alloys: Monel, Monel K, Monel R, Monel KR (Processing times may be increased to 25 minutes as required.)
      3. Copper alloys (all) (Processing times may be increased to 25 minutes, as required.)
      4. (This bath may also be used for heat hardenable chrome-nickel alloys)
  3. High silica aluminum castings
    1. Use Solution G at 15 to 25C for 30 seconds to 3 minutes
      1. (Used to deoxidize/desmut castings. Parts must be dry to avoid dilution of solution. Solution becomes corrosive on dilution.)

    SCALE CONDITIONING

    Some very obdurate, tenacious scales may require conditioning prior to pickling for optimum results. This condition is generally encountered on parts that are heavily scaled from heat treatment or exposure to high temperatures (>500C). These solutions may not be used on reactive metals such as aluminum or copper alloys. These are used by immersing parts in the scale conditioning solution for the indicated time, thoroughly rinsing the parts with cool water, and then pickling in the solution indicated above.

  4. Steels, stainless steels, titanium alloys, magnesium alloys
    1. Use Solution D at 30 to 40C for 10 to 45 minutes
      1. (10 to 15 minutes for light, low temperature scale; up to 45 minutes for difficult, high temperature scale.)
  5. Steels, stainless steels, titanium alloys, nickel alloys, cobalt alloys
    1. Use Solution F at 90 to 95C for 30 to 60 minutes

    PICKLING

  6. Stainless steel honeycomb core, such as PH 15-7 Mo, 17-7 PH, or other heat hardenable alloys
    1. Use Solution X at 15 to 40C for sufficient time to remove surface discoloration

N0TICE:

The above information and recommendations are based upon our laboratory tests and field use experience with these and similar products. However, since conditions of actual use are beyond our control, any recommendations are made without warranty, express or implied. Manufacturer’s and seller’s sole obligation shall be to replace those portions of any products shown to be defective. Neither shall be liable for any loss, damage or injury, direct or consequential, arising from the use of these products.

New 6/99
TDB #496