Document pj4J6XrNyxDb7zmvbe33kaqX

D. R. PEINECKE MECHANICAL ENGINEERING DIVISION PITTSBURGH OFFICE - 3 ffPH was Industrie*1 Hvelena --------- ^- -yiSTRiESUTIQH^ <r> sc p. ' '') /gpg) cB -------------------^ OHS? CO AUGUST RE: POT CRADLE WEDGE TO POTSHELL INSULATION The wedge cradle design has been used at Massena (P-22S), Alumax, Noranda, and Sao Luis. A thin insulating sheet is placed between the cradle wedge and the potshell to provide a parting plane when the wedge is pulled for shell removal. The original material specification for Massena was UNARCO Style 709 graphited asbestos cloth, asbestos for temperature resistance and graphite to aid in parting. As part of our corporate attempt to eliminate asbestos bearing -materials, Massena revised this insulation to uncoated fiberglass. Sometime later, Massena began dipping the fiberglass cloth in a mixture of powdered graphite. Alumax used the UNARCO material'. Noranda used a Tetraalas graphited fiberglass. Sao Luis used a Brazilian graphited fiberglass. In 1982, Massena discovered potshell corrosion of 1/16 to 3/32" in the wedge contact area where uncoated fiberglass cloth was used. Investigation showed no substantial corrosion where asbestos or graphite coated fiberglass were used. Investigation by ATC has shown: 1. Corrosion is caused by silicon and magnesium penetration from the fiberglass to the steel at elevated temperature. This area of the shell is at 410 to 465*C because of the graphite window in the side lining. 2. Corrosion will not occur at lower temperatures. For example, there is no corrosion caused by fiberglass insulation between the bottom of the potshell and the top of the cradles. 3. Graphite promotes heat transfer away from the wedge area, which effectively elimates the corrosion problem. 4. Corrosion is limited by the quantity of silicon and magnesium in the cloth. That means that after 1/16 - 3/32" of corrosion occurs, the reaction will stop until a new piece of insulation is instedled. 5. Based on ATC testing, Pyrotek's H10B is superior to dipped fiberglass and Tetraglas in resisting corrosion. H10B is a graphite impregnated, modified fiberglas fabric. It has been stripped of sodium oxide and magnesium oxide to improve temperature rating, which may also reduce the corrosion reaction. Attached is a product data sheet for H10B. It cost $3.00/per square foot and must be cut to size and bound to prevent ravelling ALCOAO 000009092 distribution 1983 AUGUST 12 PAGE 2 Recoaaendations We recommend that Pgrotek B10B be used in this application for all future replacements. Massena ~ already using BIOB for all new replacements. Alumax - should use H10B as an asbestos substitute Noranda - may see minor corrosion from Tetraglas (based on our lab tests). Problem does not appear to warrant changing insulation at this time B10B is recommended when pots are relinedm Sao Luis - Should be aware of this problem, and may wish to have Brazilian material tested at ATC as an indicator of probable DRPtejr Attachments DISTRIBUTION: R C. McCormack J. L. McKinstry D. E. Jackson 20 AB Sao Paulo Massena cc: R. H, Lockhart/J. P. Carroll/S. J. Lindsay - Massena R* >. Horst/A* Hafeez - ATC-C B, B. Rumberger - 6 AB A R* Bendrie/J. R. Butler - Pt. Henry A. G. Rust/K, A* Isakson/L. R. Begoon/D. N. Barvey/File#J - C9 (Cradles)- 3 WPH Pt Tt Carson/Jt W. Cobes - 3 WPH ALCOAO 000009093 ASBESTOS SUBSTITUTES product data sheet &'te\r3'?*fc v. -.t Product: Color: Normally Stocked As: H-10B FIBERGLASS FABRIC BLACK Rolls 50" x 100 yds(1270mm x 30m) Temperature Limitations: Short Periods: Continuous Use: Thickness Availabilities: 2000F (1100C) 1800F ( 990C) . 050" (1.3mm) Density Availabilities: 40 oz/sq.yd (1020g/saM) Typical Uses: Weld shields, curtains, covers for high temperature gaskets. Notes: High temperature abrasion resistant cloth is ideal for cover^weld pads, and high temperature compressible gaskets. Pyrotek IflCORPORRTED - r - -v.;: .O'4*:' ' ALCQA0000009094 a