Compositions And Methods for Pickling and Passivation of Stainless Steel Welds

Abstract

Compositions and methods for simultaneous pickling and passivation of stainless steel are presented that have exceptional shelf life, are free of hydrofluoric acid, exhibit no syneresis, and are non-corrosive to carbon steel. Moreover, contemplated compositions can be safely sprayed or otherwise applied onto various surfaces and will adhere to treated surfaces without significant runoff.

What is claimed is: 
     
         1 . A pickling and passivating composition, comprising:
 a magnesium fluoride salt, and nitric acid and/or a nitrate salt in an aqueous medium;   a water-swellable crosslinked copolymer in an amount sufficient to thicken the composition to allow for the composition to cling to a vertical surface; and   wherein the crosslinked copolymer is chemically stable in the composition such that, upon storage for at least one year, the composition exhibits substantially no syneresis and exhibits a loss in viscosity of no more than 5%.   
     
     
         2 . The composition of  claim 1 , wherein the water-swellable crosslinked copolymer is an inverse emulsion polymerization copolymer. 
     
     
         3 . The composition of  claim 2 , wherein the copolymer is prepared from an acrylamide, an acrylamidoalkyl-sulfonic acid, and/or a salt thereof, and an amine-based polyfunctional crosslinking agent. 
     
     
         4 . The composition of  claim 3 , wherein the copolymer is Solagum SH210. 
     
     
         5 . The composition of  claim 1 , wherein the composition further comprises sulfamic acid and/or calcined alumina. 
     
     
         6 . The composition of  claim 1 , wherein the magnesium fluoride salt, and nitric acid and/or a nitrate salt are formed in situ by reaction of magnesium nitrate hexahydrate and hydrofluoric acid. 
     
     
         7 . The composition of  claim 1 , wherein the copolymer is present in an amount of at least 2.5 wt %. 
     
     
         8 . The composition of  claim 1 , wherein the loss in viscosity is no more than 3%. 
     
     
         9 . The composition of  claim 1 , wherein the composition is packaged into a multi-use tube or multi-use container. 
     
     
         10 . The composition of  claim 1  in association with an instruction to spray the composition to a surface. 
     
     
         11 . A method of preparing a pickling and passivating composition, comprising:
 dissolving magnesium nitrate hexahydrate in an aqueous medium to form a magnesium nitrate solution;   adding hydrofluoric acid to the magnesium nitrate solution to form a magnesium fluoride precipitate and nitric acid; and   adding a water-swellable crosslinked copolymer in an amount sufficient to thicken the composition to allow for the composition to cling to a vertical surface;   wherein the crosslinked copolymer is chemically stable in the composition such that, upon storage for at least one year, the composition exhibits substantially no syneresis and exhibits a loss in viscosity of no more than 5%.   
     
     
         12 . The method of  claim 11 , wherein the water-swellable crosslinked copolymer is a copolymer is an inverse emulsion polymerization copolymer. 
     
     
         13 . The method of  claim 12 , wherein the copolymer is prepared from an acrylamide, an acrylamidoalkyl-sulfonic acid, and/or a salt thereof, and an amine-based polyfunctional crosslinking agent. 
     
     
         14 . The method of  claim 13 , wherein the copolymer is Solagum SH210. 
     
     
         15 . The method of  claim 11 , further comprising a step of adding sulfamic acid and/or calcined alumina to the magnesium nitrate solution, wherein the nitric acid reacts with the sulfamic acid to form NO 2  and sulfuric acid. 
     
     
         16 . The method of  claim 11 , wherein the copolymer is added in an amount of at least 2.5 wt % of the composition. 
     
     
         17 . The method of  claim 11 , wherein the magnesium nitrate hexahydrate is dissolved in an amount of about 43 wt % of the composition, wherein the hydrofluoric acid is added in an amount of about 9 wt % of the composition, and/or wherein the water-swellable crosslinked copolymer is added in an amount of about 3 wt % of the composition. 
     
     
         18 . A method of pickling and passivating a stainless steel surface, comprising a step of applying the composition of  claim 1  to the stainless steel surface for a time sufficient to pickle and passivate the stainless steel surface. 
     
     
         19 . The method of  claim 18 , wherein the stainless steel surface comprises a weld. 
     
     
         20 . The method of  claim 18 , wherein the composition is applied by spraying or from a multi-use container.