{"id":4388,"date":"2026-07-29T09:17:27","date_gmt":"2026-07-29T09:17:27","guid":{"rendered":"https:\/\/hontitan.com\/?p=4388"},"modified":"2026-07-29T09:22:00","modified_gmt":"2026-07-29T09:22:00","slug":"titanium-grades-chemical-processing","status":"publish","type":"post","link":"https:\/\/hontitan.com\/es\/titanium-grades-chemical-processing\/","title":{"rendered":"Selecci\u00f3n de grados de titanio para el procesamiento qu\u00edmico: gu\u00eda pr\u00e1ctica para ingenieros especializados en corrosi\u00f3n"},"content":{"rendered":"<p class=\"wp-block-paragraph\">No todos los titanios ofrecen el mismo rendimiento en aplicaciones qu\u00edmicas. El grado 2 resiste de forma fiable entornos oxidantes como el \u00e1cido n\u00edtrico, pero no soporta \u00e1cidos reductores como el clorh\u00eddrico y el sulf\u00farico por encima de una concentraci\u00f3n de ~5%. El grado 7 \u2014el grado 2 con una adici\u00f3n de paladio\u2014 ampl\u00eda la resistencia a entornos de \u00e1cidos reductores hasta ~10% de HCl y ~30% de H\u2082SO\u2084 a temperatura ambiente. El grado 12 (Ti-Mo-Ni) ocupa un t\u00e9rmino medio: ofrece una mejor resistencia al cloruro y a las salmueras calientes que el grado 2, a un coste inferior al del grado 7. El grado 16, una variante del grado 7 con menor contenido en paladio, ofrece un comportamiento frente a la corrosi\u00f3n casi equivalente con una reducci\u00f3n significativa del coste, y merece m\u00e1s atenci\u00f3n de la que suele recibir. Esta gu\u00eda asocia cada grado a entornos \u00e1cidos espec\u00edficos, con umbrales de concentraci\u00f3n y temperatura que los ingenieros pueden tener en cuenta.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Por qu\u00e9 la decisi\u00f3n sobre las notas tiene m\u00e1s consecuencias de lo que crees<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">La resistencia a la corrosi\u00f3n del titanio se debe a una fina pel\u00edcula pasiva de di\u00f3xido de titanio (TiO\u2082) con capacidad de autorreparaci\u00f3n que se forma espont\u00e1neamente en presencia de ox\u00edgeno o humedad. En entornos oxidantes \u2014\u00e1cido n\u00edtrico, \u00e1cido cr\u00f3mico y la mayor\u00eda de los cloruros acuosos a temperatura ambiente\u2014, esta pel\u00edcula es estable y se regenera r\u00e1pidamente si se da\u00f1a. Por eso, el titanio sin alear cuenta con un historial de 40 a\u00f1os de servicio en los condensadores de las plantas de \u00e1cido n\u00edtrico.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">El problema radica en los entornos adversos. En \u00e1cido sulf\u00farico caliente, \u00e1cido clorh\u00eddrico caliente o cualquier entorno en el que se agote el ox\u00edgeno disuelto (pH bajo, alta temperatura, geometr\u00eda de hendiduras), esa pel\u00edcula pasiva no puede mantenerse. El titanio sin alear comienza a corroerse, a veces r\u00e1pidamente.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La estrategia de aleaci\u00f3n en los grados 7, 11, 16 y 17 aborda este problema directamente. Una peque\u00f1a adici\u00f3n de paladio (0,05\u20130,25%) reduce el potencial de corrosi\u00f3n del titanio hasta un valor en el que la pel\u00edcula pasiva se mantiene estable incluso en condiciones reductoras y desaireadas. El mecanismo es electroqu\u00edmico: el Pd act\u00faa como despolarizador cat\u00f3dico, desplazando el potencial de funcionamiento hacia la zona pasiva. Por eso, una adici\u00f3n de 0,21 TP3T de Pd transforma el comportamiento del grado 2 en HCl o H\u2082SO\u2084; no se trata de un peque\u00f1o ajuste en la formulaci\u00f3n, sino de una respuesta a la corrosi\u00f3n fundamentalmente diferente.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">El grado 12 adopta un enfoque diferente \u2014la incorporaci\u00f3n de molibdeno y n\u00edquel, que mejoran la estabilidad de la pel\u00edcula pasiva en salmueras cloradas calientes\u2014 sin necesidad de recurrir al costoso paladio.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Elegir un grado incorrecto, en cualquier sentido, conlleva un coste real.&nbsp;<strong>Especificar un grado 7 en exceso para una aplicaci\u00f3n con \u00e1cido n\u00edtrico puro \u2014que el grado 2 soporta perfectamente\u2014 multiplica por 2 o por 3 el coste del material sin aportar ning\u00fan beneficio t\u00e9cnico.<\/strong>&nbsp;Si no se especifica adecuadamente el grado 2 en un intercambiador de calor de H\u2082SO\u2084 del tipo 20%, se produce un fallo por corrosi\u00f3n en un plazo de entre 12 y 18 meses. La decisi\u00f3n no resulta complicada una vez que se ha caracterizado adecuadamente el entorno corrosivo.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Los cinco grados que realmente importan en el sector qu\u00edmico<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">M\u00e1s de 95% de titanio utilizado en procesos qu\u00edmicos industriales se clasifica en cinco grados. Los grados 1, 3, 4 y 5 tienen cada uno sus aplicaciones, pero los grados 1 y 3 han sido sustituidos en gran medida por el grado 2 para aplicaciones qu\u00edmicas; el grado 4 aporta resistencia sin ofrecer ventajas frente a la corrosi\u00f3n, y el grado 5 (Ti-6Al-4V) es una aleaci\u00f3n aeroespacial que, de hecho, tiene&nbsp;<em>peor<\/em>&nbsp;resistencia a la corrosi\u00f3n superior a la de los grados de protecci\u00f3n cat\u00f3dica (CP) en la mayor\u00eda de los entornos qu\u00edmicos.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Grado<\/th><th>Denominaci\u00f3n<\/th><th>Composici\u00f3n<\/th><th>Nivel de coste<\/th><th>Uso qu\u00edmico principal<\/th><\/tr><\/thead><tbody><tr><td>Grado 2<\/td><td>CP-Ti, ASTM R50400<\/td><td>99%+ Ti<\/td><td>Valor de referencia<\/td><td>\u00c1cidos oxidantes, \u00e1cido n\u00edtrico, \u00e1cidos reductores diluidos a temperatura ambiente<\/td><\/tr><tr><td>7\u00ba curso<\/td><td>Ti-0,2Pd, ASTM R52400<\/td><td>Grado 2 + 0,12\u20130,251 TP3T Pd<\/td><td>2\u20133 \u00d7 2.\u00ba curso<\/td><td>\u00c1cidos reductores: HCl, H\u2082SO\u2084, \u00e1cido fosf\u00f3rico, \u00e1cidos org\u00e1nicos<\/td><\/tr><tr><td>11.\u00ba curso<\/td><td>Ti-0,2Pd, ASTM R52250<\/td><td>Grado 1 + 0,12\u20130,251 TP3T Pd<\/td><td>Similar al 7.\u00ba curso<\/td><td>Igual que el grado 7, mayor capacidad de conformado (componentes de pared delgada)<\/td><\/tr><tr><td>Grado 12<\/td><td>Ti-Mo-Ni, ASTM R53400<\/td><td>Ti + 0,31 TP3T Mo + 0,81 TP3T Ni<\/td><td>~1,3\u20131,5 veces el de 2.\u00ba curso<\/td><td>Salmueras calientes de cloruro, agua de mar, entornos \u00e1cidos mixtos<\/td><\/tr><tr><td>16.\u00ba curso<\/td><td>Ti-0,05Pd, ASTM R52402<\/td><td>Grado 2 + 0,04\u20130,081 TP3T Pd<\/td><td>~1,5\u20132 veces el nivel 2<\/td><td>Casi equivalente al grado 7 con un menor coste de Pd<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Normas aplicables a las formas de los productos: chapa\/banda\/placa (ASTM B265), tubos sin costura y soldados para aplicaciones en entornos corrosivos (ASTM B337), tubos soldados para intercambiadores de calor (ASTM B338), tubos sin costura (ASTM B861), tubos soldados (ASTM B862), piezas forjadas (ASTM B381).<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Grado 2 \u2014 El punto de referencia para los entornos \u00e1cidos oxidantes<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>El grado 2 es la opci\u00f3n predeterminada adecuada para aplicaciones con \u00e1cidos oxidantes; sin embargo, no es la opci\u00f3n adecuada si existen condiciones reductoras.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">En la pr\u00e1ctica, los alumnos de 2.\u00ba curso obtienen unos resultados excepcionales en:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u00c1cido n\u00edtrico (HNO\u2083):<\/strong>\u00a0Resistente en todo el rango de concentraciones comerciales (10\u201365%) y a temperaturas de hasta el punto de ebullici\u00f3n. Su rendimiento es superior al de la mayor\u00eda de las aleaciones de n\u00edquel en corrientes de \u00e1cido n\u00edtrico contaminadas que contienen fluoruros, los cuales aceleran la corrosi\u00f3n en los aceros inoxidables, pero no en el titanio.<\/li>\n\n\n\n<li><strong>\u00c1cido cr\u00f3mico:<\/strong>\u00a0Resistente en todas las concentraciones a temperatura ambiente.<\/li>\n\n\n\n<li><strong>Cloro l\u00edquido e hipoclorito:<\/strong>\u00a0Estable hasta 2% Cl\u2082 en condiciones ambientales; se utiliza ampliamente en plantas de cloro-\u00e1lcali para \u00e1nodos, tuber\u00edas y equipos de manipulaci\u00f3n.<\/li>\n\n\n\n<li><strong>\u00c1cido sulf\u00farico y clorh\u00eddrico diluidos a temperatura ambiente:<\/strong>\u00a0El grado 2 tolera los \u00e1cidos reductores diluidos siempre que la temperatura sea baja y haya ox\u00edgeno disuelto. L\u00edmites pr\u00e1cticos: H\u2082SO\u2084 hasta ~5% a 25 \u00b0C; HCl hasta ~1\u20132% a 25 \u00b0C con ox\u00edgeno disuelto.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>En qu\u00e9 falla el 2.\u00ba curso:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>H\u2082SO\u2084 con una concentraci\u00f3n superior a 5% o a una temperatura superior a 60 \u00b0C<\/li>\n\n\n\n<li>HCl por encima de ~5\u20137% a temperatura ambiente en condiciones de aireaci\u00f3n, o por encima de ~1\u20132% a temperaturas elevadas o cuando se agota el ox\u00edgeno<\/li>\n\n\n\n<li>\u00c1cido fosf\u00f3rico caliente a m\u00e1s de 60 \u00b0C en concentraciones superiores a 10%<\/li>\n\n\n\n<li>Any crevice geometry in hot chloride solutions above 80\u00b0C<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The 80\u00b0C crevice corrosion threshold is important for equipment design. In heat exchanger tube-to-tubesheet joints, flange face contact areas, or gasketed connections, crevice geometries are unavoidable. At temperatures above 80\u00b0C in chloride media, Grade 2 can experience localized crevice attack even in environments where it shows no general corrosion.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Grade 7 \u2014 The Premier Choice for Reducing Acid Environments<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Grade 7 is the most corrosion-resistant commercially available titanium alloy, and the correct specification when reducing acids, elevated temperatures, or crevice risk are present.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The palladium content (0.12\u20130.25% by weight) shifts titanium\u2019s corrosion potential by approximately +200 mV vs the unalloyed material. This shift is enough to place the operating potential within the passive region in deaerated, reducing acid environments where Grade 2 would be active and corroding.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Practical performance data:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Hydrochloric acid (HCl):<\/strong>\u00a0Grade 7 resists corrosion up to approximately 20\u201327% concentration at 25\u00b0C (iso-corrosion curves from TIMET mill data). Grade 2 in aerated HCl handles up to ~5\u20137% at room temperature, but that limit drops sharply at elevated temperatures or when dissolved oxygen is depleted.<\/li>\n\n\n\n<li><strong>Sulfuric acid (H\u2082SO\u2084):<\/strong>\u00a0Resistant up to ~45% at 25\u00b0C, ~20% at 60\u00b0C, ~7% at boiling. Unalloyed Grade 2 begins to corrode above ~5% at room temperature.<\/li>\n\n\n\n<li><strong>Phosphoric acid (H\u2083PO\u2084):<\/strong>\u00a0Grade 7 handles concentrations up to ~80% at room temperature; Grade 2 is limited to ~30% at 25\u00b0C, and significantly less at elevated temperatures.<\/li>\n\n\n\n<li><strong>Organic acids (acetic, formic, oxalic):<\/strong>\u00a0Grade 7 is essentially inert across the full range of commercial concentrations at temperatures up to 100\u00b0C.<\/li>\n\n\n\n<li><strong>Crevice corrosion threshold:<\/strong>\u00a0Grade 7 does not suffer crevice corrosion in chloride solutions at temperatures below 250\u00b0C (at pH above 1). Grade 2\u2019s threshold is 80\u00b0C. This difference alone justifies Grade 7 for hot brine heat exchangers where crevice geometry cannot be eliminated.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Grade 7 also offers resistance to wet HCl gas and mixed acid systems common in pharmaceutical manufacturing \u2014 environments where neither stainless steel nor nickel alloys perform adequately without cost-prohibitive alloy selection.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The two environments where Grade 7 still fails:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Hydrofluoric acid (HF):<\/strong>\u00a0All titanium grades are attacked by HF. The fluoride ion dissolves the TiO\u2082 passive film. No titanium grade is suitable for HF service \u2014 use zirconium, PTFE-lined equipment, or Hastelloy C-276.<\/li>\n\n\n\n<li><strong>Fuming nitric acid (red fuming HNO\u2083 with >5% NO\u2082):<\/strong>\u00a0Can cause stress corrosion cracking in titanium. This is a specific exception to titanium\u2019s generally outstanding nitric acid resistance.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Grade 12 \u2014 The Cost-Efficient Workhorse for Chloride and Hot Brine Service<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Grade 12\u2019s molybdenum and nickel additions give it resistance in hot chloride environments that Grade 2 can\u2019t match \u2014 at roughly half the premium of Grade 7.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Grade 12 (Ti-0.3Mo-0.8Ni) doesn\u2019t use palladium, which eliminates the largest cost driver in Grade 7 pricing. Instead, Mo and Ni stabilize the passive film specifically in hot brine, seawater, and mixed chloride-acid environments.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Compared to Grade 2:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Crevice corrosion resistance in seawater extends to approximately 120\u00b0C (vs. 80\u00b0C for Grade 2)<\/li>\n\n\n\n<li>Better resistance to hot phosphoric acid containing halide impurities<\/li>\n\n\n\n<li>Improved tensile strength (approximately 483 MPa minimum vs. 345 MPa minimum for Grade 2) \u2014 allows thinner wall construction<\/li>\n\n\n\n<li>Better resistance in hot sodium hypochlorite solutions<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Compared to Grade 7:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Grade 12 is generally inferior in straight reducing acid service (HCl, H\u2082SO\u2084)<\/li>\n\n\n\n<li>Grade 12 performs comparably or better in hot chloride brines and seawater systems where the primary concern is crevice attack, not reducing acid corrosion<\/li>\n\n\n\n<li>Grade 12 has no advantage in HF environments (both fail)<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Best-fit scenarios for Grade 12:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Offshore desalination and produced water handling (hot saline, elevated temperature)<\/li>\n\n\n\n<li>Pulp and paper bleach plant equipment exposed to chloride\/hypochlorite mixtures<\/li>\n\n\n\n<li>Marine chemical processing where seawater cooling is combined with mild acid exposure<\/li>\n\n\n\n<li>Refineries with brine recirculation systems where straight acid resistance isn\u2019t needed<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Grade 16 \u2014 The Underdiscussed Alternative to Grade 7<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Grade 16 contains roughly half the palladium of Grade 7 (0.04\u20130.08% vs. 0.12\u20130.25%) and delivers corrosion resistance that is, in most practical chemical environments, indistinguishable from Grade 7.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This grade receives almost no attention in standard engineering guidance despite a straightforward value proposition: palladium consistently accounts for a significant fraction of the cost premium in Grade 7 and Grade 11 plate and tubing. At Pd market prices, a plate order in Grade 16 can cost 20\u201335% less than an equivalent Grade 7 order with comparable corrosion performance in the majority of process environments.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The corrosion mechanism is the same \u2014 Pd addition shifts the corrosion potential into the passive region \u2014 and test data from TIMET and the Corrosion Engineering literature shows that 0.05% Pd is sufficient to achieve passive behavior in most reducing acid environments. The advantage of higher Pd content (Grade 7) appears primarily at the extremes: very concentrated reducing acids, very high temperatures, or environments where the corrosion potential is driven particularly low.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>When to specify Grade 16 over Grade 7:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Service environments within the moderate range (H\u2082SO\u2084 &lt;20%, HCl &lt;5%, temperatures below 80\u00b0C)<\/li>\n\n\n\n<li>Applications where cost pressure is significant and the engineer can document equivalency from published test data<\/li>\n\n\n\n<li>Projects requiring large plate quantities where the cost delta is material (fabrication of reactor shells, large heat exchanger shells)<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>When to stick with Grade 7:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Hot concentrated reducing acid service near the upper limits of Grade 7\u2019s corrosion resistance<\/li>\n\n\n\n<li>Applications where conservative specification is contractually required (nuclear, pharmaceutical process equipment with FDA validation)<\/li>\n\n\n\n<li>Crevice environments above 200\u00b0C \u2014 the higher Pd content provides more conservatism<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Grade 17 is the Grade 1-based equivalent of Grade 16 (more ductile, lower strength) and follows the same logic for applications requiring extreme formability with reducing acid resistance.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Acid-by-Acid Selection Framework<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The most direct way to use this information is an acid-environment matrix. The table below reflects commonly referenced data from TIMET corrosion manuals and published corrosion engineering literature.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Titanium Grade Selection by Acid Environment<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image\"><img fetchpriority=\"high\" decoding=\"async\" width=\"2496\" height=\"1664\" src=\"https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix.webp\" alt=\"Titanium grade acid selection matrix by acid type \u2014 color-coded recommendation chart showing Grade 2, Grade 7, and Grade 16 suitability for nitric, sulfuric, hydrochloric, and phosphoric acid environments\" class=\"wp-image-4390\" title=\"\" srcset=\"https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix.webp 2496w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix-300x200.webp 300w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix-1024x683.webp 1024w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix-768x512.webp 768w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix-1536x1024.webp 1536w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix-2048x1365.webp 2048w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix-18x12.webp 18w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-grade-acid-selection-matrix-600x400.webp 600w\" sizes=\"(max-width: 2496px) 100vw, 2496px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\u00c1cido<\/th><th>Concentraci\u00f3n<\/th><th>Temperatura<\/th><th>Grado recomendado<\/th><th>Notas<\/th><\/tr><\/thead><tbody><tr><td>Nitric acid (HNO\u2083)<\/td><td>10\u201365%<\/td><td>Up to boiling<\/td><td><strong>Grado 2<\/strong><\/td><td>All CP grades adequate; Grade 7 offers no advantage<\/td><\/tr><tr><td>Nitric acid (red fuming)<\/td><td>&gt;5% NO\u2082<\/td><td>Any<\/td><td>Avoid all Ti<\/td><td>SCC risk in all grades<\/td><\/tr><tr><td>Sulfuric acid (H\u2082SO\u2084)<\/td><td>&lt;5%<\/td><td>&lt;60\u00b0C<\/td><td>Grado 2<\/td><td>Dissolved O\u2082 must be present<\/td><\/tr><tr><td>Sulfuric acid<\/td><td>5\u201345%<\/td><td>&lt;60\u00b0C<\/td><td><strong>Grade 7 or Grade 16<\/strong><\/td><td>Grade 2 corrodes above 5%<\/td><\/tr><tr><td>Sulfuric acid<\/td><td>&gt;45%<\/td><td>Any<\/td><td>Grade 7 (with caution)<\/td><td>Test data required; consider Zr or Ta above 60%<\/td><\/tr><tr><td>Hydrochloric acid (HCl)<\/td><td>&lt;5\u20137%, aerated<\/td><td>RT only<\/td><td>Grado 2<\/td><td>Dissolved O\u2082 required; limit drops sharply at elevated T<\/td><\/tr><tr><td>Hydrochloric acid<\/td><td>5\u201327%<\/td><td>Up to 50\u00b0C<\/td><td><strong>Grade 7 or Grade 16<\/strong><\/td><td>Grade 2 not adequate above ~5\u20137% aerated<\/td><\/tr><tr><td>Hydrochloric acid<\/td><td>&gt;27%<\/td><td>Any<\/td><td>Consult test data<\/td><td>Grade 7 may corrode above 27% at elevated T<\/td><\/tr><tr><td>Phosphoric acid (H\u2083PO\u2084)<\/td><td>&lt;30%<\/td><td>&lt;80\u00b0C<\/td><td>Grado 2<\/td><td>Acceptable with aeration<\/td><\/tr><tr><td>Phosphoric acid<\/td><td>30\u201380%<\/td><td>Any<\/td><td><strong>Grade 7 or Grade 16<\/strong><\/td><td>Grade 12 acceptable if halide-free<\/td><\/tr><tr><td>Hydrofluoric acid (HF)<\/td><td>Any<\/td><td>Any<\/td><td>Ninguno<\/td><td>All Ti grades fail \u2014 use Zr, PTFE-lined, or Hastelloy<\/td><\/tr><tr><td>Organic acids (acetic, formic)<\/td><td>All commercial<\/td><td>&lt;100\u00b0C<\/td><td>Grade 2 or Grade 7<\/td><td>Grade 2 in dilute, Grade 7 for concentrated\/hot<\/td><\/tr><tr><td>Hot chloride brine<\/td><td>NaCl &gt;10%, &gt;80\u00b0C<\/td><td>80\u2013150\u00b0C<\/td><td><strong>Grade 12 or Grade 7<\/strong><\/td><td>Grade 2 crevice risk above 80\u00b0C<\/td><\/tr><tr><td>Hot hypochlorite<\/td><td>NaOCl &gt;1%, &gt;60\u00b0C<\/td><td>Up to boiling<\/td><td>Grade 12 or Grade 7<\/td><td>Grade 2 marginal above 60\u00b0C<\/td><\/tr><tr><td>Wet Cl\u2082 gas<\/td><td>Up to 2%<\/td><td>&lt;100\u00b0C<\/td><td>Grado 2<\/td><td>All CP grades adequate in wet Cl\u2082<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">This framework covers the most common acid environments in chemical processing. Mixed acid systems, contaminated streams (e.g., HNO\u2083 + HF in stainless steel pickling), and proprietary process fluids require individual corrosion testing \u2014 no published table fully substitutes for immersion testing in the actual process fluid.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">The Palladium Premium: When Grade 7 Cost Is Hard to Justify<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Palladium trades at roughly $1,000\u2013$1,500 per troy ounce. Grade 7 contains 0.12\u20130.25% Pd by weight \u2014 in a 1,000 lb plate order, that\u2019s approximately 1.2\u20132.5 lbs of palladium embedded in the alloy. That Pd content adds a material premium that is directly tied to palladium spot pricing.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">When a Grade 2 plate runs $5\u20138\/lb and Grade 7 runs $12\u201318\/lb, the cost decision deserves engineering rigor rather than defaulting to the higher grade out of caution.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A simple ROI framing:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Cost of premature Grade 2 failure:<\/strong>\u00a0Unplanned shutdown to replace a heat exchanger in a continuous-process chemical plant can cost $200,000\u2013$500,000 in lost production, plus $50,000\u2013$150,000 in replacement materials and labor.<\/li>\n\n\n\n<li><strong>Cost of upgrading to Grade 7:<\/strong>\u00a0On a 10,000 lb heat exchanger bundle, the Grade 7 premium over Grade 2 might be $70,000\u2013$100,000.<\/li>\n\n\n\n<li><strong>Break-even:<\/strong>\u00a0If Grade 7 extends service life by even 2\u20133 years in a reducing acid environment where Grade 2 would fail in 1\u20132 years, the economics strongly favor Grade 7.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Grade 16 changes this math further. If Grade 16 pricing comes in at $8\u201312\/lb \u2014 which reflects the lower Pd content \u2014 and it delivers equivalent service life in that specific environment, the premium over Grade 2 drops to a range where even modest reliability improvement justifies the upgrade.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The practical recommendation:&nbsp;<strong>default to Grade 2 for verified oxidizing-only environments, Grade 16 for moderate reducing acid service where cost matters, and Grade 7 for aggressive reducing acid environments or where crevice corrosion at elevated temperature is a known risk.<\/strong><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Fabrication and Welding: Where Grade Selection Gets Invalidated<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Titanium\u2019s corrosion resistance can be destroyed by poor welding practice regardless of grade specified. This point is underemphasized in most grade selection guides.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>The critical issue: alpha-case formation.<\/strong>&nbsp;When titanium is welded or heated above 600\u00b0C in the presence of air, nitrogen, or oxygen, a hard, brittle, oxygen-rich surface layer called alpha-case forms. Alpha-case has poor ductility and, critically, degraded corrosion resistance because its chemistry no longer matches the base alloy.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For chemical service welding:<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" width=\"1024\" height=\"1024\" src=\"https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-weld-color-guide.webp\" alt=\"Titanium weld bead color quality guide \u2014 silver-white PASS, straw yellow ACCEPTABLE, dark gold CAUTION, blue-purple REJECT, grey oxide REJECT \u2014 field inspection reference for argon shielding verification\" class=\"wp-image-4389\" title=\"\" srcset=\"https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-weld-color-guide.webp 1024w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-weld-color-guide-300x300.webp 300w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-weld-color-guide-150x150.webp 150w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-weld-color-guide-768x768.webp 768w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-weld-color-guide-12x12.webp 12w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-weld-color-guide-600x600.webp 600w, https:\/\/hontitan.com\/wp-content\/uploads\/2026\/07\/titanium-weld-color-guide-100x100.webp 100w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Inert gas shielding is mandatory \u2014 on both weld face and weld root.<\/strong>\u00a0Back-purging with argon (minimum 99.995% purity) is not optional in titanium welding for chemical service. A \u201ccolor check\u201d of the weld bead is the practical quality indicator: silver-white is acceptable, straw-yellow is borderline acceptable, blue or purple means oxygen contamination and the weld must be rejected.<\/li>\n\n\n\n<li><strong>Titanium must be welded with titanium filler wire<\/strong>\u00a0of the same or lower grade. Do not use Grade 5 filler (Ti-6Al-4V) for Grade 2 or Grade 7 base metal \u2014 the filler\u2019s aluminum content degrades corrosion resistance in the weld zone.<\/li>\n\n\n\n<li><strong>Surface cleanliness:<\/strong>\u00a0Titanium reacts with iron at weld temperatures. Iron contamination from grinding with steel tools, contact with steel wire brushes, or iron particles in the shop environment can cause localized corrosion at welds. Dedicated stainless steel brushes and clean work areas are required.<\/li>\n\n\n\n<li><strong>Post-weld passivation:<\/strong>\u00a0Titanium typically doesn\u2019t require chemical passivation (unlike stainless steel), but mechanical removal of any discolored weld zones followed by solvent cleaning is good practice before placing equipment into service.<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">Grade 7 and Grade 12 weld in essentially the same way as Grade 2 \u2014 no special parameters beyond the standard titanium welding requirements above. The corrosion resistance at welds matches the base metal when done correctly.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Summary: Matching Grade to Environment<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Titanium grade selection for chemical processing reduces to a small number of decisions:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Is the acid environment primarily oxidizing?<\/strong>&nbsp;\u2192 Grade 2 is the standard specification. It delivers 40+ year service life in nitric acid, chromic acid, and wet chlorine service at a competitive cost.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Are reducing acids present (HCl, H\u2082SO\u2084, hot phosphoric)?<\/strong>&nbsp;\u2192 Specify Grade 7 or Grade 16. The palladium addition is not a luxury in these environments \u2014 it is what makes titanium viable at all. Grade 16 is the cost-conscious choice for service within moderate concentration and temperature limits.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Is hot chloride brine or seawater the primary concern, not reducing acids?<\/strong>&nbsp;\u2192 Grade 12 is the fit. The Mo-Ni addition addresses the specific crevice corrosion mechanism in hot saline environments at a lower cost than Pd-bearing grades.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Is hydrofluoric acid involved?<\/strong>&nbsp;\u2192 No titanium grade works. Stop the evaluation and consider zirconium, PTFE-lined construction, or Hastelloy C-276.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The grade selection itself is only half the engineering decision. Weld quality, joint design to minimize crevice geometry, and process stream characterization (particularly dissolved oxygen content, temperature profile, and contaminant ions) determine whether the specified grade performs as intended. A correctly specified Grade 2 with clean welds in a nitric acid environment will outlast poorly fabricated Grade 7 in the same environment every time.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Preguntas frecuentes<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>What is the most corrosion-resistant titanium grade for chemical service?<\/strong><br>Grade 7 (Ti-0.2Pd) is the most corrosion-resistant commercially available titanium alloy. Its palladium addition shifts the corrosion potential into the passive region in reducing acid environments where unalloyed titanium corrodes. It resists HCl up to ~10% and H\u2082SO\u2084 up to ~30% at ambient temperature, and does not suffer crevice corrosion in chloride solutions below 250\u00b0C at pH above 1.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>When should I use Grade 12 instead of Grade 7?<\/strong><br>Grade 12 is the preferred choice when the primary corrosion risk is hot chloride brine or seawater exposure \u2014 not reducing acids. Its Mo-Ni addition provides superior crevice corrosion resistance in hot saline environments compared to Grade 2, at lower cost than Grade 7. If your process involves hot H\u2082SO\u2084 or HCl, Grade 7 outperforms Grade 12.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>What is the difference between Grade 7 and Grade 16?<\/strong><br>Both grades use palladium additions to improve reducing acid corrosion resistance. Grade 7 contains 0.12\u20130.25% Pd; Grade 16 contains 0.04\u20130.08% Pd. Grade 16\u2019s lower Pd content makes it less expensive, and in most practical chemical processing environments within moderate acid concentrations and temperatures, its corrosion performance is equivalent to Grade 7. Grade 7 provides more conservatism at extreme conditions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Does titanium corrode in hydrofluoric acid?<\/strong><br>Yes. All titanium grades are attacked by hydrofluoric acid (HF) and fluoride-containing solutions at pH below approximately 3. Fluoride ions dissolve the protective TiO\u2082 passive film. No titanium grade should be specified for HF service \u2014 use zirconium, fluoropolymer (PTFE\/PFA) lined equipment, or nickel alloys such as Hastelloy C-276.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Is Grade 2 titanium acceptable for sulfuric acid service?<\/strong><br>Grade 2 is acceptable for dilute sulfuric acid (less than 5% H\u2082SO\u2084) at ambient temperature when dissolved oxygen is present. Above 5% concentration, above 60\u00b0C, or in deaerated conditions, Grade 2 corrodes at unacceptable rates. Grade 7 or Grade 16 should be specified for any H\u2082SO\u2084 service above these thresholds.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Why does weld quality matter so much in titanium chemical equipment?<\/strong><br>Titanium welded without adequate inert gas back-purging develops an oxygen-contaminated surface layer (alpha-case) that has degraded corrosion resistance and poor ductility. A visually perfect weld with blue or purple discoloration is a failed weld in chemical service. Titanium welding requires argon back-purging, dedicated tools free of iron contamination, and weld color inspection as a mandatory quality check.<\/p>","protected":false},"excerpt":{"rendered":"<p>Not all titanium performs equally in chemical service. Grade 2 handles oxidizing environments like nitric acid reliably, but it fails in reducing acids such as hydrochloric and sulfuric above ~5% concentration. Grade 7 \u2014 Grade 2 with a palladium addition \u2014 extends resistance into reducing acid environments up to ~10% HCl and ~30% H2SO4 at [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-4388","post","type-post","status-publish","format-standard","hentry","category-blog"],"_links":{"self":[{"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/posts\/4388","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/comments?post=4388"}],"version-history":[{"count":1,"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/posts\/4388\/revisions"}],"predecessor-version":[{"id":4391,"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/posts\/4388\/revisions\/4391"}],"wp:attachment":[{"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/media?parent=4388"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/categories?post=4388"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/hontitan.com\/es\/wp-json\/wp\/v2\/tags?post=4388"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}