A higher number is not a higher strength class
Grade 7 should not be read as a general strengthening step beyond titanium Grade 2. Palladium is considered for improved corrosion behaviour in certain demanding process environments. The decision therefore starts with the fluid and exposure conditions. Mechanical requirements remain important, but similar strength ranges do not explain the corrosion rationale. Failure of a Grade 2 component alone does not establish Grade 7 as a certain solution. Examining damage location, morphology and operating changes helps separate material, design and maintenance effects.
The fluid’s name alone is insufficient
Describing a process liquid by its main chemical name can hide important details. Concentration, temperature, pH, water content and additional constituents affect titanium surface behaviour. Cleaning, initial commissioning and shutdown can differ from normal operation. Evaporation and deposits can create conditions at the component surface unlike the tank average. Earlier analyses, current samples and service history therefore have value together. A room-temperature compatibility table cannot establish performance in a hot, variable process. How the environment changes over time is also an input to material selection.
A crevice creates a local environment
Surfaces beneath gaskets, within threaded connections or overlaps, or under deposits can behave differently from freely exposed areas. Changes in local chemistry can cause confined damage even when the general surface looks sound. Showing where these geometries occur is more informative for Grade 7 assessment than stating total chloride content alone. Design considerations can include drainage, cleaning access and deposit control. A project may need both material change and design improvement; neither automatically replaces the other. Marking damage locations on photographs of the existing component provides a concrete starting point for technical discussion.
Damage concentrated beneath a gasket is a different observation from damage spread across the freely exposed surface. Recording this distribution helps distinguish local geometry effects from general exposure. Assembly orientation and locations where liquid remains during shutdown can be marked on the same drawing, connecting operating data with physical geometry.
Assess the surface left by fabrication
Corrosion assessment does not end at the base material’s chemical analysis. Weld cleanliness, shielding, residual contamination and processing marks belong in the finished-component review. A tube weld root and a freely exposed plate surface may have different manufacturing histories. Tools and cleaning agents used during maintenance matter too. A Grade 2 versus Grade 7 comparison is meaningful under comparable surface and fabrication conditions. Repeating unsuccessful fabrication details from the old part can limit the expected benefit of a grade change. Define the welding procedure and final surface requirements in advance.
Prepare a process request that supports comparison
Identify Grade 2 as UNS R50400 and Grade 7 as UNS R52400. Define the product and dimensional requirements separately for tube, plate or flange; a bar standard does not establish flange pressure class. Providing the information below together clarifies which technical questions need answers. Mark uncertain operating data separately instead of guessing. For critical service, complete selection with project design conditions and the necessary specialist assessment. The aim is to match material with the expected environment rather than merely buy a more alloyed product; documentation scope forms part of that choice.
- Normal, cleaning and shutdown conditions; chemical analysis and temperature range.
- Crevice and connection geometry; damage history of the existing component.