Quality Inspection Methods for Titanium Alloy Forgings

The presence of defects in TC4 titanium forgings can affect the quality of subsequent processing or machining, while others can severely impact the performance and use of titanium forgings and titanium alloy forgings, even significantly reducing the service life of finished parts and endangering safety. Therefore, to improve the quality of titanium forgings, in addition to strengthening quality control in the process and taking corresponding measures to eliminate defects, necessary quality inspections should be conducted to prevent titanium forgings with defects that adversely affect subsequent processes (such as heat treatment, surface treatment, and cold working) and performance from entering later stages. After quality inspection, remedial measures can be taken for the manufactured titanium forgings based on the nature of the defects and their impact on use, ensuring they meet technical standards or usage requirements. titanium 6al4v foil / titanium forged block / Gr23 Ti-6Al-4V ELI Titanium Sheet

Therefore, titanium forging quality inspection, in a sense, serves two purposes: firstly, it controls the quality of manufactured titanium forgings; secondly, it provides direction for improving the forging process, ensuring that the quality of titanium forgings meets the requirements of titanium forging technical standards and satisfies design, processing, and usage requirements. The inspection of titanium forging quality includes both appearance and internal quality inspection. Visual quality inspection mainly refers to the inspection of the geometric dimensions, shape, and surface condition of titanium forgings; internal quality inspection mainly refers to the inspection of the chemical composition, macrostructure, microstructure, and mechanical properties of titanium forgings.

Specifically, visual quality inspection of titanium forgings involves checking whether the shape and geometric dimensions of the titanium forgings conform to the specifications in the drawings, and whether there are defects on the surface of the titanium forgings, what kind of defects they are, and what their morphological characteristics are. Surface condition inspection generally involves checking for defects such as surface cracks, folds, wrinkles, dents, orange peel, blistering, blemishes, corrosion pits, dents, foreign matter, incomplete filling, pits, missing material, and scratches. Internal quality inspection, on the other hand, examines the inherent quality of the titanium forgings themselves, addressing quality conditions that cannot be detected by visual quality inspection. It includes checking for internal defects and mechanical properties of the titanium forgings, and for important, critical, or large titanium forgings, chemical composition analysis should also be performed. For internal defects, we will use low-magnification inspection, fracture surface inspection, and high-magnification inspection to check for defects in titanium forgings such as internal cracks, shrinkage cavities, porosity, coarse grains, white spots, dendritic crystals, flow lines not conforming to the shape, disordered flow lines, flow penetration, coarse grain rings, oxide films, delamination, overheating, and burnt structures. For mechanical properties, we mainly check room temperature tensile strength, plasticity, toughness, hardness, fatigue strength, high-temperature instantaneous fracture strength, high-temperature creep strength, creep ductility, and high-temperature creep strength.

Because titanium forgings are subjected to different stresses, importance, and working conditions during use, and the materials and metallurgical processes used also vary, different departments classify titanium forgings according to the above conditions and departmental requirements. Different departments and different standards will have different classifications of titanium forgings. However, the overall quality inspection of titanium forgings cannot be separated from two main categories of inspection: appearance quality inspection and internal quality inspection. The only difference is that the specific inspection items, quantities, and requirements differ depending on the category of the titanium forging.

Selection of Titanium Pipe Material and Wall Thickness Based on Media Corrosion

The corrosiveness of the medium directly determines the material grade and wall thickness design of the titanium pipe. Different corrosion levels require different titanium material properties to ensure that the corrosion rate is controlled within a safe range (typically ≤0.1mm per year).

(I) Weakly Corrosive Media: Industrial Pure Titanium Preferred, Controlling Economic Wall Thickness

Weakly corrosive media refer to neutral aqueous solutions (pH 6-8), room temperature air, or low-concentration non-oxidizing media (such as fresh water, lubricating oil, compressed air). In these scenarios, the requirements for the corrosion resistance of titanium materials are relatively low, and industrial pure titanium TA1 or TA2 can be selected. TA1 titanium pipes have good plasticity and processing performance, suitable for thin-walled pipes (wall thickness ≤2mm); TA2 titanium pipes have slightly higher strength than TA1 (tensile strength ≥450MPa), suitable for medium-walled pipes (2-5mm), and can have a service life of over 20 years in weakly corrosive environments. Grade 1 Titanium Tube / Titanium Alloy Seamless Rectangular Pipe / titanium heat exchanger pipe

Wall thickness design must consider medium flow velocity and pressure: For low-pressure (≤1MPa), low-flow-velocity (≤2m/s) scenarios (such as cooling water pipelines), the wall thickness should be designed to be 1.2 times the nominal pressure. For example, a 2mm wall thickness is sufficient for a DN50 pipe to meet strength requirements. If the flow velocity is higher (2-5m/s), the wall thickness needs to be increased by 10%-20% to resist erosion corrosion. For example, a 3mm wall thickness TA2 titanium pipe can be used for a DN100 circulating water pipeline to avoid wall thickness reduction caused by local turbulence.

(II) Moderately corrosive media: Select high-purity titanium or titanium alloys to enhance wall thickness redundancy.

Moderately corrosive media include weakly acidic solutions (pH 4-6), chloride ion-containing solutions (concentration ≤1000ppm), or low-temperature dilute nitric acid (≤50℃). In these scenarios, titanium materials need to have certain corrosion resistance and strength. Industrial pure titanium TA3 or titanium alloy TC4 are preferred. TA3 titanium pipes have lower impurity content than TA2, resulting in superior corrosion resistance, especially in water containing trace amounts of chloride ions. TC4 titanium alloy (titanium-aluminum-vanadium alloy) boasts high strength (tensile strength ≥895MPa) and corrosion resistance comparable to pure titanium, making it suitable for applications requiring a balance between strength and corrosion resistance (such as pressure pipelines).

Wall thickness design must allow for corrosion allowance: For weakly acidic media with a pH of 5-6 (such as food processing wastewater), a corrosion allowance of 0.5-1mm is recommended. For example, for a DN80 pipeline with a design pressure of 1.6MPa, a nominal wall thickness of 3mm + a corrosion allowance of 0.5mm would necessitate the use of 3.5mm wall thickness TA3 titanium pipes. In cooling circulating water containing chloride ions (concentration 500-1000ppm), the corrosion allowance needs to be increased to 1-1.5mm. DN150 pipelines can utilize 4mm wall thickness TA3 titanium pipes to ensure a service life of over 15 years.

(III) Strong Corrosion Media: Select Corrosion-Resistant Titanium Alloys, Increase Wall Thickness and Anti-Corrosion Coating

Strong corrosion media include strong acids (pH < 4), high concentrations of chloride ions (> 1000 ppm), oxidizing acids (such as nitric acid and chromic acid), or fluoride-containing media. In these scenarios, titanium materials must possess good resistance to localized corrosion. Titanium-palladium alloys TA9 and TA10, or nickel-titanium alloys, are preferred. TA9 titanium pipes contain 0.12%-0.25% palladium, improving corrosion resistance in hydrochloric acid and sulfuric acid; TA10 titanium pipes contain 0.2%-0.4% palladium, offering superior resistance to crevice corrosion and pitting corrosion, suitable for high-salt wastewater (chloride ion concentration > 5000 ppm); nickel-titanium alloys (such as Ti-6Al-4V-0.1Ru) can withstand strong oxidizing media such as boiling nitric acid.

The wall thickness design requires double protection: the basic wall thickness is calculated as 1.5 times the nominal pressure, and the corrosion allowance is 2-3mm. For example, for a DN65 pipeline (design pressure 2.5MPa) transporting 5% hydrochloric acid, TA9 titanium pipe is selected, with a nominal wall thickness of 5mm + a corrosion allowance of 2mm, resulting in an actual wall thickness of 7mm. At the same time, a polytetrafluoroethylene coating (thickness 0.2-0.5mm) or glass flake lining can be applied to the inner wall of the pipe to form a "titanium material + coating" dual anti-corrosion system, which is especially suitable for highly corrosive scenarios with strong turbulence (flow velocity > 5m/s) and reduces the risk of erosion corrosion.

A Brief Overview of Titanium Plate Density

Titanium plates, as an excellent engineering material, are widely used in many fields. Among its numerous physical and mechanical properties, density is an important indicator.

Titanium plates have a relatively low density, typically around 4.5 g/cm³. Compared to other common metallic materials, such as steel and aluminum, titanium plates have a significantly lower density. This low density characteristic gives it an advantage in lightweight design, helping to reduce structural weight and improve overall efficiency. Grade 5 Ti-6Al-4V Titanium Sheet / Grade 7 Ti-0.2Pd Titanium Sheet / Gr9 Ti-3Al-2.5V Titanium Sheet

The density of titanium plates is affected by several factors, the most important of which are the material and manufacturing process. Different materials and manufacturing processes can affect its crystal structure and atomic arrangement, thus affecting its density. Furthermore, the presence of impurities and internal defects can also have a specific impact on its density.