Titanium Pipe Fittings: Effects Of High Hydrogen Content & Key Precautions

Titanium is highly chemically active and prone to hydrogen absorption during processing, heat treatment, welding, pickling and other procedures. Excessive hydrogen content can cause hydrogen embrittlement, hydrogen-induced cracking and performance degradation, severely compromising the service safety of  titanium pipe fittings.

 

 

1.1 Existing Forms of Hydrogen

Hydrogen atoms dissolve interstitially in the crystal lattices of α-Ti or β-Ti, with very low solubility at low temperatures.

When hydrogen content exceeds the solid solubility limit or the temperature drops, brittle phases such as TiH₂ and TiH₁₋₂ are formed, precipitating in acicular, flaky or massive shapes, and usually distributed at grain boundaries, dislocations and stress concentration areas.

 

1.2 Judgment Criteria for Excessive Hydrogen Content

National standards, ASTM B338 and other specifications stipulate that hydrogen content in titanium and titanium alloy pipe fittings shall be ≤ 0.015% (150 ppm).

100 ppm: Impact toughness decreases significantly.

300–500 ppm: Plasticity deteriorates sharply with massive hydride precipitation.

0.05%: The material becomes extremely brittle and prone to sudden brittle fracture without warning at room temperature.

 

2.1 Hydrogen Embrittlement

The high-hardness acicular TiH₂ is incompatible with the matrix properties, easily leading to microcracks.

Stress drives hydrogen to accumulate in high-stress zones, accelerating hydride precipitation and propagation into intergranular cracks.

Fracture is delayed and prone to sudden brittle fracture in service with strong concealment.

 

2.2 Sharp Deterioration of Mechanical Properties

Toughness drops substantially, and brittleness becomes more pronounced at low temperatures.

Plasticity deteriorates, making bending, flattening and other processing operations liable to cracking.

Hydrides act as fatigue sources, significantly reducing fatigue life.

 

2.3 High Incidence of Welding Defects

Hydrogen in the molten pool fails to escape in time upon cooling, forming hydrogen pores.

Hydrides generate cold cracks under welding stress.

Toughness of welds and heat-affected zones decreases, resulting in uneven joint performance.

 

2.4 Deterioration of Corrosion Resistance

Surface hydrides tend to spall, accelerating corrosion.

Hydrogen embrittlement cracks act as medium channels, easily causing stress corrosion cracking.

Hydrogen absorption and corrosion promote each other at local defects, accelerating failure.

 

 

Hydrogen absorption of titanium accelerates above 400℃; massive hydrogen absorption occurs easily if the furnace contains water vapor, hydrogen or a reducing atmosphere.

 

Impure argon, high hydrogen content in base metal/welding wire, inadequate shielding, and moisture intrusion into the molten pool generate hydrogen.

Acid reacts with titanium to produce active hydrogen during pickling; excessive concentration, temperature and time will aggravate hydrogen absorption.

 

Damage to the surface oxide film and formation of fresh active surfaces become channels for hydrogen absorption.

Excessive hydrogen content in raw materials themselves, and moisture on the surface decomposes to produce hydrogen at high temperatures in humid environments.

 

4.1 Source Control

Select titanium tube blanks with hydrogen content ≤ 100 ppm as raw materials, conduct mandatory inspection upon factory arrival, and reject non-conforming materials.

 

Control workshop humidity ≤ 60%, keep workpieces dry, and prohibit processing with water or oil contamination.

Thoroughly remove oil, dirt and rust before welding, and avoid contamination caused by contact with ironware.

 

4.2 Process Control During Processing

Heat treatment

Prioritize vacuum or high-purity argon shielding annealing, with argon dew point < -40℃.

Recommended dehydrogenation temperature: 538–760℃; avoid oxidation above 760℃; prohibit reducing atmospheres and shorten heating time.

 

Welding

Use high-purity argon ≥ 99.99%, with dew point < -40℃.

Clean and dry grooves before welding, adopt low current and high welding speed, and provide full shielding on both front and back sides until cooling below 200℃.

Adopt low-hydrogen matching welding wires.

 

Pickling

Adopt low-concentration HF + HNO₃ system, temperature ≤ 40℃, duration 1–3 minutes.

Fully rinse and dry after pickling; prohibit pickling with single acid such as hydrochloric acid or sulfuric acid.

 

Mechanical processing

Use special cutting tools and compatible cutting fluids to avoid frictional temperature rise.

Reduce tool marks and excessive grinding to protect the oxide film.

 

4.3 Remedial Measure for Excessive Hydrogen: Vacuum Dehydrogenation Annealing

Conduct vacuum dehydrogenation when hydrogen content > 150 ppm:

Temperature: 580–650℃

Vacuum degree: ≤ 0.066 Pa

Holding time: 2–4 hours

Cool in furnace to below 200℃ before discharging

 

4.4 Quality Inspection

Detect hydrogen content by inert gas fusion-thermal conductivity method to ensure ≤ 150 ppm.

Inspect mechanical properties such as impact toughness, elongation and flattening performance.

Perform UT and PT non-destructive testing on key parts to detect hydrogen-induced cracks.

 

 

Ruihang provides high-quality titanium and titanium alloy products. Our stringent manufacturing processes ensure that we fully meet our customers' requirements.For more details, please feel free to contact us by email: Sam.Rui@bjrh-titanium.com