1. Factory Background: GR2 Titanium Tube in a Chlorate Plant Upgrade
2. Material Overview: Industrially Pure Titanium Grades GR1, GR2, and GR3
3. Welding Metallurgy of Titanium: Heat Input and Cooling Rate Effects
4. Standards and Requirements for Titanium Tube Welding
4.2 Welding Environment and Technique
5. Post Weld Quality Inspection and Qualification
5.1 Using the process parameters above, titanium tube welds were evaluated by
5.2 Performance Outcomes in Chemical Service
5.3 Best Practices Summary for Titanium Tube Welding in Chemical Plants
Summary of Strong Oxidant Production Equipment
In large-scale chemical production lines, materials selection for piping directly affects safety, uptime, and lifecycle costs. This article presents an application case of pure titanium tube welding and post-weld quality inspection in a chlorate production facility, and summarizes material characteristics, welding metallurgy, process controls, standards, and verification methods. Throughout, we highlight why the titanium tube—particularly GR2—delivers a compelling combination of corrosion resistance, mechanical reliability, and weldability for chemical media.
1. Factory Background: GR2 Titanium Tube in a Chlorate Plant Upgrade
Project: Phase II technical transformation and expansion of the Rongping Joint Chemical Plant for potassium chlorate (KClO3) production, annual capacity 20,000 tons.
Piping scope: Main process trunk lines constructed with GR2 pure titanium tube for enhanced corrosion resistance.
Dimensional range: Diameters from 18 mm to 133 mm; maximum wall thickness 3 mm; total pipe length about 300 m.
Using GR2 titanium tube in this corrosive service significantly increases service life versus stainless steels, reduces unplanned shutdowns, and lowers total cost of ownership through minimized corrosion-induced failures.
2. Material Overview: Industrially Pure Titanium Grades GR1, GR2, and GR3
Industrially pure titanium is categorized chiefly as GR1, GR2, and GR3. The grades differ by interstitial impurity contents (O, N, H):
As impurity content increases from GR1 → GR2 → GR3:
Strength (yield and tensile) increases.
Plasticity (ductility) decreases.
At room temperature, commercially pure titanium shows relatively low yield strength and ultimate tensile strength compared to many steels, but it possesses:
Excellent ductility and toughness.
Outstanding corrosion resistance in many oxidizing and chloride-bearing media.
Good weldability.
Low coefficients of thermal expansion and thermal conductivity, which influence welding heat flow and distortion behavior.
3. Welding Metallurgy of Titanium: Heat Input and Cooling Rate Effects
Research and shop practice indicate:
Titanium’s high melting point, low thermal conductivity, and low specific heat lead to steep thermal gradients and sensitive heat-affected zones (HAZ).
With increasing welding line energy (heat input), the HAZ overheated region experiences longer high-temperature residence and slower cooling, promoting coarse grain growth and a reduction in local plasticity.
Conversely, excessively rapid cooling favors the formation of finer, supersaturated solid solutions that can slightly diminish weld metal plasticity and toughness.
Both overly slow and overly fast cooling can result in suboptimal ductility at the joint.
A practical cooling rate window of approximately 10–200 °C/s is suitable. For a given wall thickness, cooling rate is largely governed by welding line energy and shielding effectiveness.
4. Standards and Requirements for Titanium Tube Welding
4.1 Pre weld Preparation
Power source: DC GTAW/TIG machine equipped with:
High-frequency start to avoid tungsten inclusion.
Current downslope to fill the crater.
Post flow gas timer to protect hot metal from atmospheric contamination.
Water-cooled leads/torch due to high current demand when welding titanium.
Filler and shielding:
Filler wire: ER TA1.
Shielding gas: Argon, 99.99% purity.
Tungsten electrode: Suitable thoriated/lanthanated/ceriated tungsten as specified by procedure.
Joint design: Single-V groove (machined).
Positioning: Use rolling support platforms to ensure ergonomic, stable manipulation and consistent torch angle.
Procedure qualification: Perform welding trials and qualify WPS/PQR before production.
Table 1
| Main parameters of welded titanium tube | |||
| Pipe wall (mm) | ≤2 | 3-4 | |
| Bevel angle | form | 1 | 1 or 60°V type |
| Pure edge(mm) | 1-1.5 | ||
| Gap (mm) | 0~1 | 0~1 | |
| welding wire | Brand | ERTA2 | ERTA2 |
| Diameter (mm) | φ2 | φ2 | |
| Tungsten wire diameter(mm) | φ1.6 | φ2 | |
| Nozzle aperture(mm) | φ12-16 | φ16-20 | |
| Welding layer | 1 | 2 | |
| Interlayer temperature ℃ | ≤200 | ≤200 | |
| Welding current A | 40-70 | 80-110 | |
| Welding voltage V | 10-12 | 12-14 | |
| Welding speed(cm/mm) | 7.5-10 | 10-15 | |
| Krypton gas flow//min | welding torch | 8-12 | 12-15 |
| inside the tube | 8-10 | 10-15 | |
4.2 Welding Environment and Technique
Environment: Clean, enclosed room with ambient airflow below approximately 2 m/s. Segregate titanium welding from ferrous work; cover floors with rubber to prevent iron contamination; prohibit welding in air containing iron dust.
Segmental, intermittent GTAW without trailing shield cup:
Each segment: 10–15 mm length; 5 s from arc initiation to extinguish.
Post flow argon: 20–25 s after arc extinction to protect the hot puddle and HAZ until below about 250 °C.
Resume welding only after the previous segment cools below about 500 °C, repeating until the seam is complete
Pool control: Keep a small, well-controlled molten pool; ensure sound tie-ins between segments to avoid lack of fusion or arc strikes.
Internal purge: Back purge the tube fully with argon to prevent internal oxidation (discoloration/gray oxides) of the root.
Cleaning: Degrease filler wire with acetone; clean groove faces and 25 mm on each side with acetone immediately prior to welding; wear powder free gloves.
Post weld cleaning: Pickle the weld and HAZ; then rinse thoroughly with clean water to remove residual acid and prevent corrosion initiation.
Maintain low oxygen, nitrogen, and hydrogen exposure at all times. Titanium at temperatures above 400–450 °C is highly reactive; adequate primary, trailing, and backside shielding is essential if continuous welding is used.
Optimize heat input to stay within the cooling rate window (10–200 °C/s), balancing grain size control with avoidance of brittle supersaturated phases.
For tube sizes 18–133 mm and up to 3 mm wall, GTAW parameters typically fall in low to medium current ranges with tight arc length, modest travel speed, and controlled interpass temperatures.
5. Post-Weld Quality Inspection and Qualification
5.1 Using the process parameters above, titanium tube welds were evaluated by:
Macroscopic cross section examination and low magnification metallography: No internal porosity, lack of fusion, or hot cracks detected; fusion and penetration profiles were sound; no intergranular or transgranular cracking observed.
Pressure testing: Hydrostatic test at 0.5 MPa across all titanium tube circuits showed no leakage.
Visual and color inspection: Weld surfaces displayed acceptable straw to silver coloration, indicating adequate shielding; absence of blue/gray suggests minimal oxidation.
Recommended additional NDE (as applicable to code/spec):
Dye penetrant testing (PT) for surface defects.
Radiography or phased array UT for volumetric inspection on critical joints.
Hardness surveys to confirm no excessive embrittlement.
Oxygen/nitrogen pickup checks when specialized instrumentation is available.
5.2 Performance Outcomes in Chemical Service
· Corrosion resistance: GR2 titanium tube provided robust resistance in chlorate production media, enabling reduced corrosion allowance and longer run lengths.
· Mechanical reliability: Controlled heat input and cooling delivered balanced HAZ plasticity and weld toughness, minimizing risk of brittle failures.
· Maintainability: Clean weld roots from proper back purging facilitated low-fouling interiors and stable hydraulic performance.
· Lifecycle economics: Despite higher initial material cost, the titanium tube solution decreased downtime and extended overhaul intervals, improving total lifecycle value.
5.3Best Practices Summary for Titanium Tube Welding in Chemical Plants
Select GR2 titanium tube where a superior corrosion-strength balance is required; consider GR1 for maximum ductility and GR3 where higher strength is essential and ductility trade offs are acceptable.
Enforce stringent cleanliness, gas purity, and shielding protocols; avoid any ferrous contamination.
Use qualified GTAW procedures with controlled segment lengths, post-flow, internal purge, and verified interpass temperatures.
Target cooling rates between 10–200 °C/s by managing line energy and heat sinking; avoid extremes of quenching or excessive heat soak.
Conduct thorough post-weld cleaning and comprehensive inspection (visual, PT, macro/micro, pressure test), and apply NDE per criticality.
Summary of Strong Oxidant Production Equipment
For corrosive chemical processes such as KClO3 production, GR2 pure titanium tube stands out for its weldability, corrosion resistance, and dependable mechanical performance. By rigorously controlling welding parameters—particularly shielding, line energy, and cooling rate—and by applying robust post weld quality inspection, operators can realize the full benefits of titanium tube systems: higher reliability, longer service life, and reduced total cost in demanding chemical environments.
