What ASTM B862 Grade 4 Welded Pipe Covers
ASTM B862 is the specification for welded titanium and titanium alloy pipe produced with or without filler metal, and Grade 4, UNS R50700, is the highest strength of the four commercially pure grades listed in it. Compared with Grades 1 to 3, Grade 4 carries a higher permitted oxygen content, which raises tensile and yield strength while the material stays single phase alpha and therefore fully weldable. Pipe is supplied as-welded, annealed, or annealed and pickled, and the longitudinal seam is examined by radiographic or ultrasonic testing as agreed when the order is placed.
Chemistry and Mechanical Property Limits
The Grade 4 analysis in ASTM B862 is controlled to a maximum of 0.40% oxygen, 0.05% nitrogen, 0.08% carbon, 0.0125% hydrogen and 0.50% iron, with titanium as the balance. Specified room temperature minima are 550 MPa (80 ksi) tensile strength, 483 MPa (70 ksi) 0.2% offset yield strength and 15% elongation in a 50 mm gauge length. Nominal density is 4.51 g/cm3 and the alloy melts at approximately 1668 C, so it tolerates moderate elevated temperature service provided oxygen and iron are held inside the limits during welding and heat treatment.
| Property | ASTM B862 Grade 4 Requirement |
|---|---|
| Oxygen, max | 0.40% |
| Nitrogen, max | 0.05% |
| Hydrogen, max | 0.0125% |
| Iron, max | 0.50% |
| Tensile strength, min | 550 MPa (80 ksi) |
| Yield strength, 0.2% offset, min | 483 MPa (70 ksi) |
| Elongation in 50 mm, min | 15% |
Service Environments and Typical Applications
Grade 4 is selected when the additional yield strength over Grade 2 allows a thinner wall, a lighter assembly or a higher pressure rating within the same envelope. It retains the passive oxide film that makes unalloyed titanium resistant to chlorides, hypochlorite, nitric acid and mildly reducing media, so it performs well where stainless steel would pit or stress corrosion crack.
Hydraulic, instrumentation and impulse tubing for process plants.
Heat exchanger and condenser shells, water boxes and connecting piping.
Chemical process equipment such as pickling baskets, reaction vessel internals and transfer lines.
Cryogenic vessels and airframe support hardware.
Desalination trains and offshore seawater circuits.
Welding, Finishing and Testing of B862 Pipe
Seam quality decides the value of the pipe. Heat input is kept low, interpass temperature is controlled, and the molten pool plus the hot root are shielded until the metal falls below roughly 400 C, because titanium absorbs oxygen, nitrogen and hydrogen above that temperature. Shielding argon is specified at 99.99% purity or better, the internal purge is checked for dew point, and hoses are non-permeable rather than rubber. A bright silvery weld is acceptable; straw, blue or grey colour indicates contamination and calls for cut-back and rewelding. Pressure service fabrication follows the procedure qualification and cleanliness rules of ASME Boiler and Pressure Vessel Code Section IX. Standard mill tests include spectrographic chemical analysis, tensile testing, flattening, hydrostatic or eddy current examination and radiography of the weld seam. Each lot ships with an EN 10204 3.1 mill test certificate and third party inspection can be arranged.
Ordering Points That Prevent Rework
State outside diameter, wall thickness, length, weld type, heat treatment condition, end finish and the level of seam examination required. Quoting the UNS number and the edition of ASTM B862 on the purchase order removes any ambiguity about chemistry and property limits. For thin wall pipe below about 3 mm, flattening and reverse flattening become demanding tests, so agree on test frequency before rolling starts. Instrumentation lines are usually ordered bright annealed, while larger process pipe is normally pickled to give a clean oxide free surface for welding in the field.
Frequently Asked Questions
Q: Is Grade 4 stronger than Grade 2 titanium pipe?
A: Yes. ASTM B862 sets Grade 4 at 550 MPa minimum tensile and 483 MPa minimum yield, against 345 MPa and 275 MPa for Grade 2, so Grade 4 offers roughly 75 percent more yield strength.
Q: Can Grade 4 be welded the same way as Grade 2?
A: The welding procedures are essentially the same. Both are alpha titanium that must be shielded from air until the weld cools below about 400 C, and both require 99.99% argon and a monitored purge.
Q: What is the maximum service temperature for R50700 pipe?
A: Continuous service is normally limited to about 315 C because strength falls and oxidation accelerates above that level. Higher temperatures require alloyed grades rather than commercially pure titanium.
Q: Which delivery condition is best for pressure lines?
A: Annealed pipe is standard for pressure service because it removes residual stress from forming and welding. Bright annealed or pickled surfaces are chosen according to whether the pipe will be welded on site or used for instrumentation.
Q: What documents accompany a shipment?
A: An EN 10204 3.1 mill test certificate covering chemistry, tensile properties and any non-destructive tests, plus dimensional records. Certified third party inspection is available on request.
