How to Weld HK-40 Cracking Furnace Tubes with E310-16 Electrode
HK-40 and HP-Nb are the classic 25Cr-20Ni cast heat-resistant tubes used in ethylene cracking furnaces and hydrogen reformers, where service temperatures reach 1000–1100 °C. AWS A5.4 E310-16 is the go-to SMAW filler for site butt welds and radiant-tube repairs. Here is a field-workshop procedure.
Confirm the base-metal grade first
HK-40 (0.35 – 0.45 % C) → for full-strength matching welds use the high-carbon variant E310H-16 / A432; use E310-16 only for repair build-up where a slight strength deficit is acceptable.
HP-Nb or standard 310/310S/310H → E310-16 is the correct filler.
Bevel Preparation and Preheating
Prepare a U-shaped bevel (60° included angle, 2 mm root face) using machining or grinding. Remove oxide scale from the areas extending 25 mm on either side of the bevel until a metallic luster is exposed. Preheat to 100–150°C to remove moisture, as HK-40 castings absorb moisture during service; the preheating step may be omitted only for new pipes.
Current, polarity and welding pass sequence
| Diameter | DCEP amperage (5G / 6G pipe positions) |
|---|---|
| Ø 2.5 mm | 60 – 90 A |
| Ø 3.2 mm | 75 – 110 A |
| Ø 4.0 mm | 95 – 150 A |
- Redry electrodes 250 – 350 °C × 1 h; keep in 80–150 °C quiver.
- DCEP preferred; short arc, stringer beads only (weaving < 2 × electrode diameter).
- Interpass temperature ≤ 150 °C - E310-16 weld metal is fully austenitic (FN ≈ 0) and hot-crack sensitive if the pool is kept large.
Post-weld inspection
100% PT (dye penetrant testing) is performed on the weld cap and root, and RT (radiographic testing) is conducted on highly critical joints. Post-weld heat treatment (PWHT) is not performed; E310-16 filler metal is used in the as-welded condition, as PWHT could induce sigma-phase embrittlement.
FAQ
Q: Can I use E309-16 instead?
A: No. E309-16 (23Cr-13Ni, oxidation limit ~ 1000 °C) will scale rapidly at HK-40 service temperature. Always match with 25Cr-20Ni family.
Q: When must I use E310H-16 instead of E310-16?
A: When the tube is HK-40 (high C) and the joint must carry full creep-rupture strength at 1000+ °C - the H grade has C ≤ 0.45 % matching the base cast.
Q: Does E310-16 need preheat?
A: Only 100 – 150 °C to remove moisture; no metallurgical preheat is required.
