904L Stainless Steel Lined Clad Pipe | UNS N08904 / 1.4539 High Alloy Cladding for Sulfuric & Phosphoric Acid Service – Womic Steel

Q1: When should I choose 904L over 316L for clad pipe?
A: Choose 904L when the service involves sulfuric acid, phosphoric acid, formic/acetic acid, or when 316L shows pitting or general corrosion in your environment. 904L is also better for warm seawater (higher chlorides). If the fluid is only slightly acidic with no chlorides, 316L may suffice.

Q2: What is the maximum temperature for 904L?
A: In corrosive service, 904L is typically limited to 350-400°C. Above that, the material may sensitize or lose corrosion resistance. For high temperature acid service (>400°C), consider Alloy 825 or 625.

Q3: Can 904L be used for sour gas (H₂S) service?
A: NACE MR0175 / ISO 15156 permits 904L for sour service only in very mild conditions: low H₂S partial pressure, low chlorides, pH >3.5, temperature <60°C. For typical sour wet gas, Incoloy 825 is preferred.

Q4: What filler metal should be used for welding 904L clad pipe?
A: For the inner pass (904L to 904L), use Alloy 625 (ERNiCrMo-3) or 904L filler (ER385). Alloy 625 is more common and provides higher safety. Do not use 316L filler.

Q5: Is 904L clad pipe available in small diameters (e.g., 2″) for instrumentation?
A: Yes, through our seamless extrusion process. Minimum OD is approximately 25 mm (1″). Cladding thickness 2.02.5 mm.

Q6: How does 904L compare to Alloy 28 (UNS N08028)?
A: Both are high alloy austenitics with similar PREN (34 vs 38). Alloy 28 has higher Cr and Ni, and better resistance to high chloride + high temperature pitting. For sulfuric acid, both are excellent. Alloy 28 is slightly more expensive. 904L is more common in North American acid plants; Alloy 28 in European specifications.

Q7: Can you supply 904L clad pipe with A333 Gr.6 backing for low temperature service?
A: Yes. 904L remains ductile at low temperature; the A333 Gr.6 backing is impact tested at -45°C. The combination is suitable for arctic acid pipelines (rare but possible).

Q8: Do you provide assurance that the cladding is free from dilution by carbon steel?
A: Yes. The vacuum hot roll bonding process prevents oxidation and minimizes diffusion. We perform PMI on the cladding surface to verify composition. The dilution zone is typically only a few microns thick and is not exposed to the fluid.

Q9: What is the typical yield strength of 904L cladding?
A: 904L has a yield strength of approximately 220 MPa (32 ksi) in the annealed condition. This is lower than carbon steel backing but the cladding thickness is small; the carbon steel core carries the hoop stress. For pressure design, we use the backing steel wall thickness only; the cladding is considered a corrosion allowance.

Q10: Do you offer beveled ends with 904L buttering?
A: Yes. We can prepare bevels (30-35°, 1.6 mm land) and apply a weld overlay (buttering) of Alloy 625 or 904L filler on the bevel face. This prevents dilution of the 904L cladding during field girth welding.

Q11: Can you supply 904L clad heat exchanger U-bend tubes?
A: Yes, for seamless clad pipe (OD ≤168 mm). We cold bend, stress relieve, and 100% NDT (PT or ET) the bend area. U-bends for acid services are common in chemical plants.

Q12: How do I order a small trial quantity?
A: Provide OD, core WT, cladding thickness, length (m), and backing steel grade. We will quote a trial batch (e.g., 50100 meters). Expect a price premium for small quantities.