Stainless fittings are the backbone of food and beverage, marine, chemical and water-treatment piping. US online and wholesale catalogues list 304 and 316 in three main formats: cast Class 150 threaded fittings, forged 3000# threaded and socket-weld fittings, and butt-weld fittings in schedules 10S to 80S. Each format comes from a different production route — and a different risk profile.
304 or 316, L or not?
- 316/316L contains molybdenum for better chloride resistance. It is the default for marine, coastal and chemical use.
- L grades (low carbon) reduce sensitisation after welding. They are expected for socket-weld and butt-weld fittings.
- Duplex (2205, 2507) and higher alloys are niche, high-value items. They are often air-freighted in small lots.
Three formats, three production routes
| Format | Made by | Key checks |
|---|---|---|
| Class 150 threaded / socket-weld (MSS SP-114) | Investment casting, CF8/CF8M | Porosity, thread gauging, pressure test |
| 3000# forged (ASME B16.11) | Forging bar, A182 F304L/F316L | Wall thickness, heat-code marking, MTR |
| Butt-weld (ASME B16.9, A403) | Formed from pipe or plate, WP-S / WP-W / WP-WX | Bevel ends, wall thickness, weld radiography (WX) |
Surface and corrosion details buyers notice
- Pickling and passivation after welding or machining. Free iron contamination shows up as rust spots after the ocean voyage.
- Do not pack stainless with carbon-steel tools or strapping. Contact contamination causes staining.
- Thread and bevel protectors, so fittings arrive ready to install.
Duty picture for stainless fittings
- HTS 7307.21–7307.29 — see HTS and tariffs.
- Section 232 steel derivative duty on full value, where the line is listed.
- AD orders on stainless butt-weld fittings from Malaysia, the Philippines and Italy. Check carefully when sourcing butt-weld fittings from these countries or from plants that use their inputs — see AD on fittings.
DDP to the distributor
Stainless distributors hold many small SKUs. A DDP programme with mixed-SKU pallets, carton labels by part number and an MTR pack per shipment lets them restock without dealing with customs. Consolidating from several workshops in Vietnam into one container keeps freight per piece low. Each supplier's origin must still be recorded line by line.
Related: ASME and ASTM standards · packing fittings.