Most tubing orders boil down to one question: what does this line carry, and where does it run? Answer that and the alloy choice usually narrows to one of three: 304, 316, or 316L. Every other decision — seamless vs welded, hardness, finish, certification — flows from those two answers.

304 is the default for most general-service work: instrument air, lube oil, fuel oil, cooling water, dry process gas. 316 adds molybdenum for better resistance to chlorides and many process chemicals. 316L drops the carbon further to prevent welding and high-temperature degradation. The cost step from 304 to 316L runs roughly 30-50% but the lifetime cost favors 316L on any chemical or marine service.

• 304 stainless: 18% chromium, 8% nickel, 0.08% maximum carbon. General-service workhorse. Handles freshwater, instrument air, fuel oil, lube oil, and most non-chloride chemistry.
• 316 stainless: 16% chromium, 10% nickel, 2% molybdenum. The molybdenum step gives much better pitting resistance against chlorides, seawater, and many process chemicals.
• 316L stainless: Same chemistry as 316 with carbon capped at 0.03% (vs 0.08% on standard 316). The lower carbon prevents chromium-carbide precipitation during welding and at sustained temperatures above 800°F.

1. Any tubing that will be welded — including orbital welding for UHP service.
2. Sustained service temperatures above 800°F.
3. Sour service (NACE-certified L grade specifically).
4. Cryogenic service — impact-tested 316L holds toughness to -325°F.
5. Any service where the lifetime cost of a corrosion failure exceeds the alloy upgrade cost.

• Seamless tubing is drawn from a solid billet. No weld seam. Higher cost. Higher pressure rating. Required for the highest-integrity service.
• Welded tubing is rolled from flat strip and seam-welded longitudinally. Lower cost. Lower pressure rating at the seam. Adequate for most general-service work.
• Welded and drawn (WD) tubing is welded then drawn through a die to homogenize the wall. Better than welded, less expensive than seamless. Common compromise for medium-pressure service.

• Mill finish (10-20 Ra): Standard general-service tubing. Adequate for most non-critical work.
• Mechanically polished (5-10 Ra): Improved corrosion resistance, suitable for chemical service.
• Electropolished (3-5 Ra): Required for UHP semiconductor and pharmaceutical service.
• Pickled and passivated: Removes scale and surface contamination. Standard for new installations on chemical service.

Compression fittings require the tube to be softer than the ferrule. The standard requirement: tube hardness below Rockwell B 90 (or equivalent HV 200). Annealed tubing meets this comfortably. Cold-drawn hardened tubing does not — the ferrule cannot bite, the seal does not develop, and the fitting leaks under pressure.

Always specify “fully annealed” on the purchase order. Verify the hardness on the mill certification. For high-pressure or critical service, request a hardness test on each lot.

• Mill test report (MTR): Chemical composition, mechanical properties, heat number, mill identification. Standard on all stainless tubing orders.
• NACE MR0175: Required for sour service. Verifies hardness within NACE limits.
• ASTM A269/A312/A213: Standard tubing specifications. A269 for instrumentation, A312 for pipe, A213 for boiler/heat-exchanger.
• 3.1 certification: European EN 10204 standard, equivalent to MTR with stricter traceability.
• Pressure test: Confirms the tube held the specified test pressure. Standard on welded and high-pressure tubing.

• Oil and gas: 316L for instrumentation, sour-service certified. Inconel 625 for high-H₂S and offshore.
• Chemical processing: 316L for general process. Hastelloy or Inconel for aggressive chemistry.
• Power generation: 304 for cold service, 316L for mid-temperature, Inconel 600/625 for hot.
• Pharmaceutical: 316L electropolished, with documented surface finish and cleanliness.
• Semiconductor: 316L low-sulfur electropolished, cleanroom packaged.
• Food and beverage: 316L sanitary, mirror finish, 3-A certified.
• Aerospace: 304 and 316L with specific aerospace certifications (AMS).

• Ordering 304 for chloride service. The chloride attacks the alloy. Pitting follows in months.
• Ordering 316 instead of 316L for welded service. Welding standard 316 precipitates chromium carbides at the heat-affected zone, opening the door to intergranular corrosion.
• Skipping the hardness check. Cold-drawn tube too hard for the ferrule causes leak failures on first pressure test.
• Mixing wall thicknesses in one run. Different wall thicknesses change the OD precision and may cause ferrule-set mismatch.
• Not specifying annealed condition. The mill defaults to cold-drawn unless told otherwise.

Standard imperial sizes (1/8″ through 1″ OD) in 304, 316, and 316L. Seamless and welded options. Standard 0.020″ through 0.083″ wall thicknesses. Custom cut to length on request. Same-day shipping on in-stock items.

For specialty alloys (Inconel, Monel, Hastelloy, Duplex 2205), depot stock ships within 2-5 days. Mill orders for non-standard combinations run 4-12 weeks.

Need stainless tubing today? Call Collins-Oliver or browse our tubing inventory. 304, 316, 316L in seamless and welded — same-day pickup, no minimum order.