Stainless Steel Specialists
Seamless & Welded Pipe
Stainless steel and corrosion-resistant alloys. NPS 1/4" through 36", schedules 10S through XXH, in seamless and welded form.
Standard: ASTM A312 · ASME SA312
Sizes: 1/4" – 36" NPS
Schedules: 10S · 40S · 80S · 160 · XXH
Overview
What We Stock
Pipe is the workhorse of any pressure-containing piping system, and the conversation always starts with three variables: size, schedule, and material. Unified Alloys stocks austenitic stainless steel pipe to ASTM A312 / ASME SA312 in nominal pipe sizes from 1/4″ through 36″, across the schedule range from 10S through 160 and XXH. Common grades — 304, 304L, 316, 316L — are deep stock. Higher-alloy and chrome moly grades are project-order or partial stock; lead times vary.
Pipe ships in 20′ lengths as standard. Double random lengths (~40′) are available on certain sizes to suit project requirements. Plain end (PE) is the default supply form; bevelled end (BE) and threaded end (TE) preparations can be supplied on request, machined in-house at any of our five Canadian branches.
The seamless-versus-welded decision sits with your piping engineer and depends on service conditions, code requirements, and cost tolerance. We stock both forms across the common size range and discuss the trade-offs in detail further down this page.
Sizes above 36" NPS, non-standard wall thicknesses, and project-grade chrome moly orders are quoted on request. Lead times depend on mill availability and material specification.
Key Applications
- Process piping in oil and gas, refining, and petrochemical service
- Steam, water, and instrument lines in power generation and pulp mills
- Corrosion-resistant lines in chemical and food processing
- Mining slurry, tailings, and process water systems
- Marine and offshore pressure piping
Materials & Grades
Available Materials
Pipe is stocked across austenitic stainless and supplied on request in higher-alloy and chrome moly grades. All material conforms to ASTM / ASME specifications and can be supplied with MTRs traceable to the heat number.
The core stocking range. Standard choice for corrosion resistance in chemical processing, refining, food-grade, and general industrial pressure service.
304 · 304L · 316 · 316L · 317L · 321 · 347
For chloride-rich service, seawater, and high-strength applications where standard austenitics fall short. Available on request.
2205 · 254SMo
For severe corrosion environments, high temperatures, and aggressive chemical service. Project-order in most sizes.
Monel · Inconel
For high-temperature power and process service, particularly steam and refinery heater lines governed by ASME B31.1 and B31.3 code. Project-order.
P5 · P9 · P11 · P22 · P91
Form & Production Method
Seamless vs Welded
Welded pipe is formed by rolling a flat plate (skelp) into a tube and welding the longitudinal seam. Seamless pipe is produced by piercing a solid billet and drawing it through dies to final dimension. Both forms are supplied to the same ASTM A312 / ASME SA312 standard and meet the same chemical, mechanical, and dimensional requirements. The decision between them is driven by service conditions, code, lead time, and cost.
Advantages of Welded
Welded pipe is typically more cost-effective and more readily available than seamless. Mill lead times are shorter, which protects schedule and limits exposure to commodity price movement on long-lead orders. Wall thickness tends to be more consistent than seamless, and the internal surface of the skelp can be inspected before forming, which is not possible with a pierced billet.
Advantages of Seamless
Seamless pipe has no longitudinal weld, which removes the seam as a potential failure point and is often specified for high-pressure, high-temperature, or critical-service applications where code or owner preference dictates. Roundness and ovality are typically better than welded. For procurement teams, the seamless preference is often a peace-of-mind specification rather than a strict code requirement — worth confirming with engineering before defaulting to seamless on cost.
Selection of pipe production method should be made through consultation with your piping engineer, taking into account service conditions, code requirements, and project economics.
Technical Data
Dimensional Data
For complete dimensional data including wall thickness, weight per foot, inside diameter, and theoretical burst pressure across all schedules, see our full ASTM A312 reference chart.
Stainless Steel Pipe Chart
Full dimensional data by pressure class
Regulatory & Traceability
Material Traceability & CRN
Pipe used in CRN-registered pressure systems in Alberta, British Columbia, Saskatchewan, Ontario, and other provinces must conform to the material specification listed on the registration. Pipe itself is not separately registered — the system carries the CRN — but the material supplied must match the registered grade and standard, and traceability documentation must support that match.
Mill Test Reports (MTRs) traceable to the heat number can be supplied with orders, confirming chemical composition, mechanical properties, and conformance to ASTM A312 / ASME SA312. For Alberta projects in particular, where ABSA documentation requirements are well established, traceability is treated as a routine part of supply rather than an exception.
If your project requires specific NACE conformance (MR0175 / MR0103 for sour service), positive material identification (PMI), or third-party material verification, our technical sales team can confirm availability and quote accordingly.
FAQ
Frequently Asked Questions
Should I spec seamless or welded?
The honest answer is that your piping engineer makes this call, not procurement. Both forms meet the same ASTM A312 specification and the same dimensional and mechanical requirements. Welded is usually faster and less expensive. Seamless is often specified for high-pressure, high-temperature, or critical service where the absence of a longitudinal weld matters. In a lot of cases, seamless gets specified out of preference rather than code requirement — worth a five-minute conversation with engineering before defaulting to seamless on a large bill of materials.
What's the difference between pipe and tube?
Pipe is specified by Nominal Pipe Size (NPS), which is the inside diameter for small sizes and a nominal reference for sizes above 12″. For sizes 12″ and below, the outside diameter is fixed and the inside diameter changes with wall thickness (schedule). Tube is specified by actual outside diameter and wall thickness, with the inside diameter calculated from there. Pipe is the standard for pressure-containing piping systems governed by ASME B31 codes. Tube is used for instrumentation, heat exchangers, structural applications, and other contexts where the OD is the dimensional reference. They are not interchangeable.
Can MTRs be supplied with our order?
Yes. Mill Test Reports traceable to the heat number are available on request and routinely supplied for pressure-system and CRN-registered applications. MTRs confirm chemical composition, mechanical properties, and conformance to ASTM A312 / ASME SA312. NACE MR0175 / MR0103 conformance for sour service and Positive Material Identification (PMI) verification are also available — confirm requirements at the time of quote.
Do you stock chrome moly pipe and non-standard wall thicknesses?
Chrome moly grades (P5, P9, P11, P22, P91) are project-order rather than stocked, with lead times depending on the grade, size, and mill availability. Non-standard wall thicknesses and sizes above 36″ NPS are also quoted on request. For project planning, send us your bill of materials early — chrome moly P91 in particular can carry significant lead time, and locking in mill space early protects schedule.
Ready to Order or Need Help Sizing?
Our technical sales team can help you select the right size, material, and configuration for your application.