Types of Metal Tubing: Round, Square, Rectangular and Mechanical is the kind of question that becomes expensive when it is answered with a rule of thumb instead of a complete material specification.
Pipe and tube can look similar while being dimensioned for different purposes. Nominal pipe size, outside diameter, schedule, wall thickness, tube dimensions, seam type and material grade need to be stated explicitly before quoting or fabrication begins.
Type names are a useful first filter, but they are not a substitute for dimensions, material grade, finish and the project design. Selection should move from function to specification.
Key takeaways
- Know whether the callout is pipe or tube.
- For pipe: NPS + schedule/wall + grade.
- For tube: actual dimensions + wall + grade.
- Include end condition, cuts and fittings.
- Check coating and certification requirements.
Know how the product is dimensioned
Nominal pipe size is not a direct measurement of outside diameter for most common pipe sizes. Schedule changes wall thickness while OD stays tied to NPS. Mechanical/structural tubing is commonly ordered by actual OD or outside dimensions plus wall.
DOM is a manufacturing/process description used for close-tolerance mechanical tubing; ERW describes electric-resistance-welded production. End use and specification control which is appropriate.
Use “type” as the first decision, not the last
Type narrows the field by function or manufacturing form. The second step is to define size, grade, finish and performance requirements within that type. For systems with hardware or accessories, compatibility should be verified as part of the same takeoff. This prevents an order that contains individually correct parts that do not work together.
What to put on the RFQ
For pipe, provide nominal size, schedule/wall, grade/specification, length, end condition and quantity. For tubing, give actual outside dimensions and wall thickness. Add fittings, flanges, valves, bevels, cuts and certification requirements to the same takeoff so the package is compatible.
Tampa Bay jobsite considerations
Exterior piping and fabricated tube assemblies in Florida should consider coatings and trapped-water details. Galvanizing or alternate alloys can be appropriate, but the service fluid, pressure and governing piping specification control industrial systems.
Common mistakes to avoid
- Confusing nominal pipe size with measured outside diameter.
- Using schedule language for tubing without confirming actual wall.
- Leaving seam/manufacturing specification undefined for mechanical applications.
- Ordering fittings/flanges separately without checking pressure class and compatibility.
- Forgetting bevels, end prep, cuts or coating requirements.
Why this choice affects the rest of the job
Pipe/tube dimensions control fittings, clamps, machined parts and weld joints. Verify the actual dimensional convention before any mating component is fabricated.
When the supplier should not make the engineering decision
Material suppliers can clarify product dimensions, availability, processing and logistics. They should not silently redesign structural, hydraulic, pressure, fire/life-safety or tested-impact requirements. When a proposed alternate changes a design property or an approved system, route it through the engineer, specifier or authority that owns that requirement before release.
From takeoff to delivery
- Define: confirm the drawing/specification and quantities.
- Quote: include processing, finish, certifications and permitted alternates.
- Review: compare proposals on equivalent scope—not just unit price.
- Coordinate: confirm required date, truck access, unloading and site contact before dispatch.
Frequently asked questions
What information should I include in the RFQ?
For pipe, provide nominal size, schedule/wall, grade/specification, length, end condition and quantity. For tubing, give actual outside dimensions and wall thickness. Add fittings, flanges, valves, bevels, cuts and certification requirements to the same takeoff so the package is compatible.
Can Steel & Pipe Supply help source material that is not shown online?
Online listings are not a complete picture of every size or sourcing option. Send the specification, quantity and required date so the sales team can check local inventory and broader warehouse/supplier availability.
Can material be cut or processed before delivery?
Processing depends on material, size, quantity, tolerance and the requested operation. Include cuts, holes, bends or other processing on the RFQ so capability and lead time can be confirmed before the order is placed.
Request a material quote
Steel & Pipe Supply works with contractors, fabricators, industrial buyers and the general public. Send the material list, drawing or specification and the team can review sourcing, processing and delivery options for Tampa Bay projects or nationwide shipment.