What Is Mechanical Tubing?
Mechanical tubing is tube manufactured to meet specific end-use requirements rather than pressure ratings. It is produced to controlled dimensions, tolerances and chemical compositions, which results in more consistent performance across the entire tube compared with standard pipe. Mechanical tube can be supplied to standard specifications on request, but it is usually produced to typical properties focused on yield strength, machinability and surface finish for the intended application.
Types and Governing Standards
| Type | Representative Standard |
|---|---|
| Seamless mechanical tubing | ASTM A519 |
| DOM (drawn over mandrel) tubing | ASTM A513 T5 |
| ERW mechanical tubing | ASTM A513 T1 / T2 |
| Structural tubing / HSS | ASTM A500 |
| Precision steel tubes | EN 10305, DIN 2391, GB/T 3639 |
| Carbon steel tubes for machinery | JIS G3445 |
Common size ranges for mechanical tube are outside diameters from 10.3 mm to 762 mm, wall thicknesses from 6 mm to 35 mm, and delivery lengths of 5.8 m, 6 m, 11.8 m or 12 m. Standard and grade selection depends on the application: general structure and mechanism, construction, machinery, transportation, aviation and petroleum equipment.
Chemical Composition and Mechanical Properties
The table below shows typical values for common carbon steel mechanical tube grades.
| Standard | Grade | C (%) | Si (%) | Mn (%) | P (%) | S (%) | Tensile (MPa) | Yield (MPa) | Elongation (%) |
|---|---|---|---|---|---|---|---|---|---|
| DIN 1629 | St37 | 0.17 max | - | - | 0.040 max | 0.040 max | 350 - 480 | 235 min | 25 min |
| DIN 1629 | St44 | 0.21 max | - | - | 0.040 max | 0.040 max | 420 - 550 | 275 min | 21 min |
| DIN 1629 | St52 | 0.22 max | 0.55 max | 1.60 max | 0.040 max | 0.035 max | 500 - 650 | 355 min | 21 min |
For European structural and mechanical applications, DIN 1629 grades are now commonly specified under EN 10210 or EN 10297, where St37, St44 and St52 correspond broadly to S235, S275 and S355 designations.
Dimensional Tolerances
Mechanical tube tolerances are defined for both cold-drawn and hot-finished product. Cold-drawn seamless tube offers tighter outside diameter and wall thickness control:
| Condition | OD Tolerance | Wall Thickness Tolerance |
|---|---|---|
| Cold-drawn, OD up to 1.699 in. | +/- 0.005 in. | +/- 10% (ID under 1.5 in.) |
| Cold-drawn, OD 1.700 - 2.099 in. | +/- 0.006 in. | +/- 10% (ID under 1.5 in.) |
| Cold-drawn, OD 2.100 - 2.499 in. | +/- 0.007 in. | +/- 10% (ID 1.5 in. and over) |
| Hot-finished, OD 2.000 - 2.499 in. | +/- 0.017 in. | +/- 10% to 12.5% depending on OD |
Wall thickness tolerance for mechanical tube is typically expressed as a percentage of the nominal wall, with tighter values for thin-wall product and looser values above 25% of the outside diameter. Quenched and tempered product carries combined OD and ID tolerances to reflect distortion from heat treatment. When a project needs very tight tolerances, DOM (drawn over mandrel) tube is the usual choice because it controls both inside and outside surfaces.
Applications of Mechanical Tubing
Mechanical and equipment uses
Solar racking and mounting systems.
Agricultural and dairy equipment.
Greenhouse structures and equipment.
Conveyor rollers, trailers and carports.
Appliances, canopies and shade structures.
Satellite dish supports and vinyl stiffening tubes.
Structural uses
Structural tubing, often called hollow structural sections (HSS), is used where standard strength requirements of the tube dictate the application. HSS is available in round, square and rectangular shapes and is used in buildings, bridges, towers, cranes, sign supports and poles, offshore production and drilling platforms, and roll-over protective structures (ROPS).
In tall buildings, the tube system is a structural concept in which the building resists lateral loads such as wind and seismic forces by acting as a hollow cylinder cantilevered from the ground. The system can be built in steel, concrete or composite construction, and most buildings above 40 stories built since the 1960s use this structural type.
FAQ
Q1. What is the difference between mechanical tubing and pipe?
Mechanical tubing is produced to meet specific end-use requirements such as yield strength, machinability, surface finish and tight tolerances, while pipe is normally produced to pressure and dimensional standards for fluid conveyance.
Q2. What is DOM tubing?
DOM (drawn over mandrel) tubing is cold-drawn ERW tubing to ASTM A513 T5. Drawing over a mandrel controls both the inside and outside diameter, giving very tight tolerances and a smooth bore.
Q3. What standards cover seamless mechanical tubing?
ASTM A519 covers seamless carbon and alloy steel mechanical tubing. Precision seamless tubes are also covered by EN 10305, DIN 2391 and GB/T 3639.
Q4. What is the difference between ASTM A513 and A519?
ASTM A513 covers electric resistance welded (ERW) mechanical tubing, including DOM T5, while ASTM A519 covers seamless mechanical tubing. Both define tolerances and properties for mechanical applications.
Q5. What is HSS structural tubing?
Hollow structural sections are structural tube produced to standards such as ASTM A500, available in round, square and rectangular shapes for buildings, bridges, towers and machinery frames.
Q6. Why are tolerances important in mechanical tubing?
Machinery components are machined from tube or assembled into systems where consistent dimensions matter. Tight OD, ID and wall tolerances reduce scrap, simplify assembly and ensure predictable performance.
Q7. What grades are commonly used for mechanical tube?
Common carbon grades include 1026 and 1010-1020 series under ASTM A513/A519, St37/St44/St52 under DIN 1629, and S235/S275/S355 designations under EN 10210/10297.
