Round Steel Pipes (CHS)
ERW, galvanized and seamless round pipe from ½″ to 12″ nominal bore (21.3–323.9 mm OD) — manufactured in Dammam to ASTM A53, API 5L, EN 10219 and EN 10255 for structures, water, scaffolding and line service.
Standards
ASTM A53 / API 5LEN 10219 · EN 10255 · A106
Diameter
½″ – 12″ NB21.3 – 323.9 mm OD (custom on request)
Finish
Black / GalvMill, pre-galv, hot-dip, primed, 3LPE
Lead time
1–2 weeksStock items · custom 3–6 wks
What is a round steel pipe?
A round pipe — or circular hollow section (CHS) — is a closed tube with a circular cross-section and a uniform wall thickness. Because steel is distributed evenly around the centre, the section behaves identically no matter which way the load arrives, and it resists twisting better than any other shape of the same weight.
That symmetry makes round pipe the natural choice for columns and props, for handrails, scaffolding and architectural frames, and for carrying water, gas and other fluids — where the circular bore gives the smoothest flow and the lowest friction.
Rouad Steel produces round pipe on high-speed ERW lines: steel strip is roll-formed into a cylinder, high-frequency welded along the seam, then sized and straightened to a precise outside diameter. Galvanized, primed and seamless options are available where service conditions demand them.
Mill test certificates (EN 10204 3.1) accompany every batch, covering chemical composition, mechanical properties, hydrostatic test and dimensional tolerances.
Why engineers choose round pipe
One shape, the same strength in every direction — efficient in compression, unbeaten in torsion and the cleanest path for flow.
Equal strength all round
A symmetric section has the same radius of gyration about every axis, so it carries load identically from any direction — the ideal column and prop.
Best in torsion
The closed circular profile has the highest torsional constant of any section per kilo — first choice for shafts, masts and members that twist.
Smoothest flow
A circular bore gives the lowest friction and the most even pressure for water, gas and fluid lines — and the smallest wind and wave load when exposed.
Corrosion options
Pre-galvanized, hot-dip galvanized, primed and 3LPE/3LPP coatings extend service life in buried, marine and humid environments.
Clean architectural look
The continuous curved surface suits exposed steelwork, balustrades, canopies and façades with minimal edges to finish.
Predictable tolerances
Tight control on outside diameter, wall, straightness and roundness for repeatable, drama-free fit-up and reliable couplings.
NB, OD & schedule — read a pipe size right
Round pipe is described by three numbers. Get them right and every fitting, flange and coupling lines up the first time.
Nominal bore
The name of the size (e.g. 2″ / 50 NB). Roughly the inside diameter — used to call up the pipe and its fittings.
Outside diameter
The fixed outer dimension for each NB. It never changes with wall, so threads, couplings and flanges always fit.
Schedule / wall
The wall thickness (SCH 40, SCH 80…). A higher schedule means a thicker wall, smaller bore and higher pressure rating.
Rule of thumb: the OD stays the same across every schedule of one NB — only the wall grows inward. So SCH 80 has the same outside size as SCH 40 but a thicker wall and a narrower bore.
Round pipe vs square & rectangular tube
All three are hollow sections from the same grades and standards — the cross-section decides where each one wins.
A side-by-side comparison to help you specify the right section for your load case.
→ scroll table| Feature | Round pipe (CHS) | Square / rect. tube (SHS / RHS) |
|---|---|---|
| Cross-section | Circular — symmetric | Four flat sides |
| Strength axis | Equal in every direction | Strong about its faces / long axis |
| Torsion (twisting) | Best — highest per kilo | Good, lower than round |
| Fluid flow | Smoothest, lowest friction | Not used for flow |
| Best for | Columns, props, masts, fluid & scaffold | Bolted frames, beams, flush connections |
| Connections | Couplings, threads, saddle welds | Flat faces — easy to bolt & weld |
| Exposed loads | Low wind & wave drag | Higher drag, flat faces catch wind |
| Standards & grades | A53 / API 5L / EN 10219 · S235–S355 | EN 10219 / 10210 · S235 / S355 |
Rule of thumb: choose round (CHS) when load can arrive from any direction, when the member twists, or when it carries fluid; choose box sections when you need flat faces to bolt and connect. Not sure? Talk to our technical desk.
ERW, galvanized & seamless round pipe
ERW & structural CHS
Electric-resistance-welded round pipe — roll-formed and HF-welded at ambient temperature. The economical workhorse for water, structural and general line service.
- ASTM A53 · EN 10219 · S235/S355
- Consistent OD & wall, hydro-tested
- Best value for volume orders
Galvanized round pipe
Pre-galvanized strip or hot-dip galvanized after manufacture for ready corrosion resistance — the standard for water, scaffolding, fencing and outdoor frames.
- EN 10255 / ASTM A53 · BS 1387
- Pre-galv & hot-dip options
- Threaded & socketed on request
Seamless & line pipe
No weld seam for high-pressure, high-temperature and critical service — plus API 5L line pipe for oil, gas and water transmission.
- ASTM A106 · API 5L Gr B–X65
- Beveled ends, 3LPE/3LPP coating
- High-pressure & sour service
Round pipe sizes & weights — NB / OD / schedule
Nominal mass per metre for carbon-steel round pipe to ASME B36.10 (SCH 40 & SCH 80). Other walls, schedules and grades available — ask our team.
→ scroll table| Nominal bore | OD (mm) | SCH 40 wall | SCH 40 kg/m | SCH 80 wall | SCH 80 kg/m |
|---|---|---|---|---|---|
| Small bore · ½″ – 1½″ | |||||
| ½″ (15 NB) | 21.3 | 2.77 | 1.27 | 3.73 | 1.62 |
| ¾″ (20 NB) | 26.7 | 2.87 | 1.69 | 3.91 | 2.20 |
| 1″ (25 NB) | 33.4 | 3.38 | 2.50 | 4.55 | 3.24 |
| 1¼″ (32 NB) | 42.2 | 3.56 | 3.39 | 4.85 | 4.47 |
| 1½″ (40 NB) | 48.3 | 3.68 | 4.05 | 5.08 | 5.41 |
| Medium bore · 2″ – 4″ | |||||
| 2″ (50 NB) | 60.3 | 3.91 | 5.44 | 5.54 | 7.48 |
| 2½″ (65 NB) | 73.0 | 5.16 | 8.63 | 7.01 | 11.41 |
| 3″ (80 NB) | 88.9 | 5.49 | 11.29 | 7.62 | 15.27 |
| 4″ (100 NB) | 114.3 | 6.02 | 16.08 | 8.56 | 22.32 |
| Large bore · 5″ – 12″ | |||||
| 5″ (125 NB) | 141.3 | 6.55 | 21.77 | 9.52 | 30.97 |
| 6″ (150 NB) | 168.3 | 7.11 | 28.26 | 10.97 | 42.56 |
| 8″ (200 NB) | 219.1 | 8.18 | 42.55 | 12.70 | 64.64 |
| 10″ (250 NB) | 273.1 | 9.27 | 60.31 | 12.70 | 81.55 |
| 12″ (300 NB) | 323.9 | 10.31 | 79.73 | 12.70 | 97.46 |
Weights are indicative and rounded; walls in mm. OD is fixed per NB across all schedules. SCH 40 = "standard", SCH 80 = "extra-strong" for most sizes. Need SCH 10/20/160, XXS, a stock list or a size not shown? Contact our sales desk.
How to choose the right round pipe
Four quick checks that get you to the correct size — share these with your quote and we will confirm the rest.
Define the duty
Is it structural (a column or prop), fluid-carrying (water, gas) or general (scaffold, fence, frame)? The duty sets the standard and grade.
Pick the diameter (NB / OD)
For structure, larger OD adds stiffness and capacity. For flow, choose NB for the required throughput, allowing for friction loss along the run.
Set the schedule / wall
SCH 40 suits general and low-to-medium pressure; SCH 80 or higher for higher pressure, structural load or a corrosion allowance.
Choose grade & finish
A53/API 5L or S235/S355 to suit the duty; add pre-galv, hot-dip or 3LPE for buried, marine and outdoor service. Specify the standard.
Where round pipe is used
From load-bearing columns to water mains, round pipe is the section of choice wherever strength must work in every direction — or fluid must flow.
- Columns, props & bracing
- Water, gas & fluid pipelines
- Scaffolding & access towers
- Handrails, balustrades & barriers
- Fencing, gates & bollards
- Lighting, sign & flag poles / masts
- Fire-fighting & sprinkler lines
- Boreholes, casings & piling
- Canopies, trusses & space frames
- Carports, pergolas & shade structures
- Greenhouse & agricultural frames
- Furniture, gym & playground equipment
Need round pipe for a project?
Send us your cutting list or BOQ — we reply with pricing, weights and mill test certificates within 24 hours.
Specifications we manufacture to
| Standard | Type | Common grades | Notes |
|---|---|---|---|
| ASTM A53 | ERW / seamless | Gr A, Gr B | Structural & general line pipe |
| API 5L | ERW / seamless | Gr B, X42–X65 | Oil, gas & water transmission |
| EN 10219 | Cold-formed CHS | S235JRH, S355J2H | Structural round hollow section |
| EN 10255 | ERW (BS 1387) | — | Water & screwed/socketed pipe |
| ASTM A106 | Seamless | Gr B, Gr C | High-temp / high-pressure · on request |