Sorting out the names SC conduit, welded steel pipe, galvanised steel pipe and hot-dip galvanised welded steel pipe (four dimensions: drawing designation, base-pipe process, corrosion protection, full standard name), the code requirements on galvanising (hot-dip mandatory, cold galvanising banned), and the general rule for quota attribution in installation works

Topic Positioning

In installation works the four names "SC conduit / welded steel pipe / galvanised steel pipe / hot-dip galvanised welded steel pipe" are easily confused. They are not four parallel pipes but names on four dimensions - drawing designation, base-pipe process, corrosion protection and full standard name - and the physical object falls into only two classes, "galvanised" and "non-galvanised". This card clarifies the differences, the codes' mandatory requirements on the galvanising process, and the attribution rule "fix the discipline first, then whether galvanised, finally the laying / jointing method".

Core Conclusions

1. The identity of the four names

1. Welded steel pipe - the base-pipe process name: steel pipe made by rolling and welding steel plate or strip, carrying general lower-pressure fluids (welded steel pipe for low-pressure fluid conveyance) - water, sewage, gas, air, oil and heating steam; the product standard is GB/T 3091-2008 Welded Steel Pipes for Low Pressure Fluid Conveyance (JGJ/T 191-2009 Standard for Terminology of Building Materials, 9.1.4). It is the "parent" of the galvanised pipes.
2. Galvanised steel pipe - the corrosion-protection name: welded steel pipe with a rust-proofing zinc coat applied to the pipe wall. Galvanising divides into cold galvanising and hot-dip galvanising; cold-galvanised production of welded steel pipe is now obsolete. Galvanised welded steel pipe may carry mildly corrosive fluids at low and medium pressure - water supply, gas, air, sewage and heating steam; the product standard is likewise GB/T 3091-2008 (JGJ/T 191-2009, 9.1.6).
3. Hot-dip galvanised steel pipe (hot-dip galvanised welded steel pipe) - steel pipe whose inner and outer surfaces are treated by the hot-dip galvanising process (GB/T 50680-2012 Standard for Basic Terminology of Urban Gas Engineering, 6.2.20); a compound expression of "hot-dip galvanising + welded steel pipe", stressing the hot-dip method - the same physical object as "galvanised welded steel pipe".
4. SC conduit - the habitual designation for steel conduit on electrical construction drawings, not a national-standard term; the drawing meaning follows the legend and the design notes (commonly hot-dip galvanised welded steel pipe). Quota application follows the material, galvanising and laying method fixed by the design notes - the letters "SC" carry no weight.

2. Codes mandate hot-dip galvanising and ban cold galvanising

• GB 50261-2017 Code for Construction and Acceptance of Sprinkler Systems, clause 3.2.2: galvanised steel pipes and fittings shall undergo on-site visual inspection and meet: 1 galvanised steel pipe shall be hot-dip galvanised inside and out, the zinc layer on inner and outer surfaces showing no peeling or rusting; the inner and outer diameters complying with GB/T 3091 Welded Steel Pipes for Low Pressure Fluid Conveyance or GB/T 8163 Seamless Steel Pipes for Fluid Conveyance. 2 surfaces free of cracks, shrinkage cavities, slag inclusions, folds and laps. 3 thread-sealing faces complete, undamaged and burr-free. Extent: all; method: observation and measurement. The clause commentary states plainly that hot-dip galvanising is required to align with the design code, and reminds engineers that cold-galvanised pipe is not allowed in the system.
• CJJ 127-2009 Technical Specification for Metallic Drainage Pipes in Buildings, clause 3.2.4: welded and seamless steel pipes for building drainage shall be hot-dip galvanised inside and out against corrosion, or plastic-coated where needed; cold-galvanised steel pipe must not be used. When hot-dip galvanised, the zinc layers inside and out shall be even, with no missed spots and no spatter burrs; plastic-coated pipe shall further comply with CJ/T 120 Coated Steel Pipes for Water Supply.

3. Jointing requirements for galvanised steel conduit (T/XCIA 2-2020 Technical Specification for Preventing Common Quality Defects in Housing Projects, 9.3.1)

• Metallic electrical conduit must not be butt fusion welded; galvanised steel conduit and steel conduit with wall thickness 2 mm or less must never take sleeve fusion welding - only threaded, crimp-type or set-screw connections.
• Galvanised steel conduit shall be threaded; the threaded length at the pipe end shall be not less than half the coupling length, no more than two threads exposed at each end after jointing, and the threads shall be corrosion-protected; bonding shall be via dedicated earthing clips, the wire between two clips a yellow-green copper flexible conductor of cross-section not less than 4 mm2.
• Welded steel conduit shall be joined with welded sleeves, the sleeve length 1.5 to 3 times the pipe OD, the pipe butts at the sleeve centre, the welds sound and tight - watertight as the test; at both sleeve ends a round bar of 6 mm to 8 mm diameter is welded across as the earthing bond.

4. Three keys to quota attribution: discipline first, then galvanising, finally laying / jointing

• Discipline first: electrical conduit, water supply and drainage, gas, fire protection sit in different discipline chapters; items must not cross disciplines.
• Then galvanising: laying of galvanised electrical conduit takes the galvanised steel pipe laying items; crimp-type thin-wall steel conduit (KBG) takes the sleeved set-screw galvanised electrical conduit (JDG) items (SJG 111.3-2022 Consumption Quota Standard for Urban Utility Tunnels, Volume 3 Ancillary Installation Works, conduit works notes).
• Finally the laying method, nominal-diameter band and jointing method (surface / concealed, threaded / welded) fix the concrete item. Example: Beijing DB11/T 2382-2024 Construction Works Consumption Quota Standard, Annex G, "galvanised steel pipe, surface laid, nominal diameter (mm, not exceeding) 40", item G3-13-9, unit m, work content: positioning, marking, drilling, embedding bolts, sawing, threading, bending, pipe fitting, earthing etc.
• Companion position: the conduit items assume co-ordination between disciplines and exclude chases, grooves, holes and making good (SJG 111.3-2022); "galvanised electrical conduit" carries no separate item for its name - it still takes the galvanised steel pipe laying items.

Applicability Boundaries

• "Galvanised / non-galvanised" follows the design notes and the product standards; cold-galvanised pipe is not allowed in water supply, drainage, fire and gas systems with corrosion-protection requirements and must not serve as a pricing or procurement basis.
• The attribution rule is exemplified by the concrete items of Beijing DB11/T 2382-2024 and Shenzhen SJG 111.3-2022; other regions / sectors follow the chapter notes and itemisation of their current consumption standards or quotas - item codes must not be transplanted across regions.
• Electrical conduit (SC / galvanised steel conduit) and water-supply, drainage and gas piping sit in different discipline volumes with different jointing requirements and measurement rules and must not be mixed.
• This card carries no unit rates or consumption values; actual pricing follows the quota of the applicable period and the published market price information.

Further Reading

• Term definitions: JGJ/T 191-2009 Standard for Terminology of Building Materials, 9.1.4 and 9.1.6; GB/T 50680-2012 Standard for Basic Terminology of Urban Gas Engineering, 6.2.20.
• Product standards: GB/T 3091-2008 Welded Steel Pipes for Low Pressure Fluid Conveyance; GB/T 8163 Seamless Steel Pipes for Fluid Conveyance; CJ/T 120 Coated Steel Pipes for Water Supply.
• Construction and acceptance: GB 50261-2017 Code for Construction and Acceptance of Sprinkler Systems, clause 3.2.2 and commentary; CJJ 127-2009 Technical Specification for Metallic Drainage Pipes in Buildings, clause 3.2.4; T/XCIA 2-2020, clause 9.3.1.
• Quota and measurement: SJG 111.3-2022, clause 2.1.19 conduit works notes; Beijing DB11/T 2382-2024, Annex G, item G3-13-9; the measurement split of electrical conduit / cable tray / trunking per GB/T 50856-2024 Measurement Code for General Building Services Works.