What do the Yellow, Blue, and Red colour bands indicate on MS pipes?

They indicate the pipe class: Yellow for Light, Blue for Medium, and Red for Heavy thickness.

What is the standard hydraulic test pressure required for IS 1239 pipes?

Every tube must withstand a hydraulic pressure of 5 MPa (approx. 50 bar) without showing any signs of leakage.

What is the difference between Nominal Bore (NB) and Outer Diameter (OD)?

NB is the approximate internal bore size used for designation. The actual Outer Diameter (OD) is strictly specified in Tables 2 to 4 and is significantly larger than the NB.

IS 1239 Part 1

: 2004

Mild steel tubes, tubulars and other wrought steel fittings - Part 1: Mild steel tubes

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This standard specifies the requirements for welded and seamless plain end or screwed and socketed mild steel tubes used for water, non-hazardous gas, air, and steam. It classifies steel tubes into Light, Medium, and Heavy grades based on thickness and mass.

Specifies requirements for plain and galvanized mild steel tubes for water, gas, steam, and air.

Quick Reference Values

Hydraulic test pressure5 MPa (approx. 50 kgf/cm²)

Tolerance on thickness (Light tubes)+ Not limited, -8 percent

Tolerance on thickness (Medium and Heavy tubes)+ Not limited, -10 percent

Tolerance on mass (Single tube, Medium/Heavy)± 10 percent

Minimum mass of zinc coating (if galvanized as per IS 4736)360 g/m²

Standard random length of tubes4 to 7 meters

Practical Notes

Pipes are commonly identified at the site by painted colour bands: Yellow for Light (Class A), Blue for Medium (Class B), and Red for Heavy (Class C).

Medium and Heavy class tubes are generally recommended for underground laying or high-pressure plumbing to ensure adequate durability and corrosion allowance.

For potable water supply, always ensure tubes are Hot-Dip Galvanized (GI) according to IS 4736, as ungalvanized 'black' tubes will quickly rust.