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Surplus Pipes, Tubes & Fittings: Grades, Schedules & MTC
Piping represents a substantial portion of the capital cost in process plants, petrochemical refineries, power generation boilers, and HVAC infrastructure. When a refinery expansion or cross-country pipeline project concludes, contractors are regularly left with thousands of meters of unused line pipes, direct boiler tubes, and palletized fittings (elbows, tees, reducers, flanges).
Purchasing stock lots in pipes, tubes, and fittings offers massive procurement savings. However, piping systems handle volatile hydrocarbons, high-pressure steam, and corrosive acids. Installing an unverified pipe or a mislabelled secondary fitting can cause rupture, explosion, or catastrophic plant shutdown.
Here is what procurement engineers and surplus traders must inspect before paying for excess pipe and fitting stock lots in India.
1. direct vs Welded (ERW / SAW): Dimensional Checks
The manufacturing method determines pressure ratings and application suitability:
- direct Pipes (ASTM A106 Gr B / ASTM A53 Gr B): Extruded from solid steel billets with zero longitudinal weld seam. Used for high-pressure steam, power boilers, and oil pipelines.
- ERW (Electric Resistance Welded - IS 1239 / IS 3589): Formed from steel coil strips with a high-frequency resistance weld seam along the length. Common in general plumbing, structural framing, and low-pressure firefighting networks.
- LSAW / HSAW (Submerged Arc Welded): Large diameter line pipes (16 inches to 100+ inches) used for cross-country water supply and municipal utility lines.
Verification of Wall Thickness and Schedule
Never rely solely on nominal pipe size (NPS). Always measure wall thickness with a calibrated ultrasonic thickness gauge or vernier micrometer across four radial quadrants.
- Pipe Schedules: Compare wall thickness against standard ASME B36.10M tables (Sch 10, Sch 20, Sch 40/STD, Sch 80/XS, Sch 160, XXS).
- Secondary / Commercial Pipe Alert: Many secondary mills sell pipes under nominal weights with -15% to -20% negative wall thickness tolerances. Under ASME/ASTM standards, permissible negative wall thickness tolerance is strictly capped at -12.5%. Anything thinner is secondary structural tube, not pressure piping.
2. Pipe Fittings: Forged vs Butt-Weld
Surplus fittings lots include forged high-pressure fittings (threaded / socket-weld) and butt-welding fittings.
| Fitting Type | Standard Specification | Common Pressure Classes | Key Inspection Points |
|---|---|---|---|
| Butt-Weld Elbows & Tees | ASME B16.9 / ASTM A234 WPB | Matched to Pipe Schedule (Sch 40, Sch 80) | Bevel angle (37.5° ±2.5°), wall thinning at the crotch |
| Forged High-Pressure Fittings | ASME B16.11 / ASTM A105 | Class 2000, 3000, 6000, 9000 | Thread profile (NPT vs BSPT), socket depth |
| Pipe Flanges (WNRF, SORF, Blind) | ASME B16.5 / ASTM A105 | Class 150, 300, 600, 900, 1500 | Serration spiral depth (125-250 AARH), bolt circle pitch |
The Crotch Thinning Check
When butt-weld elbows are manufactured by hot extrusion or cold mandrel drawing, the outer curve of the bend (extrados) and the inner crotch (intrados) experience wall thinning. Measure the wall thickness at the center of the bend to ensure it has not thinned below the minimum specified schedule thickness.
3. The Mill Test Certificate (MTC) and Heat Traceability
In structural and pressure piping, physical steel without a verifiable Mill Test Certificate (MTC) is legally classified as "untested commercial pipe" and is worth only 50% of certified prime line pipe.
The Traceability Chain: EN 10204 3.1
Every prime pipe has a continuous dot-matrix stencil or hard stamp along its length displaying: ``` MANUFACTURER NAME • ASTM A106 GR.B • 4" SCH 40 SMLS • HEAT NO. 74829 • LOT NO. 1102 • MADE IN INDIA ```
- Heat Number Matching: The heat number stamped on the pipe body must match the heat number printed on the original manufacturer's Type 3.1 inspection certificate under EN 10204.
- Chemical Composition: Check carbon equivalent (CE) value, sulphur content (max 0.035%), and phosphorus levels.
- Mechanical Testing: Verify yield strength ($R_{eH} \ge 240\text{ MPa}$), ultimate tensile strength ($R_m \ge 415\text{ MPa}$), and elongation percentage.
If you suspect material substitution (e.g., carbon steel painted to mimic alloy steel P11/P22), request a portable Positive Material Identification (PMI) XRF spectrometer scan before payment.
4. Packing, Bevel Protection, and Weight Verification
- Bevel End Protectors: Bevelled pipe ends ($37.5^\circ$ angle for butt welding) must be protected by plastic or metal bevel caps. If uncapped pipes bump together during rough road transit, the feather edges get dented, requiring costly re-bevelling on site.
- Weighment Verification: Calculate theoretical weight using the standard engineering formula:
$$W = 0.02466 \times (D - t) \times t$$ (where $W$ is weight in kg/m, $D$ is outside diameter in mm, and $t$ is wall thickness in mm). Compare the theoretical weight against the certified weighbridge slip to detect negative tolerance rolling.
Use the free Bikwao calculation tools to convert weights, pipe dimensions, and verify tax billing splits. You can also source specific pipe schedules or clear surplus godown lots across India on the Bikwao requirements board.
Questions
What is the difference between ASTM A106 and ASTM A53 pipes?
ASTM A106 is exclusively for direct carbon steel pipe intended for high-temperature service (such as steam lines and process piping up to 430°C). ASTM A53 covers both direct and welded steel pipe intended for general structural, low-pressure plumbing, and air utility applications.
How do I store surplus steel pipes to prevent internal rust?
Pipes should be stored with a slight tilt on timber dunnage to allow internal condensation and rainwater to drain freely. Never store pipes directly on bare soil. For long storage periods, apply a bituminous varnish or water-based rust-inhibiting coating to the outer and inner surfaces.
What is the GST rate on steel pipes and pipe fittings?
Iron and steel pipes and tubes fall under HSN Chapter 7304 (direct), 7305, and 7306 (welded), attracting 18% GST. Pipe fittings (flanges, elbows, tees) fall under HSN 7307, also attracting 18% GST.
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