Seamless pipes have, since the early twentieth century, been among the most vital infrastructural components of heavy industries. The production of these pipes—known in Iran as “Mannesmann”—was a direct response to the need for safely transporting fluids under high pressure and temperature—needs that welded pipes, due to the inherent weakness of the weld seam, could not fully satisfy. Accordingly, the development of rotary piercing and continuous rolling technologies paved the way for manufacturing an integral, homogeneous product; by eliminating metallurgical discontinuities in the wall, it maximizes mechanical and chemical resistance while minimizing the risks of leakage or thermal cracking.
Historical transformation and the role of technology in the evolution of seamless pipe
After the first trial productions in the late 1880s, it quickly became clear that the Mannesmann method—by delivering significant weight savings and dramatically extending service life for piping systems—could transform traditional approaches to process-unit design. The maturation of Pilger Rolling and, later, sequential three-roll mills not only increased production efficiency but also made it possible to manufacture pipes in larger diameters and variable wall thicknesses. In parallel, cold drawing and hot extrusion were developed to achieve better dimensional accuracy and surface finish—factors that are decisive in precision-instrument industries and high-pressure power-plant structures.
From billet to pipe: the production route
- Billet cutting and controlled preheating: After inspection, carbon or stainless-steel billets are cut to length based on the target diameter and preheated in a furnace to 1200–1250 °C to condition the crystal structure for plastic deformation.
- Rotary piercing: A rotating conical piercer, under high axial force and torque, penetrates the billet center to form the initial cavity; this step is essential to create the “hollow shell” that becomes the pipe.
- Rolling the hollow section: The hollow shell passes through mandrel-mill stands so that the OD and wall thickness are reduced over multiple passes to approach nominal dimensions.
- Straightening and sizing: To equalize wall thickness, the semi-finished pipe is subjected to axial tension in reducing/sizing stands or cold drawing; this step corrects ovality and surface irregularities.
- Cut-to-length, heat treatment, and pressure testing: Pipes are cut into standard 6 or 12 m lengths, then normalized or tempered to relieve residual stresses. Finally, hydrostatic testing and non-destructive tests (ultrasonic and eddy-current) ensure metallurgical homogeneity and the absence of microcracks.
Key features and technical advantages
- Mechanical stability: The absence of a weld seam equalizes stress distribution and enables withstanding pressure surges up to twice the design pressure—a key factor in sour-gas lines and ultra-supercritical boilers.
- Thermal resistance: A uniform ferrite–pearlite structure or stabilized austenitic stainless steel ensures dimensional stability from −100 to 650 °C.
- Excellent corrosion behavior: Low-carbon microalloyed steels and grades such as 316L, 321, and super duplex deliver strong resistance in hydrochloric acid, hydrogen sulfide, and seawater environments.
- Low friction coefficient: A smooth, scale-free inner surface reduces line pressure drop and increases pumping capacity—an economic advantage in long light-oil pipelines.
- Ease of machining and bending: Homogeneous grain structure without discontinuities improves weldability and formability and reduces the need for high preheat.
Table 1 – Common Mannesmann pipe schedules and approximate working pressures
Schedule (SCH) — Wall thickness range (mm) — Nominal diameter (in) — Approx. design pressure for carbon steel at 20 °C (bar)
20 — 2–6 — ½–12 — 25–40
40 — 2.8–10 — ½–12 — 50–90
60 — 4–12 — 8–24 — 75–120
80 — 3.2–12.7 — ½–24 — 100–170
120 — 6–20 — 4–24 — 150–250
160 — 7–30 — 2–24 — 200–320
Taxonomy by base metal and alloy
- Microalloyed carbon steel (A106, A53 Type S): Cost-effective for refineries and water-steam transfer lines at medium pressure; max service temperature 425 °C.
- Austenitic stainless (304/304L, 316/316L): Suitable for food industry, cryogenic equipment, and chloride environments; higher Ni and Mo enhance pitting resistance.
- Super duplex (S32750, S32760): Mixed ferritic–austenitic phases with high Cr/Mo ratio ensure safety in H₂S-containing environments.
- Cr-Mo alloy steel (T11, P22): Withstands >500 °C; suitable for power-plant heat exchangers.
Table 2 – Comparison of key properties of three common families
Key property — Carbon steel Class B — 316L stainless steel — Super duplex S32750
Max design pressure (bar) — 170 (SCH 80) — 160 (SCH 80) — 200 (SCH 80)
Operating temperature range (°C) — −29 to 425 — −196 to 550 — −50 to 315
Pitting corrosion resistance — Medium — High — Very high
Fracture toughness below zero — Medium — Excellent — Excellent
Weldability — Very good — Excellent — Good
Relative cost — Low — Medium — High
Application areas
- Upstream oil & gas: Drill strings, well flowlines, and subsea manifolds, resisting up to 10,000 psi and H₂S presence.
- Petrochemical & refining: Hydrogen reformer furnaces, steam-cracking reactors, and air-cooler exchangers subject to continuous thermal cycling.
- Combined-cycle & ultra-supercritical power: Boiler, superheater, and reheater tubes reaching 600 °C.
- Food & pharma: Sterile CIP-SIP piping with 0.8 µm Ra surface finish to prevent bacterial buildup.
- High-pressure hydraulics: Shafts and cylinders of industrial jacks working up to 350 bar.
- Negative-pressure and vacuum systems: Transfer lines for liquid nitrogen and deep-cryogenic helium down to −269 °C.
Joining techniques and quality control
- Weld-area preheat: 100–150 °C for carbon steel; 200–250 °C for HAZ-cracking-sensitive alloys like super duplex.
- GTAW root + SMAW/FCAW fill: Ensures full penetration with restrained heat input.
- Post-weld heat treatment (PWHT): For Cr-Mo alloys per ASME IX, 650 °C for 1 h per 25 mm of thickness.
- Helium leak test: For vacuum and hydrogen systems, sensitivity to 10⁻⁶ mbar·L/s.
Economic factors affecting final price
- Slab-to-OD ratio: Larger pipes mean more cutting scrap and higher cost.
- Base-metal grade and alloying additions (e.g., Ni, Mo) tied to global commodity markets.
- Wall thickness and multi-stage heat treatment increase energy consumption.
- Supplementary tests such as PMI and full-body UT for offshore projects.
Key selection and purchasing tips
- Always match design pressure/temperature with schedule and grade to avoid over-spending or under-strength.
- For chloride- or CO₂-bearing environments, choose a PREN > 32 to reduce pitting risk.
- If on-site cold bending is needed, Schedule 40 below 4 in offers the best balance of flexibility and strength.
- Request heat number, EN-10204/3.2 certificate, and hydrotest results from the seller; these ensure full material traceability.
The place of “Tamam Baha” in the supply chain
With a focus on specialized distribution of seamless products in Schedules 20–160, Tamam Baha offers a broad portfolio of domestic and imported makes for oil, gas, and power industries. Its competitive edge combines up-to-date inventory with precision cutting, certificates of authenticity, and rapid delivery for time-critical projects. While Tamam Baha is not the only supplier in Iran, its engineering know-how and transparent pricing make it a dependable choice for owners and contractors across Iran and neighboring markets.
