This article explains the main differences existing between “Forged Pipes” vs “Seamless Pipes” and the reasons why forged pipes may have advantages over standard seamless pipes in heavy duty applications that require enhanced chemical and mechanical properties (example: fluids conveyance within nuclear power plants) or in specific circumnstances.
What is a Forged Pipe?
A forged pipe (or a forging in general) is manufactured by:
- heating a steel ingot above its deformation temperature, a value that depends upon the material grade (for instance, the deformation temperature of carbon steel is above 600 degrees C°), and
- shaping the ingot under a forging press with a compression force, and
- applying CNC machining to the roughly formed shape coming out out the press to achieve the final form and the given tolerances
Forged products of any material grade can be manufactured, and the production flow is represented in the picture below:
The production process is itemized (the mill produces just one pipe at a time) and it is mainly oriented to special sizes or applications and heavy components. The final CNC machining allows to produce with precise tolerances (starting from -0/+1 mm on each dimension). The picture below represents a forging press of approximately 12.000 tons:
What is a Seamless Pipe?
Differently from a forged pipe, which is produced as described above, a seamless pipe is produced starting from a heated steel bar, laminating it on a piercer and rolling it in a mandrel mill. This process applies for carbon steel grades (that represent the most used material grade for seamless pipes) and it’s called Mannesmann process (based on the name of its Inventor).
The production process of seamless pipes is fully automated and mainly oriented to standard sizes and large quantities (an order could go from minimum quantity of 20 pipes to a pipeline order with 5.000 km / 450 pipes of the same size). Pipes are not mechanically CNC machined except for the ends (pipe ends are beveled or threaded to allow connection of each pipe).
Sizes of Forged vs. Seamless Pipes
The size of a forged pipe is defined by:
- Outside diameter (OD)
- Inside Diameter (ID)
Forged pipes are also called “ID controlled” or “Minimum Wall Thickness Pipes” (as a min thickness is granted).
Instead, the size of a seamless pipe is defined by:
- Outside Diameter
- Wall Thickness (WT)
Seamless pipes are also called “OD controlled pipes” or “Average Wall Thickness Pipes”.
The theoretical size of each pipe is different from the actual one (due to limitations in production, and the international norms allow some dimensional tolerances).
For example, in a OD controlled size OD711 mm x WT 50 mm, the actual ID might show a 25 mm difference from ordered (= theoretical) one.
This size difference (actual vs. theoretical) might generate unexpected cost and delays during installation at site. This due to the fact, for instance, that the welding of two pipes with different ID might require longer time or extra machining of pipe ends (that were not accounted for during the pipe work engineering process).
Imperfect welding might be very critical in offshore applications or for pipes installed within a power plant (as high temperature steam might generate unwanted vortex movements, cavitation and creep problems to all the ancillary utilities existing in the plant).
Differences in Dimensional Range
Theoretically, a forged pipe could be produced in any desired size. The question is: when is it better to source forged vs. seamless pipes?
In general, forged pipes are more cost-efficient, compared to seamless pipes, in the following cases and applications:
- Larger OD (outside diameter): forged pipes show an overall cost advantage for larger OD pipes, say OD > 18” as a rule of thumb
- Heavier wall thickness pipes: forged pipes are the elective the choice for applications that require heavy wall thickness pipes, example from 40/50 mm WT upwards
- Special Dimensional Tolerance or Surface Finishing: due to its fine manufacturing process, forged pipes can be produced to custom dimensions and precise tolerances (whereas, as explained above, seamless pipes show a constant divergence between actual vs. theoretical sizes)
- Small lots (due to the fact that the minimum order size for a forged mill is just 1 pipe, whereas seamless pipes manufactures have minimum lot quantities of several tons, generally above 10)
On the contrary, Seamless Pipes are more cost-efficient in the following cases:
- OD: standard sizes from 12,7 mm (1/2″) to 457 mm (18″)
- Project requires pipes with standard wall thickness, example below 25/30 mm
- Large lots: minimum order is 200 meters / 20 pipes per size
The image below shows the competitive range for forged pipes (vs. seamless pipes) in terms of pipe OD (outside diameter) and WT (wall thickness):
What are the Typical Applications?
Heavy wall thickness pipes are mainly used in demanding applications like
- Power Generation
- Nuclear power plants
- Offshore installations
- Upstream Developments.
Power Generation steam lines, for instance, require high chrome content (alloy grade 11, grade 22, grade 91, grade 92) and heavy wall thickness lines to resist to the high temperatures generated by the energy production process.
A controlled ID Diameter pipe allows better dimensioning during the engineering stage, reduce welding costs during pipes installation, and furthermore reduce vortex fluid movements & creep risks inside the piping of the plant.
Offshore parts subject to High Mechanical Stress like Risers, J-Lay Collars, Spool Pieces are supplied in X grades (X60/X70).
Those parts require high mechanical properties, in particular very high tensile strength at low temperatures (example: an expected crush with the offshore pipeline could create serious damages to the pipelines) and requires very strict machining tolerances (example: pipelines need to be clean with pigs on routine basis).
Another common application of forged pipes is for OCTG Couplings in Upstream applications (example: couplings for OCTG casing pipes like size 18 5/8”) for heavy dimensions & heavy thickness that cannot be produced by using the standard seamless production process.
Forged J-Lay Collars
Forged Spool Pieces
Some examples of forged steel products for application in the oil & gas, power generation, and heavy manufacturing industries
Key Manufacturers of Forged Pipes
The market for forged pipes is a niche segment of the larger pipes market and is populated by a large number of small/medium size manufacturers.
The world’s most qualified forgings mills are located in Northern Italy (more than 20 suppliers) and Germany, along with some smaller production sites in China.
Please contact us in case you need recommendations based on steel grade, size, and pipe weight.
For Seamless Pipes, we have identified 2 categories of manufacturers (depending on steel grade family):
- Carbon steel pipes: global supply is dominated by global groups as Tenaris + Vallourec + Sumitomo, while Chinese manufacturers are playing a smaller role. Markets like USA or Saudi Arabia or Russia see strong presence of local suppliers, with sales limited to their local markets
- Stainless Steel pipes: European manufacturers (Salzgitter DMV / Tubacex /Sandvik) are sharing the market with growing Chinese competition
Material Grades Forged vs. Seamless Pipes
The table below shows the most common material grades of seamless pipes and their forged equivalent:
|MATERIAL TYPE||SMLS PIPE GRADE||FORGED GRADE|
|CS - Carbon Steel - High Temperature||ASTM A106 gr B / A53 gr B / API 5L gr B/X42 PSL1||ASTM A105|
|CS - Carbon - Low Temperature||ASTM A 333 gr 6||ASTM A350LF2|
|CS - Carbon Steel||API 5L gr B / X42 PSL1|
|CS - Carbon Steel||API 5L gr B / X42 PSL2||A694 F42|
|CS - Carbon Steel||API 5L gr X42 PSL2|
|CS - Carbon Steel||API 5L gr X52 PSL1|
|CS - Carbon Steel||API 5L gr X52 PSL2||ASTM A694 F52|
|CS - Carbon Steel||API 5L gr X65 PSL1|
|CS - Carbon Steel||API 5L gr X65 PSL2||A694 F65|
|CS - Carbon Steel - Galvanized||ASTM A 53 gr. B||ASTM A105|
|AS - Alloy||ASTM A 335 P11||ASTM A182 F11|
|AS - Alloy||ASTM A 335 P22||ASTM A182 F22|
|AS - Alloy||ASTM A 335 P5||ASTM A182 F5|
|AS - Alloy||ASTM A 335 P9||ASTM A182 F9|
|AS - Alloy||ASTM A 335 P91||ASTM A182 F91|
|SS - Stainless||ASTM A 312 TP304-304L||ASTM A182 F304-F304L|
|SS - Stainless||ASTM A 312 TP316-316L||ASTM A182 F316-F316L|
|SS - Stainless||ASTM A 312 TP321||ASTM A182 F321|
|SS - Duplex 22||ASTM A790 UNS S31803||ASTM A182 F51|
|SS - Superduplex 25||ASTM A790 UNS S32750 / 32760||ASTM A182 F53 / F55|
|SS - Inconel - Nichel Alloy 6625||ASTM B444 UNS N06625||ASTM B564 UNS N06625|
|SS - Inconel - Nichel Alloy 8825||ASTM B423 UNS N08825||ASTM B564 UNS N08825|
|CUNI - Cupronickel (CuNi 90/10)||ASTM B466 UNS C70600||UNS C70600|
|CUNI - Cupronickel (CuNi 70/30)|