Tenaris designs mother pipes on a case by case basis depending on the applicable standard and the type of bend the customer requires in terms of angle, radii, wall thickness after bending etc.

When our technicians are designing the mother pipe the most important factors are:

	The Pipe Manufacturing Process
	Dimensional Tolerances
	Chemical Composition

Production of a high quality bend depends very much upon the manufacturing process of the pipe that will eventually be transformed into the bend. Thinning inevitably occurs on the extrados of the bend during the heat induction bending process and therefore getting the wall thickness, mechanical and chemical properties of the pipe right during the manufacturing stage is essential. Special settings are used during both the rolling and heat treatment processes, which combined with Tenaris metallurgical experience, ensures that the mother pipe meets the requirements.

Tenaris shares with the bender information related to the manufacturing process of the mother pipe in order to allow them to select the best bending conditions ( bend cycle, temperatures, cooling rates etc.).

Chemical Composition

Getting the chemical composition of the mother pipe just right also helps to recover the material's properties after the heat induction bending process has taken place.
For example a higher carbon (CE) equivalent enhances the quenching stage of the bending process. However Tenaris metallurgists must strike a balance with the chemical content so as not to make the bend unsuitable for welding. In such cases Tenaris can add Niobium (which also positively effects grain refinement) and keep the CE content at an acceptable level for welding.

Depending on pipe dimensions, grades and final bending conditions (quenched & tempered, normalized etc.), other alloying elements such as Mo and V or even Ni and Cr are added to the steel in order to guarantee the required hardenability and mechanical properties.

Dimensional Tolerances

The dimensional tolerances of the mother pipe are of paramount importance for obtaining the correct dimensions on the bend.
Tenaris makes sure that the bend has at least the minimum WT of the mother pipe. This is guaranteed by working with restricted WT tolerances on the mother pipe or increasing its WT (taking into account typical thinning outcomes of the bending process). Tenaris also avoids as much as possible the internal or external misalignment between the tangent of the bend and the mother pipe.