Page 18 - ITAtube Journal 1 2023

Technical Papers
SMS group
New Piercer Concept
On the way to “No-Eccentricity”
Author: Christian Haferkamp
1 Market requirements
OCTG products follow strict tolerances; standards like API form only the minimum requirement. Even though Tubing and Casing products are not necessarily seam- less tubes, but can also be ERW-produced, often enough drilling companies do prefer seamless products. There are certainly different process technologies for the pro- duction of seamless OCTGs available, but one process step is common to all of them: Piercing.
2 Technological challenge
The seamless tube technology made several major developments steps in the past decades towards better tolerances and quality results: the 3-roll PQF® process in 2003, technological software like Carta Neo® optimizing the stretch-reducing process, or hydraulic adjustment of rolls, to name only a few.
The first forming step, which creates the hollow shell out of the billet, has often been overlooked. Modern rolling mills use a Cross Roll Piercing Mill for this first step. The design of Cross Roll Piercing Mills has been improved throughout the recent past
as well. One of the biggest challenges here is to control the eccentricity of the piercing process, as eccentricity has a direct impact on the result of the final tube. The subse- quent processes, i.e. elongation and sizing/ stretch reducing cannot correct the eccen- tricity, which has been introduced during piercing and have to cope with the results of the first process step in rolling seamless tubes.
However, controlling this parameter is not as easy as one might think. The impacting variables are manifold. Homogeneous tem- perature distribution in the hot billet, the material and mechanical properties as well as the dimensional tolerances of the billet itself are just some of the material param- eters which impact the outcome of the piercing process. But also the equipment side has to be controlled, also here multiple variables impact the outcome: Alignment
of the pass line, condition and adjustment of the rolls, guiding of the billet and hollow bloom, etc.
3 New Piercer Concept
SMS has been continuously working on improving the design of its Piercing Mill.
A dedicated design team has been devel- oping significant improvements. The improved design of the SMS piercing mill strives towards the vision of “No eccentric- ity”. The design team made improvements to some core assemblies, such as:
• Mill stand design,
• Hydraulic adjustment of the piercing rolls, and
• Diescher Disc adjustment.
The new design of the mill stand requires
ITAtube Journal May 2023
18