CLAIMS
1. A method for classifying a metal tube having a total length (Ltot), wherein there are provided a detection system for detecting the eccentricity of a tube, adapted to measure the eccentricity of the tube along its entire length (Ltot), a relative movement being provided between the tube and the detection system, and a processor adapted to process data obtained from said detection system, in said method being defined:
- a first eccentricity threshold (S1),
- a first reference length (L1) correlated to said first eccentricity threshold (S1), the method comprising the steps of:

a) measuring the eccentricity of the tube along the entire total length (Ltot), by means of the detection system, during said relative movement,
b) executing a first sum of lengths of tube portions having eccentricity either higher than or equal to the first eccentricity threshold (S1) by means of the processor,
c) assigning a first class to the tube if the value of said first sum is lower than said first reference length (L1), otherwise assigning a second class to the tube.
2. A method according to claim 1, wherein a second eccentricity threshold (S2),
higher than the first eccentricity threshold (S1), and a second reference length
(L2), correlated to said second eccentricity threshold (S2), are defined,
wherein in step b) a second sum of lengths of tube portions having eccentricity either higher than or equal to the second eccentricity threshold (S2) is also executed,
and in step c) a third class is assigned to the tube if the value of said second sum is either higher than or equal to said second reference length (L2), otherwise said second class is assigned to the tube if the value of said first sum is either higher than or equal to said first reference length (L1), otherwise the first class is assigned to the tube.
3. A method according to claim 2, wherein a third eccentricity threshold (S3),
higher than the second eccentricity threshold (S2), and a third reference length
(L3), correlated to said third eccentricity threshold (S3), are defined,
whereby in step b) a third sum of lengths of tube portions having eccentricity either higher than or equal to the third eccentricity threshold (S3) is also executed,

and in step c) a fourth class is assigned to the tube if the vaiue of said third sum is either higher than or equal to said third reference length (L3), otherwise said third ciass is assigned to the tube if the vaiue of said second sum is either higher than or equal to said second reference length (L2), otherwise said second class is assigned to the tube if the vaiue of said first sum is either higher than or equal to said first reference length (L1), otherwise the first class is assigned to the tube.
4. A method according to claim 3, wherein a fourth eccentricity threshold (S4),
higher than the third eccentricity threshold (S3), and a fourth reference length (L4),
correlated to said fourth eccentricity threshold (S4), are defined,
whereby in step b) a fourth sum of lengths of tube portions having eccentricity either higher than or equal to the fourth eccentricity threshold (S4) is also executed,
and in step c) a fifth class is assigned to the tube if the vaiue of said fourth sum is either higher than or equal to said fourth reference length (L4), otherwise a fourth class is assigned to the tube if the vaiue of said third sum is either higher than or equal to said third reference length (L3), otherwise said third class is assigned to the tube if the vaiue of said second sum is either higher than or equal to said second reference length (L2), otherwise said second class is assigned to the tube if the vaiue of said first sum is either higher than or equal to said first reference length (L1), otherwise the first class is assigned to the tube.
5. A method according to claim 4, wherein said first eccentricity threshold (S1) is equal to 2%, said second eccentricity threshold (S2) is equal to 4%, said third eccentricity threshold (S3) is equal to 6%, and said fourth eccentricity threshold (S4) is equal to 8%.
6. A method according to any one of the preceding claims, wherein the eccentricity of the tube along its entire length (Ltot) is detected in a drawing machine (1).
7. A method according to claim 6, wherein the eccentricity is detected by a
detection head (9) arranged downstream of a traction device (10) of the tube of
said drawing machine (1),
8. A method according to claim 6 or 7, wherein said detection head (9) is provided
with transducers (8'), preferably of the ultrasound type and equally angularly
spaced apart from one another.

9. A method according to any one of the preceding claims, wherein there is provided a detection of the length of the tube as a function of time by means of said detection system.