8 Appearance

8.1 Tubes shall have a smooth internal and external surface consistent with the sizing process. Except for the weld zone, the arithmetical mean deviation of the profile, R,, will be 6,3 um or less. If particular significance is given to the surface appearance, tubes may be made from cold-rolled steel strip. This shall be subject of agreement at the time of ordering and shall apply for quality grade С tubes.

8.2 The exterior weld flash shall be removed. For tubes with a wall thickness, 7, of up to 1,5 mm, the interior weld flash shall not exceed 0,8 mm in height and not be higher than 0.6 Г for tubes with a wall thickness greater than 1,5 mm. Where, subject to agreement, the interior flash is to be dressed by machining (this being indicated by the symbol IG in the order designation), the residual flash shall not be higher than 0,3 mm and the remaining wall thickness no less than the minimum value specified in this standard.

8.3 Slight surface imperfections such as scabs or gouges, resulting from the manufacturing process, are permitted provided the inner and outer diameters, after dressing, continue to meet the specified requirements. If freedom from imperfections is of particular significance, an appropriate non-destructive test method (such as eddy current or ultrasonic testing) shall be agreed (cf. subclause 10.2.2.8).

8.4 Tubes in the BKM condition that have not undergone heat treatment are generally covered by a lubricant or grease film on their inner and outer surfaces. Agreement shall be reached concerning its removal. Tubes that have undergone heat treatment, i. e. tubes in the GBK or NBK condition, may show signs of scorching, but shall be free of loose scale.

8.5 Whe're, with regard to subsequent surface treatment (such as galvanizing), special requirements are to be met concern- ing the surface preparation grade of tubes, such requirements shall be agreed upon at the time of ordering.

8.6 In compliance with commercial practice, the tubes shall be supplied with provisional corrosion protection. If a particular form of corrosion protection, or none whatsoever, is requested, this shall be stated in the order.

9 Dimensions and limit deviations

9.1 Diameter and wall thicknesses

DIN 2394 Part 1 shall apply for the dimensions of welded and sized precision steel tubes.

9.2 Stralghtness

Tubes with an outside diameter exceeding 15 mm shall not deviate from straightness by more than 0,25 % of the total length. Tubes with a yield strength greater than 500 N/mm2 shall not deviate from straightness by more than 0,3 % of the total length. Localized deviations shall not exceed 3 mm/m and shall be measured as the distance between the tube surface and a chord linking two random points 1 000 mm apart.
Tubesof exact lengths shall not deviate from straightness by more than 0,3 % of the tube length.
In compliance with commercial practice, tubes with an outside diameter of up to 15 mm shall be supplied straightened. As establishing the straightness of such tubes might prove to be difficult, the straightness testing procedure shall be subject to agreement.
More stringent requirements regarding straightness shall be subject to agreement and shall apply for quality grade С tubes.

9.3 Lengths

Unless otherwise specified by the purchaser at the time of ordering, tubes shall be supplied as random lengths between 5 m and 7 m.
The number of tubes in lengths from 2 m to below 5 m hall not exceed 10 % of the quantity ordered and shall be supplied in separate bundles.
Cut lengths shall allow for deviations of +/- 500 mm of the length ordered, short lengths of 2 000 mm or more being supplied in separate bundles up to a maximum of 10 % of the quantity ordered. Exact lengths comply with the following limit deviations:

for lengths up to 500 mm: ⁺²₀ mm;
for lengths above 500 mm up to 2 000 mm: ⁺³₀ mm;
for lengths above 2 000 mm up to 5 000 mm: ⁺⁵₀ mm;
for lengths above 5 000 mm up to 7 000 mm: ⁺¹⁰₀ mm.
For lengths greater than 7 000 mm, limit deviations shall be subject to agreement.

9.4 Tube ends

Tube ends shall be cut nominally square to the tube axis and shall be free from excessive burrs, as may result from the cutting process. Such burrs may cause a change in diameter, exceeding the limit deviations specified in DIN 2394 Part 1.
Agreement regarding the finishing of ends of tubes of exact length is mandatory.

9.5 Divergence between quantity ordered and consignment

Where tubes of exact length have been ordered, deficient supplies shall not be permitted. However, excess supplies shall be permissible in compliance with the specifications given in table 6.

Table 6: Excess supplies

10 Testing

10.1 Tubes to be supplied without inspection document (quality grade A)

As part of internal control, the manufacturer shall submit tubes to:

• a) a dimensional check;
• b) a surface inspection;
• c) a tensile test, as specified in DIN EN 10002 Part 1;
• d) a flattening test, as specified in DIN EN 10 233;
• e) a drift expanding test, as specified in DIN EN 10 234.

Flattening and drift expanding tests shall only be carried out on annealed or normalized tubes made of the steel grades listed in table 2 if testing does not adversely affect the tube diameter and wall thickness. Subject to agreement, a type 2.2 inspection document in compliance with DIN 50 049 shall be issued. Additional tests shall be subject to agreement. They are relevant for quality grade С steels.

10.2 Tubes to be supplied with inspection document (quality grade C)

Should a DIN 50 049 inspection certificate be required for quality grade С steel tubes, this shall be agreed upon at the time of ordering. The order shall state the type of document requested and the name of the testing agency if the inspection is carried out by a third party.
Tubes shall be tested at the manufacturer's works. Production shall not be unduly disturbed if Inspection is carried out by experts who are not employed by the manufacturer.

10.2.1 Scope of testing

Tubes shall be tested by batches. For details, see table 8. For the purpose of testing, tubes shall be divided according to steel grade, final supply condition and size, into batches each comprising 200 units. Remainders of up to 20 units may be distributed uniformly across the other batches, remainders ranging from 20 to 200 units and consignments of less than 200 units being considered a whole batch. 10.2.2 Procedure All tests shall be carried out at ambient temperature.

10.2.2.1 Tensile test

The tensile test shall be carried out as specified in DIN EN 10 002 Part 1.

10.2.2.2 Flattening test

The flattening test shall be carried out, as specified in DIN EN 10 233, on annealed and normalized tubes, the wall thickness of which is less than 15 % of the outside diameter. The test pieces or tube ends shall be flattened until a specified distance between platens, H, is reached. This distance, in mm, is to be calculated on the basis of the following equation:

where Т is the wall thickness, in mm; D is the outside diameter of the tube, in mm; с is a constant, which is 0,09 for steel grades St 34 and St 37, and 0,07 for steel grades St 44 and St 52. After testing, the samples shall be inspected for cracks.

10.2.2.3 Drift expanding test

Annealed and normalized tubes shall be submitted to the drift expanding test as described in DIN EN 10 234 until the maximurr expansion specified in table 7 is reached. After testing, the samples shall be inspected for cracks.

Table 7: Percentage expansion