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
Quantity ordered, in metres
|
Percentage deviation
|
Up to 500
|
+ 20
|
Above 500 up to 2 000
|
+ 15
|
Above 2 000
|
+ 10
|
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
Steel grade
|
Final supply condition
|
Percentage expansion for a wall thickness, in mm,
|
up to 4
|
above 4
|
RSt 34-2
RSt 37-2
St 44-2
St 52-3
|
Normalized or annealed
|
20
18
15
15
|
15
12
10
10
|
|