8 Appearance

8.1 Tubes shall have a smooth internal and external sur- face consistent with the cold working process. As a result, the arithmetical mean deviation of the profile, Ra, will be 6,3 цт or less. Lower Ra values shall be subject to agree- ment for quality grade С tubes.

NOTE: For technical reasons, it is not always possible to obtain a smooth surface on tubes with an internal diameter of less than 15 mm.

8.2 Slight surface imperfections such as scabs or gouges, resulting from the manufacturing process, are per- mitted provided the inner and outer diameters, after dress- ing, continue to meet the specified requirements. Scabs, laps or laminations are not permitted.
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).

8.3 As a result of cold working, tubes that have not under- gone heat treatment, i.e. tubes in the BK or BKW condition, are generally covered by a lubricant or grease film on their inner and outer surfaces. An agreement shall be made con- cerning its removal. Tubes that have undergone heat treatment, i.e. tubes in the BKS, GBK or NBK condition, may show signs of scorching, but shall be free of loose scale.

8.4 Where, with regard to subsequent surface treatment (such as galvanizing), special requirements are to be met concerning the surface preparation grade of tubes, such requirements shall be agreed upon at the time of ordering.

8.5 In compliance with commercial practice, the tubes shall be supplied with provisional corrosion protection. If a particular form of corrosion protection (e.g. galvanizing as specified in DIN 50960 Part 1), or none whatsoever, is re- quested, this shall be stated in the order.

9 Dimensions and limit deviations

9.1 Diameter and wall thicknesses

DIN 2391 Part 1 shall apply for the dimensions of seamless precision steel tubes.

If one of the limit deviations for the diameter is to be zero, the limit deviation for the wall thickness shall be equal to 10% of the mean wall thickness calculated using the for-mula given in clause 2 of DIN 2391 Part 1.

9.2 Straightnesss

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 1000 mm apart.
Tubes of 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 straight-ened. As establishing the straightness of such tubes might prove to be difficult, the straightness measuring 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 be-tween 4 m and 7 m.
The number of tubes in lengths from 2 m to below 4 m shall not exceed 15% of the quantity ordered and shall be sup-plied in separate bundles.
Cut lengths shall allow for deviations of + 500 mm of the length ordered, short lengths of 2000mm or more being supplied in separate bundles up to a maximum of 10% of the quantity ordered.

Exact lengths are subject to the following limit deviations:

• for lengths up to 500 mm: +²₀ mm;
• for lengths above 500 mm up to 2000 mm: +³₀ mm;
• for lengths above 2000 mm up to 5000 mm: +⁵₀ mm;
• for lengths above 5000 up to 7000 mm: +¹⁰₀ mm.
• For lengths greater than 7000 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 2391 Parti.
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 7.

Table 7: 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 10233;
• e) a drift expanding test, as specified in DIN EN 10234.

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 50049 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 50049 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 the testing agency if the inspection is carried out by a third party.
Tubes shall be tested at the manufacturer's works. Produc-tion 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 9. 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 10002 Parti.

10.2.2.2 Flattening test

The flattening test shall be carrried out, as specified in DIN EN 10233, 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 30 and St 35, and 0,07 for steel grades St 45 and St 52.
After testing, the samples shall be inspected for cracks.

Table 8: Percentage expansion

10.2.2.3 Drift expanding test

The drift expanding test shall be conducted until the maxi-mum expansion specified in table 8 is reached. It shall be carried out, as described in DIN EN 10 234, on annealed and normalized tubes with a maximum outside diameter of 150 mm and a wall thickness of up to 9 mm.
After testing, the samples shall be inspected for cracks.

10.2.2.4 Measurement of surface roughness

The surface roughness shall be measured axially by using electric stylus instruments as specified in DIN 4768.

10.2.2.5 Dimensional check

The tube dimensions shall be measured with suitable tech-niques.
The type and scope of the dimensional checking of tubes of exact length shall be subject to agreement.

10.2.2.6 Surface inspection

The appearance of the outer and, if possible, inner tube surface shall be examined visually under appropriate light-ing conditions by an inspector having normal vision. If so agreed, another method of checking the appearance may be used. The type and scope of surface inspection of tubes of exact length shall be subject to agreement.

10.2.2.7 Leak tightness test

The tubes shall be tested for leak tightness by using appro-priate non-destructive test methods (e.g. eddy current testing in accordance with Stahl-Eisen-Prufblatt (Iron and steel testing specification) 1925*)).

10.2.2.8 Non-destructive testing

If freedom from imperfections is of particular significance, eddy current testing as specified in PRP 02-74 may be car-ried out, primarily to detect transverse defects. The ultra-sonic test, as specified in Stahl-Eisen-PrQfblatt 1915, is usually conducted to detect longitudinal defects.

10.2.3 Retests

10.2.3.1 Tubes not satisfying the requirements when tested as specified in subclauses 10.2.2.1 to 10.2.2.3 shall be rejected. Two further tubes shall be taken from the batch concerned in place of the rejected sample tube and submit- ted for testing. If one of these two tubes does not fulfill the requirements, the entire batch shall be considered not to comply with the standard.

10.2.3.2 If the defects or deficiencies established can be made good by means of heat treatment or other suitable measures, the supplier shall be given the opportunity to present a batch which was rejected for renewed accept- ance inspection. If the test pieces still fail to satisfy the requirements, the entire batch shall be considered not to comply with the standard.

10.3 Inspection documents

The inspection documents to be issued shall comply with DIN 50049.

Table 9: Scope of testing

11 Quality grade С

Table 10: Special requirements (examples)

12 Marking

A durable tag, containing the following information, shall be securely attached to each bundle:

• a) the manufacturer's mark;
• b) the relevant standard (technical delivery condition) and quality grade;
• c) steel grade, in compliance with table 1;
• d) the final supply condition, in accordance with tale 4;
• e) the dimensions;
• f) the inspector's mark, where tubes are supplied with an inspection document.

Further markings shall be subject to agreement.

13 Bundling

The type of bundling shall be subject to agreement.

14 Complaints

Warranty claims may only be raised if based on the techni-cal delivery conditions specified here or on any further agreement. The purchaser shall give the supplier the opportunity of judging whether the complaint is justified, by submitting the tube objected to and samples of the other tubes supplied.

Standards and documents referred to

DIN 1629 — Seamless, circular, unalloyed steel pipes subject to special requirements; technical delivery conditions

DIN 1630 — High performance seamless, circular, unalloyed steel tubes; technical delivery conditions

DIN 1651 — Free cutting steel; technical delivery conditions

DIN 2391 Part 1 — Seamless precision steel tubes; dimensions

DIN 2445 Part 2 — Seamless precision steel tubes subject to fatigue loading, rated for a pressure of 64 to 400 bar

DIN 4768 — Determination of surface roughness parameters R_a, R_z, and R_max, using electric stylus instruments; concepts and measuring conditions

DIN 8528 Part 1 — Weldability of metallic materials; concepts

DIN 17121 — Seamless circular steel stubes for structural steelwork; technical delivery conditions

DIN 17124 — Seamless circular fine grain steel tubes for structural steelwork; technical delivery conditions

DIN 17172 — Steel pipes for conveying combustible liquids and gases; technical delivery conditions

DIN 17173 — Seamless circular tubes made from steel with low temperature toughness; technical delivery conditions

D|N 17175 — Seamless tubes with elevated temperature properties; technical delivery conditions

D|N 17179 — Seamless circular fine grain steel tubes subject to special requirements; technical delivery conditions

D|N 17204 — Seamless circular tubes made from steels for quenching and tempering; technical delivery conditions

DIN 17210 — Case hardening steel; technical delivery conditions

DIN 17458 — Seamless circular austenitic stainless steel tubes subject to special requirements; technical delivery conditions

DIN 50049 — Inspection documents for the delivery of metallic products

DIN 50 960 Part 1 — Electroplated and chemically applied coatings; designation and information in technical documentation

DIN EN 10 002 Part 1 — Tensile testing of metallic materials; method of test at ambient temperature (including Amendment AC 1:1990)

DIN EN 10025 — Hot rolled unalloyed structural steel products; technical delivery conditions (including Amendment A1:1993)

DIN EN 10027 Part 1 — Designation systems for steel; steel names and principal symbols

DIN EN 10027 Part 2 — Designation systems for steel; numerical system

DIN EN 10083 Part 1 — Quenched and tempered steels; technical delivery conditions for special steels

DIN EN 10083 Part 2 — Quenched and tempered steels; technical delivery conditions for unalloyed quality steels

DIN EN 10233 — Metallic materials; tube; flattening test

DIN EN 10234 — Metallic materials; tube; drift expanding test

Stahl-Eisen-Prufblatt 1915**) — Ultraschallprufung auf Langsfehler von Rohren aus warmfesten Stahlen (Ultrasonic testing for stani bisen ггито,ап >,ongitudini?, imperfections in steel tubes with elevated temperature properties)

Stahl-Eisen-Prufblatt 1925**) — Elektromagnetische Prufung von Rohren zum Nachweis der Dichtheit (Eddy current testing of tubes for leak tightness)

PRP 02-74*) — Prufblatt fur die Wirbelstromprufung von Prazisionsstahlrohren (Specification regarding the

Other relevant standard

DIN EN 10021 — General technical delivery conditions for steel and iron products eddy current testing of seamless precision steel tubes)

Previous editions

DIN 2391 Part 2:1940-06, 1957-11, 1967-07, 1981-07.

*) Obtainable from Fachvereinigung Prazisionsrohrwerke e.V. Postfach 300364, D-40403 Dusseldorf.
**) Obtainable from Vertag Stahlelsen mbH, Postfach 10 51 64, D-40042 Dusseldorf.

Amendments

In comparison with the July 1981 edition, this standard has been revised in form and substance and the following amendments made:

• a) Quality grade В has been dropped and grades A and С redefined.
• b) The outside diameter, the inside diameter and the wall thickness have been referred to as D, D_l and T, respectively, and the order details changed accordingly.
• c) The use of SM steel and unkilled casted steel is no longer specified for precision steel tubes.
• d) Grade С tubes may be made from other steels if these are suitable (cf. table 1).
• e) In table 2 the maximum permissible P and S contents were brought into line with the state of the art and the addition of further alloying elements specified.
• f) A table covering permitted deviations of the product analysis from the specified ladle analysis has been included (cf. table 3).
• g) The BKS 'cold formed and stress-relief annealed' condition has been included and the descriptions provided for the other final supply conditions amended.
• h) Mechanical properties of tubes in the BKS condition have been specified and the minimum values regarding the tensile strength for BK and BKW conditions increased.
• i) The specifications for surface appearance have been completely revised.
• j) With regard to deviations from straightness, a distinction has been made between localized deviations and deviations along the entire tube length.
• k) Random lengths have been limited to a range between 4 m and 7 m.
• I) The requirements for tube ends have been amended.
• m) Specifications regarding divergence between the quantity ordered and the actual consignment now apply to orders for exact lengths only.
• n) Leak tightness tests are no longer specified for quality grade A tubes. If delivery conditions require leak tightness, tubes shall be supplied in quality grade C.
• o) A table covering the scope of testing has been included (cf. table 9).
• p) The requirements regarding the performance of test pipes submitted to flattening and drift expanding tests have been amended.
• q) The procedures regarding surface roughness measurement, dimensional checks and surface inspections, as well as leak tightness tests and non-destructive testing have been altered.

International Patent Classification

F 16 L 009/02

G 01 В 021/30

G 01 N 033/20