Seamless precision steel tubes
Technical delivery conditions

ICS 23.040.10

Supersedes July 1981 edition.

Descriptors: Tube, steel tube, precision tube, technical delivery conditions.

Nahtlose Prdzisionsstahlrohre (mit besonderer MaBgenauigkeit); technische Lieferbedingungen

In keeping with current practice in standards published by the International Organization for Standardization (ISO), a comma has been used throughout as the decimal marker.

Dimensions in mm

1 Scope and field of application

1.1 This standard specifies technical delivery conditions for cold finished seamless precision steel tubes of the di- mensions listed in DIN 2391 Part 1, which are made from the steel grades listed in clause 4.
Such tubes are mainly used where accuracy to size and, possibly, a small wall thickness, a particular surface condi-tion and specific mechanical properties are required.

1.2 This standard does not cover:

• seamless circular unalloyed steel tubes subject to special requirements (cf. DIN 1629);
• high performance seamless circular unalloyed steel tubes (cf. DIN 1630);
• seamless circular steel tubes for structural steelwork (cf. DIN 17121);
• seamless circular fine grain steel tubes for structural steelwork (cf. DIN 17124);
• seamless circular tubes made from steel with low- temperature toughness (cf. DIN 17173);
• seamless tubes made from steel with elevated tem- perature properties (cf. DIN 17175);
• seamless circular fine grain steel tubes subject to special requirements (cf. DIN 17179);
• seamless circular tubes made from steel for quench- ing and tempering (cf. DIN 17204);
• seamless circular austenitic stainless steel tubes subject to special requirements (cf. DIN 17458);
• steel pipes for conveying combustible liquids and gases (cf. DIN 17172).

Subject to agreement, tubes of dimensions specified in DIN 2391 Part 1 and in compliance with one of the stand-ards listed above may be ordered in quality grade C.

2 Quality grades

Tubes shall be supplied in the following quality grades:

• for precision steel tubes, that do not require an inspec-tion certificate and thus are not subject to special re-quirements, grade A;
• for precision steel tubes subject to special require-ments, grade C.

In accordance with the stated demands of the purchaser, such special requirements and the relevant test methods shall be the subject of agreement. Table 10 lists possible additional requirements (for grade C).

3 Order details and options

The following information shall be supplied by the pur-chaser:

• a) the quantity, in metres;
• b) a reference to this standard;
• c) the quality grade;
• d) the steel grade;
• e) the final supply condition;
• f) the outside and Inside diameters, or, where relevant, the outside diameter and wall thickness or inside diam- eter and wall thickness;
• g) the type of tube length to be supplied;
• h) any inspection document agreed upon.

Designation for 1000 m seamless precision steel tubes, made of St 35 steel, normalized (NBK) as specified in DIN 2391 Part 1, of quality grade C, with an outside diam-eter, D, of 100 mm and an inside diameter, Dv of 94 mm, in exact lengths of 4000 mm, with type 3.1.В inspection cer-tificate as specified in DIN 50049: 1 000 m tube DIN 2391 -C-St 35 NBK -100x1094x4000-3.1.8

Unless otherwise specified, tubes shall be supplied in qual-ity grade A and in lengths as specified in subclause 9.3.

4 Materials

The tubes shall be manufactured from electric steel or basic oxygen steel, the melting and casting processes being at the discretion of the manufacturer.
The steel shall be cast as killed steel. Table 1 lists relevant steel grades.

5 Chemical composition

5.1 Ladle analysis

The chemical composition of the steels dealt with in this standard shall be as specified in table 2. Small departures from these specifications are permissible if they do not impair the performance of the steel.

5.2 Product analysis

When a product analysis is carried out on finished tubes, the permitted deviations given in table 3 shall apply to the ladle analysis specified in table 2.

Table 1: Steel grades

Table 2: Chemical composition of steel grades shown on ladle analysis

Table 3: Permitted deviations of the product analysis from the specified ladle analysis

6 Final supply conditions

Tubes are to be supplied in one of the conditions specified in table 4.

7 Mechanical properties

7.1 The mechanical properties are a function of the final supply condition (cf. table 4) and shall comply with table 5.

7.2 When tested as described in subclauses 10.2.2.2 and 10.2.2.3, tubes shall show no cracks.

7.3 In the case of steel grades and/or final supply condi- tions other than those specified in tables 2 and 4, the re- quired mechanical properties shall be subject to agree- ment. Such tubes shall be supplied in quality grade C.

7.4 On the basis of their chemical composition and the way they have been processed, the steels listed in table 2 are to be regarded as weldable. It should, however, be noted that the mechanical properties of tubes in the BK, BKW or BKS condition are modified in the zone of the tube which has been subjected to heat (cf. DIN 8528 Part 1).

Table 4: Final supply conditions

Table 5: Mechanical properties of tubes at ambient temperature

¹⁾ The yield strength for the annealed (GBK) condition shall be equal to at least 50% of the tensile strength. Depending on the extent of deformation, the yield strength of tubes supplied in the cold finished (hard) (BK) and cold finished (soft) (BKW) conditions, may come close to reaching the tensile strength. Calculations should be based on a minimum value of 80% of the tensile strength for the cold finished (hard) condition and of 70% for the cold finished (soft) condition.
²⁾ For tubes with an outside diameter of up to 30 mm and a wall thickness up to 3 mm, the minimum yield strength may be 1 0 N/mm² lower.