GB/T 21832.1-2018Welded austenitic-ferritic duplex stainless steel tubes and pipes - Part 1: Tubes for heat exchangers (English PDF)

1 Scope

China's national standard for welded duplex stainless steel tube for heat exchangers. It is Part 1 of GB/T 21832 and specifies the order content, the dimensions, shape and weight, the technical requirements, the test methods, the inspection rules, and the packaging, marking and quality certification. Duplex stainless steel is roughly half austenite and half ferrite, and the mixture gives what neither phase gives alone: about twice the yield strength of an austenitic grade, so a thinner wall carries the same pressure, and far better resistance to chloride stress corrosion cracking, which is the failure that destroys austenitic stainless steel in seawater, in brackish cooling water and in chloride process streams. In a heat exchanger both matter directly. A thinner tube transfers heat better and costs less per metre, and the tube bundle is precisely where chloride cracking occurs, in the crevices at the tubesheet and under deposits. The difficulty is the welding, and that is what most of this standard is about. The phase balance of a duplex steel is set by the composition and by the cooling rate, and a weld cools fast: without control the weld metal and the heat affected zone come out too ferritic, which costs toughness and corrosion resistance, and holding the material in the wrong temperature range precipitates sigma phase, which embrittles it. So the standard specifies the delivery condition and the solution annealing after welding, the corrosion tests, the flattening, flaring and hydrostatic or eddy current tests, and the dimensional tolerances that a tubesheet demands. Issued on 14 May 2018 and in force since 1 February 2019, it replaces GB/T 21832-2008.

This Part of GB/T 21832 specifies the ordering content, dimensions, shape, weight, technical requirements, test methods, inspection rules, packaging, marking and quality certification for welded austenitic-ferritic (duplex) stainless steel tubes for heat exchangers. This Part applies to welded austenitic-ferritic (duplex) stainless steel tubes for heat exchangers (hereinafter referred to as steel tubes).

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition dated applies to this document. For undated references, the latest edition of the referenced documents (including all amendments) applies to this document.

GB/T 222, Permissible tolerances for chemical composition of steel products

GB/T 223.11, Iron, steel and alloy - Determination of chromium content - Visual titration or potentiometric titration method

GB/T 223.18, Methods for chemical analysis of iron, steel and alloy - The sodium thiosulfate separation iodimetric method for the determination of copper content

GB/T 223.19, Methods for Chemical Analysis of Iron Steel and Alloy - the Neocuproine-Chloroform Extraction Photometric Method for the Determination of Copper Content

GB/T 223.25, Methods for chemical analysis of iron, steel and alloy - The dimethylglyoxime gravimetric method for the determination of nickel content

GB/T 223.26, Iron, steel and alloy - Determination of molybdenum content - The thiocyanate spectrophotometric method

GB/T 223.28, Methods for chemical analysis of iron steel and alloy - The alpha- denzoinoxime gravimetric method for the determination of molybdenum content

GB/T 11170, Stainless steel - Determination of multi-element contents - Spark discharge atomic emission spectrometric method (Routine method)

GB/T 13305, Micrographic method for determining area content of the alpha-phases in stainless steels

GB/T 20066, Steel and iron-sampling and preparation of samples for the determination of chemical composition

GB/T 20123, Steel and iron - Determination of total carbon and sulfur content Infrared absorption method after combustion in an induction furnace (routine method)

GB/T 20124, Steel and iron - Determination of nitrogen content - Thermal conductimetric method after fusion in a current of inert gas

GB/T 21835, Dimensions and masses per unit length of welded steel pipes

3 Ordering content

Contracts or orders for purchase of steel tubes based on this Part shall include the following content.

a) a reference to this Part;

b) product name;

c) steel designation;

d) dimensions (outer diameter × wall thickness, in mm);

e) quantity ordered;

f) special requirements.

5 Technical requirements...

7 Inspection rules

7.1 Inspection and acceptance The inspection and acceptance of steel tubes shall be carried out by the quality and technology supervision department of the supplier.

7.2 Group-batch rules Except that chemical composition can be inspected and accepted by furnace, the other test items of steel tubes shall be inspected and accepted by batch. Each batch consist of steel tubes of the same designation, heat number, specification, welding process and heat treatment system (heat). The quantity of each batch of steel tubes shall not exceed those specified as follows:

a) 400 steel tubes for D <= 40 mm;

b) 200 steel tubes for 40 mm < D <= 40 mm;

c) 100 steel tubes for D > 140 mm.

7.3 Sampling quantity The sampling quantity for all tests of each batch of steel tubes shall be as specified in Table 4.

9 Eddy current One by one - GB/T 7735-2016

10 Metallographic structure One sample separately taken from two steel tubes of each batch GB/T 13305 GB/T 13305

11 Corrosion As agreed on As agreed on As agreed on Detrimental intermetallic phase As agreed on As agreed on As agreed on