GB/T 21833.3-2024Seamless austenitic-ferritic (duplex) stainless steel tubes and pipes - Part 3: Pipes for oil and gas transmission (English PDF)

3 Terms and definitions

The terms and definitions given in GB/T 30062 apply to this document.

4 Classification and codes

Pipes are divided into two classes according to the method of manufacture: hot rolled or hot extruded pipe, code W-H; cold drawn or cold rolled pipe, code W-C.

5 Information for ordering

The contract or order for pipe purchased to this document shall include, but is not limited to, the number of this document; the name of the product; the grade of the steel or its unified numerical code; the dimensions, that is the nominal outside diameter multiplied by the nominal wall thickness, in millimetres; the quantity ordered, as total mass or total length; the delivery condition; the optional requirements; and any special requirements.

6 Dimensions, shape, mass and permissible deviations

6.1 Outside diameter and wall thickness. The nominal outside diameter and the nominal wall thickness of the pipe shall meet the requirements of GB/T 17395. Pipe of other outside diameters and wall thicknesses may be supplied at the request of the purchaser and by agreement between purchaser and supplier. The permissible deviations of the nominal outside diameter and the nominal wall thickness shall meet the requirements of Table 1, which sets an ordinary grade and a high grade of tolerance for each of the two classes of manufacture, expressed for the outside diameter partly as a fixed value in millimetres and partly as a percentage of the diameter, and for the wall thickness as a percentage of the wall thickness; the individual values of Table 1 are not reproduced here because the columns of the table could not be paired with certainty in the source. Where the contract does not state the grade of dimensional tolerance, the permissible deviations of outside diameter and wall thickness are those of the ordinary grade.

6.2 Length. The usual length of the pipe is 6000 mm to 12000 mm. Pipe in another range of length may be supplied at the request of the purchaser, by agreement and with a note in the contract. Exact lengths, multiple lengths or other specified lengths may likewise be supplied; the total length of exact and multiple lengths shall lie within the usual range and the permissible deviation on the whole length is plus 100 mm. For pipe delivered in multiple lengths an allowance of 5 mm to 10 mm shall be left at each cut.

6.3 Straightness. The deviation from straightness of the pipe shall not exceed 1.5 mm per metre, and over the whole length shall not exceed 0.2 % of the length of the pipe.

6.4 Out-of-roundness and wall thickness variation. The out-of-roundness and the wall thickness variation of the pipe shall not exceed 80 % of the tolerance on outside diameter and of the tolerance on wall thickness respectively.

6.5 Shape of the ends. Both ends of the pipe shall be cut square to the axis of the pipe and the burrs shall be removed. At the request of the purchaser, by agreement and with a note in the contract, the two ends may be bevelled; the root face width is (1.6 +/- 0.8) mm, while the bevel angle and its tolerance came out damaged in the source and are not reproduced here. Other forms of bevel may be specified in the contract.

6.6 Mass. The pipe is delivered by actual mass, or by theoretical mass. The theoretical mass per metre is calculated by Formula (1) from the nominal wall thickness and the nominal outside diameter in millimetres, with the ratio of the circumference to the diameter taken as 3.1416 and the density of the steel taken as 7.80 kg per cubic decimetre; the theoretical mass is expressed in kilograms per metre.

7 Technical requirements

7.1 Grade and chemical composition of the steel. The grade and the chemical composition on cast analysis shall meet the requirements of Table 2, which covers nine grades with their unified numerical codes: S22253 022Cr22Ni5Mo3N, S22053 022Cr23Ni5Mo3N, S25203 022Cr25Ni7Mo4CuN, S22553 022Cr25Ni6Mo2N, S22583 022Cr25Ni7Mo3WCuN, S22584 022Cr25Ni7Mo3W2CuN, S25073 022Cr25Ni7Mo4N, S27603 022Cr25Ni7Mo4WCuN and S25554 03Cr25Ni6Mo3Cu2N. For each grade the table fixes limits on carbon, silicon, manganese, phosphorus, sulfur, nickel, chromium, molybdenum, nitrogen and copper, and for three grades a tungsten content. The footnotes fix the pitting resistance equivalent number as chromium plus 3.3 times molybdenum plus 16 times nitrogen, which shall be not less than 34 for 022Cr22Ni5Mo3N, not less than 35 for 022Cr23Ni5Mo3N and not less than 41 for 022Cr25Ni7Mo4N; for 022Cr25Ni7Mo4WCuN the equivalent is chromium plus 3.3 times the sum of molybdenum and one half of the tungsten, plus 16 times nitrogen, and shall be not less than 41. Where the purchaser has requirements for other chemical elements, these may be agreed with the supplier and noted in the contract. The permissible deviations of the chemical composition of the finished pipe shall meet the requirements of GB/T 222.

7.2 Manufacturing method. The steel shall be melted in an electric arc furnace with secondary refining, or in a converter with secondary refining; other melting methods may be used by agreement between purchaser and supplier with a note in the contract. The pipe shall be made by the seamless process, hot rolled or hot extruded, or cold drawn or cold rolled.

7.3 Delivery condition. The pipe shall be delivered heat treated and pickled. Pipe heat treated under a protective atmosphere, or ground or polished all over, may be delivered without pickling. The recommended heat treatment for the pipe is given in Table 3, and heat treatments other than those of Table 3 may be used by agreement with a note in the contract. Table 3 gives, for each grade, the recommended heat treatment and, as minimum values, the tensile strength, the proof strength at 0.2 % non-proportional extension and the elongation after fracture, and, as maximum values, the Brinell and Rockwell C hardness: S22253 022Cr22Ni5Mo3N, 1020 °C to 1100 °C and rapid cooling, 620 MPa, 450 MPa, 25 %, 290 HBW, 30 HRC; S22053 022Cr23Ni5Mo3N, 1020 °C to 1100 °C and rapid cooling, 655 MPa, 485 MPa, 25 %, 290 HBW, 30 HRC; S25203 022Cr25Ni7Mo4CuN, 1080 °C to 1120 °C and rapid cooling, 770 MPa, 550 MPa, 25 %, 310 HBW, 32 HRC; S22553 022Cr25Ni6Mo2N, 1050 °C to 1100 °C and rapid cooling, 690 MPa, 450 MPa, 25 %, 280 HBW, 29 HRC; S22583 022Cr25Ni7Mo3WCuN, 1020 °C to 1100 °C and rapid cooling, 690 MPa, 450 MPa, 25 %, 290 HBW, 30 HRC; S22584 022Cr25Ni7Mo3W2CuN, 1025 °C to 1125 °C and rapid cooling, 758 MPa, 552 MPa, 20 %, 310 HBW, 32 HRC; S25073 022Cr25Ni7Mo4N, 1025 °C to 1125 °C and rapid cooling, 800 MPa, 550 MPa, 15 %, 300 HBW, 32 HRC; S27603 022Cr25Ni7Mo4WCuN, 1070 °C to 1140 °C and rapid cooling, 750 MPa, 550 MPa, 25 %, 300 HBW, 32 HRC; S25554 03Cr25Ni6Mo3Cu2N, not below 1040 °C and rapid cooling, 760 MPa, 550 MPa, 15 %, 297 HBW, 31 HRC.

7.4 Mechanical properties. The longitudinal tensile properties at room temperature of pipe delivered in the heat treated condition shall meet the requirements of Table 3. Where the size of the pipe allows a transverse tensile specimen to be taken, the transverse tensile test may replace the longitudinal test and the results shall meet the requirements of Table 3. Pipe with a wall thickness of not less than 1.7 mm shall be subjected to a Brinell or Rockwell hardness test and the value shall meet the requirements of Table 3. At the request of the purchaser, by agreement and with a note in the contract, the pipe may be impact tested, the test temperature and the absorbed energy being agreed between purchaser and supplier. Where sub-size impact specimens are used, the required minimum Charpy V-notch absorbed energy is the value required for the full-size specimen multiplied by the reduction factor of Table 4, which is 1 for the standard specimen of 10 mm x 10 mm, 0.75 for the small specimen of 10 mm x 7.5 mm and 0.5 for the small specimen of 10 mm x 5 mm.

7.5 Hydrostatic test. Every pipe shall be hydrostatically tested. The test pressure is calculated by Formula (2) and the maximum test pressure is 20 MPa. Under the test pressure the pressure shall be held for not less than 10 s and the pipe shall show no leakage. The content of chloride ions in the water used for the hydrostatic test shall not exceed 0.005 % by mass. In the formula the test pressure is expressed in megapascals and is rounded to the nearest 0.5 MPa when it is below 7 MPa and to the nearest 1 MPa when it is 7 MPa or above; the nominal wall thickness and the nominal outside diameter are expressed in millimetres, and the allowable stress is 75 % of the minimum proof strength at 0.2 % non-proportional extension specified in Table 3, expressed in megapascals.

7.6 Technological properties. Flattening: pipe with a wall thickness not greater than 10 mm shall be subjected to the flattening test. The specimen shall be flattened until the distance between the two platens reaches the value calculated by Formula (3) from the nominal wall thickness and the nominal outside diameter in millimetres, with a deformation coefficient per unit length of 0.07; after the test the specimen shall show no crack or split. Flaring: at the request of the purchaser, by agreement and with a note in the contract, pipe with a nominal outside diameter not greater than 150 mm and a wall thickness not greater than 10 mm may be subjected to the flaring test; the taper of the mandrel is 60° and the minimum flare ratio of the outside diameter of the specimen after flaring is 10 %; after the test the specimen shall show no crack or split.

7.7 Metallographic structure. The structure of the pipe shall be austenite and ferrite, and the ferrite content shall be 40 % to 60 %.

7.8 Test for detrimental precipitated phases. At the request of the purchaser, by agreement and with a note in the contract, the pipe may be tested for detrimental precipitated phases; the test method and the requirements shall meet Annex A.

7.9 Non-destructive testing. Every pipe shall be examined by ultrasonic testing; the artificial flaw in the reference tube shall meet GB/T 5777 and the acceptance level is U3. At the request of the purchaser, by agreement and with a note in the contract, the pipe may be examined by eddy current testing; the artificial flaw in the reference tube shall meet GB/T 7735 and the acceptance level is E3H or E3.

7.10 Surface quality. The inner and outer surfaces of the pipe shall be smooth and free from cracks, laps, rolled-in slivers, laminations and scabs. Such defects shall be completely removed; the depth of removal shall not exceed the lower deviation of the nominal wall thickness and the actual wall thickness at the dressed place shall not be less than the minimum permitted wall thickness. Other local defects not exceeding the lower deviation of the wall thickness are allowed to remain.

7.11 Special requirements. At the request of the purchaser, by agreement and with a note in the contract, the following may be added: adjustment of the ranges of chemical composition given in Table 2; a ferrite content different from that required in 7.7; a pitting corrosion test; a stress corrosion test; and other requirements.

8 Test methods

8.1 Sampling for the chemical analysis of the pipe follows GB/T 20066. The chemical analysis is normally carried out in accordance with GB/T 11170, GB/T 20123, GB/T 20124, YB/T 4395, YB/T 4396 or other common methods; in case of arbitration the methods of the GB/T 223 series listed in Clause 2 and of YB/T 4395 and YB/T 4396 shall be followed.

8.2 The dimensions and the shape of the pipe shall be measured pipe by pipe with measuring instruments of adequate accuracy.

8.3 The inner and outer surfaces of the pipe shall be inspected visually pipe by pipe under adequate illumination.

8.4 The sampling and the test methods for the other inspection items shall meet Table 5. That table sets, for each item, the number of specimens, the method of sampling and the method of test: one specimen per heat for the cast analysis and one per heat for the product analysis; one specimen from each of two pipes per lot for the tensile, hardness, flattening, flaring and metallographic tests; one set of three specimens per lot for the impact test; pipe by pipe for the hydrostatic test, the ultrasonic test and the eddy current test; and by agreement for the test for detrimental precipitated phases, the pitting corrosion test and the stress corrosion test.

9 Inspection rules

9.1 The inspection and acceptance of the pipe shall be carried out by the quality and technical supervision department of the supplier.

9.2 The pipe is inspected and accepted by lots. If the pipe is not heat treated again after being cut into single lengths, all the lengths cut from one heat treated pipe shall be regarded as one pipe. Each lot shall consist of pipe of the same grade, the same heat number, the same size and the same heat treatment charge, and the number of pipes in a lot shall not exceed 500 for pipe with an outside diameter not greater than 76 mm and a wall thickness not greater than 3 mm, 50 for pipe with an outside diameter greater than 351 mm, and 200 for other sizes.

9.3 The number of specimens taken from each lot for each inspection item shall meet Table 5.

9.4 The retest and the rules for judgement shall meet GB/T 2102.

10 Packaging, marking and quality certificate

The packaging, the marking and the quality certificate of the pipe shall meet the requirements of GB/T 2102.

A Annex A (normative) Test methods for detrimental precipitated phases and evaluation of the results

A.1 General. The annex specifies two sets of test conditions and methods for the detection of detrimental precipitated phases in austenitic-ferritic duplex stainless steel: test method A, the sodium hydroxide etch test, used to detect the presence of detrimental precipitated phases; and test method B, the ferric chloride corrosion test, used to detect their presence and their effect on corrosion resistance. Both methods apply to the detection of detrimental phases precipitated during production and manufacture, for example during heat treatment, or during long service at a given temperature; they do not apply to a loss of corrosion resistance arising from other causes. Method A may be used as a rapid screening test before method B. The grades to which the methods apply are 022Cr22Ni5Mo3N (S22253), 022Cr23Ni5Mo3N (S22053), 022Cr25Ni7Mo4CuN (S25203), 022Cr25Ni7Mo4N (S25073), 022Cr25Ni7Mo4WCuN (S27603) and 03Cr25Ni6Mo3Cu2N (S25554).

A.2.1 Test method A, sodium hydroxide etch test. The apparatus comprises a direct current supply of about 15 V and 20 A, such as a battery, generator or rectifier; an ammeter with a measuring range of 0 A to 30 A; a variable resistor, an ammeter and a variable resistor being placed in the circuit to measure and control the current during etching; electrodes, the metal to be etched forming the positive electrode and a piece of metal of the same size and shape as the specimen the negative electrode; a clamp to hold the specimen; a metallographic microscope with a maximum magnification of not less than 500 times; an electrolytic cell for etching; and the electrolyte, reagent grade sodium hydroxide.

A.2.1.2 Procedure of method A. A longitudinal or a transverse section is chosen for the test; unless otherwise specified the size of the specimen is settled by the supplier. After the specimen has been cut, any high temperature or deformation associated with the cutting that would affect the material shall be removed by grinding or machining before the test. The specimen shall allow the section to be examined over the whole thickness; where the section is large, it shall allow examination from one surface to half the thickness, that half thickness included. The surface of the cross-section shall be polished, and the polished surface shall be fit for examination at 500 times. The etching solution may be prepared by adding 40 g of reagent grade sodium hydroxide to 100 g of distilled water. The polished specimen shall be etched for 5 s to 60 s at a direct voltage of 1 V to 3 V. When platinum is used as the negative electrode and etching is carried out for 5 s to 60 s at 1 V to 3 V, any detrimental intermetallic phase appears yellow while the ferrite darkens and then turns brown. After etching the specimen shall be washed thoroughly with hot water, acetone or alcohol and dried in air.

A.2.1.3 Etched structures. The whole etched surface shall be examined under the metallographic microscope at 500 times. The etched structures fall into the following classes. Unaffected structure, Figure A.1: the ferrite has been etched, there is no detrimental intermetallic phase and the boundaries between the phases are smooth. Possibly affected structure, Figure A.2: the ferrite has been etched and free structures that may be detrimental intermetallic phases are shown, the boundaries between the phases possibly showing a fine wavy outline. Affected structure, Figure A.3: during etching the detrimental intermetallic phase appears quickly, before or at the same time as the darkening of the ferrite. Centre line structure, Figure A.4: a continuous or discontinuous intermetallic phase is observed in the region at half the thickness of the product, and outside that region an affected structure showing composition segregation may or may not be present.

A.2.1.4 Evaluation of the results of method A, Table A.1. The unaffected structure of Figure A.1 and the possibly affected structure of Figure A.2 are acceptable etched structures; the affected structure of Figure A.3 and the centre line structure of Figure A.4 are unacceptable.

A.2.2 Test method B, ferric chloride corrosion test. Before the ferric chloride corrosion test a rapid screening may be made with the sodium hydroxide etch test of method A: specimens showing an unaffected structure in method A need not undergo the ferric chloride corrosion test, and all other specimens shall undergo it. The apparatus comprises a 1000 mL glass beaker, a 1000 mL tall or conical flask, a wide-necked tube or a tube of 50 mm diameter or another suitable vessel; a glass support of suitable shape that keeps the specimen in the middle of the test solution; and a water bath or oil bath held at constant temperature.

A.2.2.3 Test solution. The test solution is prepared by dissolving 100 g of reagent grade ferric chloride hexahydrate in 900 mL of distilled water, the ferric chloride amounting to about 6 % by mass. The solution is filtered through glass wool or filter paper to remove insoluble particles. Before the test is started the pH of the solution is adjusted to about 1.3 with hydrochloric acid or sodium hydroxide as required.

A.2.2.4 Specimens. The dimensions of the specimen are measured with a vernier caliper and the total area and the effective test area are calculated; the total surface area of the specimen shall be more than 10 square centimetres. A specimen convenient for testing is cut, its surface containing the full thickness of the product or, for very thick products, at least half the thickness. After the specimen has been cut, any high temperature or deformation associated with the cutting that would affect the material shall be removed by grinding or machining before the test. Scale adhering to the specimen shall be removed by cutting or grinding. Where a uniform surface roughness is required, a grinding machine may be used. The surface of the specimen shall not be passivated with nitric, citric or phosphoric acid, nor pickled with hydrofluoric acid or the like. The prepared specimen shall be cleaned with magnesium oxide paste or a similar material, rinsed with water, immersed in alcohol or acetone and dried in air; it is then weighed to 0.1 mg or better and kept in a dry container until use.

A.2.2.5 Procedure of method B. The volume of ferric chloride solution used shall be at least 20 mL per square centimetre of specimen surface. The test temperature and the acceptance criterion are given in Table A.2: 25 °C +/- 1 °C for S22253 022Cr22Ni5Mo3N and for S22053 022Cr23Ni5Mo3N, and 40 °C +/- 1 °C for S25203, S25073 022Cr25Ni7Mo4N, S27603 022Cr25Ni7Mo4WCuN and S25554 03Cr25Ni6Mo3Cu2N, the corrosion rate in every case being not greater than 10 mg per square decimetre per day. The test period is 24 h. At the end of the 24 h period the specimen is taken out of the solution, rinsed with water, brushed under running tap water with a soft bristle brush to remove the corrosion products, immersed in acetone or alcohol and dried in air. The specimen is then weighed to 0.1 mg or better and kept until any retest.

A.2.2.6 Evaluation of the results of method B. The corrosion rate is expressed as the loss in mass per unit area and per unit time and is calculated by Formula (A.1) from the mass of the specimen before and after the test in milligrams, the total area of the specimen in square decimetres and the duration of the test in days. Unless otherwise stated the calculated corrosion rate shall not exceed 10 mg per square decimetre per day. If the specimen shows a corrosion rate above that value, two new specimens may be taken from the same product and tested again, and the results shall meet the requirement. A product that fails the ferric chloride corrosion test may be given one solution treatment and then sampled and tested again.