GB/T 21832.3-2024Welded austenitic-ferritic (duplex) stainless steel tubes and pipes - Part 3: Pipes for oil and gas transmission (English PDF)

4 Classification and codes

Pipes are classified by delivery condition with the following codes: as-welded condition, H; heat-treated condition, T.

5 Ordering information

The contract or order for pipes to this document shall include, but is not limited to: the number of this document; the product name; the steel designation or unified numerical code; the size (nominal outside diameter times nominal wall thickness, in millimetres); the quantity ordered, as total mass or total length; the delivery condition; and any special requirements.

6 Dimensions, shape, mass and permissible deviations

6.1 The nominal outside diameter and nominal wall thickness shall comply with GB/T 21835; other diameters and wall thicknesses may be supplied by agreement between supplier and purchaser. Permissible deviations of outside diameter and wall thickness shall comply with Table 1, and by agreement, stated in the contract, pipes with deviations other than those of Table 1 may be supplied. For pipes with an outside diameter greater than 508 mm, the difference between the outside diameter converted from a circumference measurement and the nominal outside diameter shall comply with Table 1. Table 1 gives the outside diameter deviation as plus 0.4 mm and minus 0.8 mm for a nominal outside diameter not greater than 48.3 mm, +/- 0.75 % of the nominal outside diameter for diameters above 48.3 mm and up to 457 mm, and +/- 1 % of the nominal outside diameter for diameters above 457 mm; a footnote states that the weld area is not subject to the upper limit of the wall thickness deviation. The extractor did not preserve the row boundaries of the wall thickness column, so the wall thickness deviations are not reproduced here.

6.1.4 By agreement between supplier and purchaser, stated in the contract, the pipe ends may be checked with a ring gauge, in accordance with Table 2. Within 100 mm of the pipe end, a ring gauge with an inside diameter of the nominal outside diameter plus 1.6 mm shall pass over the end for pipes with a nominal outside diameter not greater than 273.1 mm, and a ring gauge with an inside diameter of the nominal outside diameter plus 2.4 mm shall pass over the end for the intermediate diameter range up to 508 mm; for diameters greater than 508 mm, the requirement of 6.1.3 applies. Where the pipe has weld reinforcement, a notch or groove may be cut in the ring gauge so that it can pass over the weld.

6.2 The usual length of the pipes is 6 000 mm to 12 000 mm; other length ranges may be supplied by agreement, stated in the contract. Exact lengths, multiple lengths or other length requirements may also be supplied by agreement. Exact and multiple total lengths shall lie within the usual length range and the permissible deviation on the total length is plus 100 mm. For pipes delivered in multiple lengths, an allowance of 5 mm to 10 mm shall be left for each cut.

6.3 The straightness deviation shall be not more than 1.5 mm per metre and not more than 0.2 % of the pipe length over the full length.

6.4 For thin-walled pipes whose ratio of wall thickness to outside diameter is not greater than 3 %, the out-of-roundness shall not exceed 1.5 % of the nominal outside diameter; for other pipes the out-of-roundness shall not exceed the outside diameter tolerance.

6.5 Both ends of the pipe shall be cut square to the pipe axis and burrs shall be removed. By agreement, stated in the contract, the ends may be bevelled, with a root face width of 1.6 mm plus or minus 0.8 mm; the bevel angle is given in the original as a nominal 30 degrees with a one-sided tolerance, but the extracted text does not allow the tolerance to be read with certainty. Other types of bevel may be specified in the contract.

6.6 Pipes are delivered on the basis of theoretical mass; by agreement, stated in the contract, they may be delivered on the basis of actual mass. The theoretical mass per metre is calculated by Formula (1), in which the mass per metre is expressed in kilograms per metre, the constant pi is taken as 3.1416, the density of the steel is taken as 7.80 kilograms per cubic decimetre, and the nominal wall thickness and nominal outside diameter are expressed in millimetres. When delivered on the basis of theoretical mass, the permissible deviation of the actual mass from the theoretical mass is plus 10 % and minus 3.5 %.

7 Technical requirements

7.1 The steel designation and chemical composition on cast analysis shall comply with Table 3. Table 3 fixes, for each unified numerical code and steel designation covered by the document, the limits on the individual alloying and residual elements of the cast analysis, together with the corresponding equivalent designations. The extracted text of Table 3 is corrupted and none of its values can be read, so no composition limits are reproduced here. The permissible deviations of the chemical composition of the finished pipe shall comply with GB/T 222.

7.2 The steel shall be melted in an electric arc furnace or converter with secondary refining; other melting methods may be used by agreement, stated in the contract. Pipes may be made by any one of the following methods: submerged arc welding with filler metal; gas metal arc welding with filler metal; plasma arc welding with or without filler metal; gas tungsten arc welding with or without filler metal; or combined welding with or without filler metal. Where the purchaser specifies one welding method, this shall be stated in the contract. Where a filler metal is used, it shall match the specified chemical composition of the parent metal; where the purchaser requires higher corrosion resistance or other properties, a more highly alloyed filler metal may be specified. By agreement, stated in the contract, pipes with an outside diameter not less than 508 mm may have two longitudinal welds, the circumferential distance between them being not less than 300 mm.

7.3 Pipes shall be delivered heat treated, pickled and passivated. By agreement, stated in the contract, they may be delivered in the as-welded condition, in which case the mark H shall be applied to the pipe. The recommended heat treatment practice is given in Table 4. Pipes that have been ground or bored all over need not be pickled before delivery.

7.3 Table 4 gives, for eight steels, the recommended heat treatment and the mechanical properties. For S22253 (022Cr22Ni5Mo3N): rapid cooling from 1 020 °C to 1 100 °C; tensile strength not less than 620 MPa; proof strength at 0.2 % plastic extension not less than 450 MPa; elongation after fracture not less than 25 %; hardness not more than 290 HBW or 30 HRC. For S22053 (022Cr23Ni5Mo3N): rapid cooling from 1 020 °C to 1 100 °C; 655 MPa; 485 MPa; 25 %; 290 HBW or 30 HRC. For S22553 (022Cr25Ni6Mo2N): rapid cooling from 1 050 °C to 1 100 °C; 690 MPa; 450 MPa; 25 %; 280 HBW or 29 HRC. For S22583 (022Cr25Ni7Mo3WCuN): rapid cooling from 1 020 °C to 1 100 °C; 690 MPa; 450 MPa; 25 %; 290 HBW or 30 HRC. For S22584 (022Cr25Ni7Mo3W2CuN): rapid cooling from 1 025 °C to 1 125 °C; 758 MPa; 552 MPa; 20 %; 310 HBW or 32 HRC. For S25073 (022Cr25Ni7Mo4N): rapid cooling from 1 025 °C to 1 125 °C; 800 MPa; 550 MPa; 15 %; 300 HBW or 32 HRC. For S27603 (022Cr25Ni7Mo4WCuN): rapid cooling from 1 100 °C to 1 140 °C; 750 MPa; 550 MPa; 25 %; 300 HBW or 32 HRC. For S25554 (03Cr25Ni6Mo3Cu2N): rapid cooling from not less than 1 040 °C; 760 MPa; 550 MPa; 15 %; 297 HBW or 31 HRC.

7.4 Pipes shall be subjected to a tensile test on the parent metal, the longitudinal tensile properties at room temperature complying with Table 4. A transverse parent metal tensile test may replace the longitudinal test, the transverse properties complying with Table 4, but in case of dispute the longitudinal properties govern. Pipes with an outside diameter not less than 219.1 mm shall be subjected to a transverse weld tensile test; the specimen is taken transversely from the pipe or from a welded test plate of the same designation, cast, welding procedure and heat treatment, with the weld at the centre of the specimen and perpendicular to its axis, and the transverse weld tensile strength shall comply with Table 4. Pipes shall be subjected to a Rockwell or Brinell hardness test on the parent metal, the values complying with Table 4; by agreement, stated in the contract, a weld hardness test or a Vickers hardness test may also be carried out, the values being agreed between the parties. By agreement, stated in the contract, a weld impact test may be carried out, the test temperature and absorbed energy being agreed; where subsize specimens are used, the minimum required Charpy V-notch absorbed energy is the full-size requirement multiplied by the reduction factor of Table 5, which is 1 for the standard 10 mm by 10 mm specimen, 0.75 for the 10 mm by 7.5 mm subsize specimen and 0.5 for the 10 mm by 5 mm subsize specimen.

7.5 Pipes with an outside diameter not greater than 219.1 mm shall be subjected to a flattening test, with the weld placed at 90 degrees to the direction of the applied force; the specimen is flattened until the distance between the two platens equals the value calculated by Formula (2), in which the platen distance and the nominal wall thickness and nominal outside diameter are in millimetres and the deformation coefficient per unit length is taken as 0.07. After the test the specimen shall show no crack or fissure. Pipes with an outside diameter greater than 219.1 mm shall be subjected to a weld bend test, the specimen being taken from the pipe or from a welded test plate of the same designation, cast, welding procedure and heat treatment. One set of bend tests comprises one face bend and one root bend, that is, with the outside weld and the inside weld in turn on the maximum bend surface; for pipes with a wall thickness greater than 10 mm, a set of two side bends may replace the face and root bends. The bend former diameter is four times the specimen thickness and the bend angle is 180 degrees; after bending, the weld area shall show no crack or fissure.

7.6 Every pipe shall be subjected to a hydrostatic test. The test pressure is calculated by Formula (3), the maximum test pressure being 20 MPa. In Formula (3) the test pressure is in MPa and is rounded to the nearest 0.5 MPa below 7 MPa and to the nearest 1 MPa at 7 MPa and above; the permissible stress is 75 % of the minimum proof strength at 0.2 % plastic extension specified in Table 4, in MPa; and the nominal wall thickness and nominal outside diameter are in millimetres. The test pressure shall be held for not less than 10 s and the pipe shall show no leakage. The chloride ion content of the water used for the hydrostatic test shall be not more than 0.005 % by mass.

7.7 Pipes shall be subjected to metallographic examination. The structure shall be austenite plus ferrite and the ferrite content of the parent metal area shall be 40 % to 60 %. By agreement between supplier and purchaser, the ferrite content of the weld area, including the heat-affected zone, may be specified.

7.8 The full length of the weld shall be subjected to 100 % radiographic testing, assessed in accordance with GB/T 40791 or GB/T 40385, the testing technique level complying with level A. For pipes with an outside diameter less than 219.1 mm, eddy current or ultrasonic testing may replace radiographic testing; for eddy current testing the artificial flaw in the reference pipe shall comply with acceptance level E3H or E3 of GB/T 7735, and for ultrasonic testing with acceptance level U3 of GB/T 5777. By agreement, stated in the contract, the bevelled end faces may be subjected to penetrant testing in accordance with GB/T 42677.

7.9 The inside and outside surfaces shall be smooth and free from cracks, lack of penetration, weld undercut on the inside, laps and laminations. Such defects shall be removed completely, the depth of removal not exceeding the lower deviation of the nominal wall thickness and the actual wall thickness at the dressed area being not less than the minimum permissible wall thickness. Other local imperfections that do not take the wall below the minimum permissible thickness are allowed. Weld defects may be repaired; the same position may be repair welded not more than three times and the total length of repair weld shall not exceed 20 % of the total weld length. Pipes delivered in the heat-treated condition shall be heat treated after repair welding. After repair welding the weld shall be subjected to the hydrostatic test, to local non-destructive testing and to the surface quality check in accordance with 7.6, 7.8 and 7.9. The outside weld reinforcement shall not exceed 2 mm. The inside weld reinforcement shall not exceed 10 % of the wall thickness for pipes with a nominal outside diameter below 139.7 mm; 15 % of the wall thickness and not more than 2 mm for diameters from 139.7 mm to 323.9 mm; and 20 % of the wall thickness and not more than 3 mm for diameters above 323.9 mm.

7.10 By agreement, stated in the contract, first-article inspection may be carried out. It may further include one or more of the following tests on the parent metal or the weld: pitting corrosion test; stress corrosion test; detrimental precipitated phase test. The result of a first-article inspection is valid for pipes of the same manufacturing method, delivery condition and steel designation.

7.11 By agreement, stated in the contract, the following special requirements may be added: adjustment of the chemical composition ranges of Table 3; a ferrite content different from that required by 7.7; other requirements.

8 Test methods

8.1 Sampling for chemical analysis follows GB/T 20066. Chemical analysis normally follows GB/T 11170, GB/T 20123, GB/T 20124, YB/T 4395, YB/T 4396 or other common methods; in case of dispute the analysis follows the relevant parts of the GB/T 223 series listed in the document together with YB/T 4395 and YB/T 4396.

8.2 The dimensions, shape and weld reinforcement shall be measured on every pipe; for pipes with a nominal outside diameter greater than 508 mm a diameter tape may be used to measure the outside diameter.

8.3 The inside and outside surface quality shall be inspected visually on every pipe under adequate lighting.

8.4 The sampling and test methods for the other inspection items shall comply with Table 6. Table 6 requires: one sample per cast for the cast analysis and one sample per cast for the product analysis, sampled to GB/T 20066 and analysed as in 8.1; one sample per batch for the tensile test, sampled to GB/T 2975 and tested to GB/T 228.1; one sample per batch for the weld tensile test, sampled and tested to GB/T 2651; one sample per batch for hardness, sampled and tested to GB/T 230.1, GB/T 231.1 and GB/T 4340.1; one set of three samples per batch for the weld impact test, sampled and tested to GB/T 2650; one sample per batch for flattening, sampled and tested to GB/T 246; one set of two samples per batch for the weld bend test, sampled and tested to GB/T 2653; the hydrostatic test on every pipe to GB/T 241; one sample per batch for the metallographic structure, sampled and tested to GB/T 13305; radiographic testing on every pipe to GB/T 40791 and GB/T 40385; eddy current testing on every pipe to GB/T 7735; ultrasonic testing on every pipe to GB/T 5777; liquid penetrant testing on every pipe to GB/T 42677; the pitting corrosion test by agreement, sampled and tested to GB/T 17897; the stress corrosion test by agreement, sampled by agreement and tested to GB/T 15970 (all parts); and the detrimental precipitated phase test by agreement, sampled by agreement and tested in accordance with Annex A.

9 Inspection rules

9.1 Inspection and acceptance of the pipes shall be carried out by the quality and technical supervision department of the supplier.

9.2 Pipes shall be inspected and accepted in batches. Each batch shall consist of pipes of the same designation, cast, size, welding procedure and heat treatment practice or furnace charge, and the number of pipes in a batch shall not exceed: 400 pipes for an outside diameter not greater than 60.3 mm; 200 pipes for an outside diameter greater than 60.3 mm but not greater than 219.1 mm; 100 pipes for an outside diameter greater than 219.1 mm.

9.3 The number of samples for each inspection item in a batch shall comply with Table 6.

9.4 Retesting and the decision rules shall comply with GB/T 2102.

10 Packaging, marking and quality certificate

The packaging, marking and quality certificate of the pipes shall comply with GB/T 2102.

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

A.1 The annex specifies two sets of test conditions and detection methods for detrimental precipitated phases in austenitic-ferritic duplex stainless steel and its welds: test method A, a sodium hydroxide etch test, used to detect the presence of detrimental precipitated phases; and test method B, a 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 and welding, or during long-term service at a given temperature, and do not apply to a loss of corrosion resistance arising from other causes. Method A may be used as a rapid screen before method B. The steel designations covered are 022Cr22Ni5Mo3N (S22253), 022Cr23Ni5Mo3N (S22053), 022Cr25Ni7Mo4N (S25073), 022Cr25Ni7Mo4WCuN (S27603) and 03Cr25Ni6Mo3Cu2N (S25554).

A.2.1 The apparatus for the sodium hydroxide etch test comprises: a direct current source 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 metallurgical microscope with a maximum magnification of not less than 500 times; an electrolytic cell for etching; and reagent-grade sodium hydroxide as the electrolyte.

A.2.1.2 A longitudinal or transverse section is selected for the test. Unless otherwise specified, the specimen size is determined by the supplier. The specimen shall include parent metal, heat-affected zone and weld metal. After the specimen has been cut, any high temperature or deformation associated with cutting that affects 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 transverse surface shall be polished so as to be suitable for examination at 500 times magnification. The etching solution may be prepared by adding 40 g of reagent-grade sodium hydroxide to 100 g of distilled water. The polished specimen is etched at 1 V to 3 V direct current for 5 s to 60 s; with platinum as the negative electrode and under these conditions any detrimental intermetallic phase appears yellow while the ferrite darkens, then turns brown and darkens further. After etching, the specimen shall be washed thoroughly with hot water, acetone or alcohol and air dried.

A.2.1.3 The whole etched surface shall be examined under the metallurgical microscope at 500 times. Specimens containing a weld shall be examined over all areas of the specimen, that is, the weld area, the heat-affected zone and the parent metal. The etched structures are classified as: unaffected structure (Figure A.1), in which the ferrite has been etched, there is no detrimental intermetallic phase and the phase boundaries are smooth; possibly affected structure (Figure A.2), in which the ferrite has been etched and free structures that may be detrimental intermetallic phases are shown, the phase boundaries possibly appearing slightly wavy; affected structure (Figure A.3), in which detrimental intermetallic phases appear quickly during etching, before or at the same time as the ferrite darkens; and centreline structure (Figure A.4), in which a continuous or discontinuous intermetallic phase is observed in the area at half the product thickness, affected structure showing segregation being present or absent outside that area.

A.2.1.4 Table A.1 divides these four etched structures into acceptable and unacceptable etched structures. The extractor did not preserve the column boundaries of Table A.1, so which structures fall in which column is not reproduced here.

A.2.2 Before the ferric chloride corrosion test, the sodium hydroxide etch test of method A may be used as a rapid screen: specimens that show an unaffected structure in method A need not undergo the ferric chloride corrosion test of method B, and all other specimens shall undergo it. The apparatus comprises a 1 000 mL glass beaker, a 1 000 mL long-form or conical flask, a wide-necked or 50 mm diameter test tube or another suitable vessel; a suitably shaped glass support that keeps the specimen in the middle of the test solution; and a water or oil bath at constant temperature. The test solution is prepared by dissolving 100 g of reagent-grade ferric chloride hexahydrate in 900 mL of distilled water, giving about 6 % ferric chloride by mass, and is filtered through glass wool or filter paper to remove insoluble particles; before the test the pH is adjusted to about 1.3 by adding hydrochloric acid or sodium hydroxide as required.

A.2.2.4 The dimensions of the specimen are measured with a vernier caliper and the total area and effective test area are calculated; the total surface area shall be more than 10 square centimetres. The specimen is cut to a size convenient for testing and its surface shall include the full thickness of the product, or at least more than half the thickness for particularly thick products. After cutting, any high temperature or deformation associated with cutting that affects 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 specimen surface shall not be passivated with nitric, citric or phosphoric acid, nor pickled with hydrofluoric acid or the like. The finished specimen shall be cleaned with magnesium oxide paste or a similar substance, rinsed with water, immersed in alcohol or acetone and air dried; it is then weighed to 0.1 mg or better and kept in a dry container until use.

A.2.2.5 The volume of ferric chloride solution used shall be at least 20 mL per square centimetre of specimen surface area. Table A.2 gives the test temperature and the acceptance criterion for each steel: for S22253 (022Cr22Ni5Mo3N) and for S22053 (022Cr23Ni5Mo3N), a test temperature of 25 °C plus or minus 1 °C for the parent metal and 22 °C plus or minus 1 °C for the weld; for S25073 (022Cr25Ni7Mo4N), S27603 (022Cr25Ni7Mo4WCuN) and S25554 (03Cr25Ni6Mo3Cu2N), a test temperature of 40 °C plus or minus 1 °C for the parent metal. In every case the corrosion rate shall be not more than 10 milligrams per square decimetre per day. The test period is 24 h. At the end of the 24 h period the specimen is removed from 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 solution and then dried in air. The specimen is weighed to 0.1 mg or better and kept for any retest.

A.2.2.6 The corrosion rate is expressed as the mass loss per unit area and unit time and is calculated by Formula (A.1), in which the masses of the specimen before and after the test are in milligrams, the total area of the specimen is in square decimetres and the test time is in days. Unless otherwise stated, the calculated corrosion rate shall not exceed 10 milligrams per square decimetre per day. If a specimen shows a corrosion rate above that value, two new specimens may be taken from the same product and tested again, the results complying with the same limit. A product that fails the ferric chloride corrosion test may be solution treated once and resampled for testing.