GB/T 19228.1-2024Stainless steel press-fitting assemblies - Part 1: Press-fittings (English PDF)

1 Scope

1 The document lays down the classification and designation, structural types and dimensions, technical requirements, tests, inspection and the packaging, transport and storage of stainless steel press-fittings, referred to below as fittings.

1 It applies to the design, manufacture and acceptance of press-fittings of nominal size not greater than DN100 and nominal pressure not greater than PN25 for stainless steel pipework carrying drinking water, piped direct drinking water, drainage, domestic hot water, cold water, sea water, fuel gas, medical gases and similar media.

3 Terms and definitions

3.1 Press jointing is a way of joining pipework in which a socket fitting carrying a special seal is used and the mouth of the pipe is pressed with a dedicated tool so as to seal and secure the joint. According to the form of the end, press jointing is divided into the S type and the D type.

4 Classification and designation

4.1.1 By the way the socket end is joined, fittings fall into two classes: the S type, in which the socket end of the fitting has an extended straight section, and the D type, in which it has none.

4.1.2 The kinds, forms and codes of the fittings are set in Table 1, which gives the code CAP for the cap, C for the equal coupling, CR for the reducing coupling, T for the equal tee, TR for the reducing tee, 90E-A and 90E-B for the A and B forms of the 90 degree elbow, 45E-A and 45E-B for the A and B forms of the 45 degree elbow, ITC for the female thread adaptor, ETC for the male thread adaptor and KF for the press flange adaptor. Two notes explain that an A-type press fitting has a socket at both ends of the joint while a B-type press fitting has a socket at one end and a spigot, that is a plain pipe end, at the other.

4.2 The basic parameters of the fittings are set in Table 2. The nominal pressure is not greater than PN16 for D-type fittings and not greater than PN25 for S-type fittings, and the design pressure not greater than 1.6 MPa and 2.5 MPa respectively. The table also gives, for each kind of fitting and each end type, the range of nominal sizes covered, but in the extracted text the size ranges are run together and cannot be matched to their rows with confidence, so they are not reproduced here.

4.3.1 The product designation is made up of the product code, the socket end connection type and series, the nominal size or pipe thread size, the material code such as S30408 or S31608, and the number of the document. Three examples are given, of an S-type series I equal coupling of nominal size DN20 in 06Cr19Ni10, of an S-type series II reducing tee in 06Cr17Ni12Mo2, and of a D-type male thread adaptor in 022Cr17Ni12Mo2; in the last two the size and thread designations are damaged in the extracted text.

4.3.2 Fittings that have passed inspection are to be marked with the trademark of the manufacturer, the size of the fitting and the material code.

5 Structural types and dimensions of the fittings

5.1 The structural type of the S-type socket is shown in Figure 1 a) and its basic dimensions are set in Table 3; the structural type of the D-type socket is shown in Figure 1 b) and its basic dimensions are set in Table 4. Figure 1 labels the body and the O-ring rubber seal. Table 3 is illegible in the extracted text and its dimensions are therefore not reported. Table 4 gives, for the nine nominal sizes from DN15 to DN100, the pipe outside diameter, the minimum wall thickness of the fitting, the socket bore, the bore and the outside diameter at the socket end and the socket length, all in millimetres and with their tolerances.

5.2 to 5.10 The structural types of the cap, the equal coupling, the reducing coupling, the equal tee, the reducing tee, the 90 degree elbow, the 45 degree elbow, the female thread adaptor and the male thread adaptor are shown in Figures 2 to 10, one figure for each with an S-type and a D-type part, and the elbows shown in both their A and their B form. Their basic dimensions are set in Tables 5 to 22, an S-type table and a D-type table for each kind, the S-type tables giving the pipe outside diameter and the structural length for the series I and the series II fittings side by side, and the D-type tables giving a single pipe outside diameter and structural length. The tee tables add the structural height of the branch, the elbow tables give the structural length both for the end with a socket and for the end without, and the thread adaptor tables add the pipe thread size, which is damaged in the extracted text wherever the size includes a fraction of an inch.

5.11 The structural type of the press flange adaptor is shown in Figure 11, with an S-type and a D-type part, and its basic dimensions are set in Tables 23 and 24, which give the pipe outside diameter and the length of the pressed connecting piece for the sizes DN15 to DN100. The dimensions and technical requirements of the flange itself are to comply with GB/T 9124.1 and the related standards, and flanges of another form may be used by agreement between supplier and purchaser.

6 Technical requirements

6.1.1 The materials commonly used for the fittings are listed in Table 25 by unified numerical code and grade, namely S30408 or 06Cr19Ni10, S30403 or 022Cr19Ni10, S31608 or 06Cr17Ni12Mo2, S31603 or 022Cr17Ni12Mo2 and S11972 or 019Cr19Mo2NbTi. Where the fitting is extruded, the material is to comply with GB/T 19228.2, GB/T 3280 or GB/T 713.7; where it is stamped from strip, with GB/T 4237; where an adaptor is cast in stainless steel, with GB/T 2100; and where another material is used, its performance is to be not lower than the requirements of the document.

6.1.2 The material of the O-ring rubber seal is to comply with GB/T 19228.3 and with Annex A.

6.2 The appearance of the fitting is to be clean and smooth and the weld surface free of cracks, pores, undercut and similar defects. Slight mould marks are allowed on the outer surface, but there is to be no obvious unevenness and no scratch deeper than the negative wall thickness tolerance, and the depth of a longitudinal scratch is not to exceed 10% of the nominal wall thickness.

6.3 The dimensional tolerances of the fittings are to comply with Tables 3 to 24, the thinned sections of elbows and tees are to meet the minimum wall thickness requirement, the internal and external threads of the adaptors are to comply with GB/T 7306.1, the dimensions of the O-ring rubber seals are to comply with Annex A, the dimensions of the thin-wall stainless steel tube to be joined are to comply with Annex B, and the jaw dimensions of the pressing tools for S-type fittings are given in Annex C.

6.4 As to the delivery condition, fittings are to be solution treated after machining and welding, and pickled and passivated after solution treatment, except that fittings whose surface has been bright heat treated need not be pickled and passivated; delivery in another condition is allowed by agreement between supplier and purchaser.

6.5.1 After the intergranular corrosion test of 7.3.1 the fitting is to show no cracking or flaking, and after the salt spray test of 7.3.2 its surface is to show no rusting.

6.5.2 and 6.5.3 After the hydrostatic test of 7.4 the fitting is to be free of leakage and permanent deformation, and after the air tightness test of 7.5 free of leakage.

6.5.4 For the performance of the assembled joint, the pressure test of 7.6.1 is to leave the assembly free of leakage and permanent deformation; the negative pressure test of 7.6.2 is to leave a loss of vacuum of not more than 5 kPa; the pull-out test of 7.6.3 is to give a pull-out force greater than the minimum pull-out resistance of Table 26, which in kilonewtons requires for the S type and the D type respectively 1.9 and 1.2 at DN10, 3.1 and 1.98 at DN15, 5.4 and 3.46 at DN20, 7.0 and 4.5 at DN25, 10.0 and 6.42 at DN32, 12.7 and 8.12 at DN40, 15.2 and 9.72 at DN50, 38.3 and 24.5 at DN65, 45.3 and 29.0 at DN80 and 54.7 and 35.0 at DN100, with a note that the permanent displacement within the specified range of pull-out force is not to exceed 1.0 mm; the temperature change test of 7.6.4, the water pressure bending deflection test of 7.6.5, the water pressure vibration test of 7.6.6 and the pressure impact test of 7.6.7 are each to leave the joints free of leakage and of any other abnormality, the last two also free of detachment.

6.5.5 and 6.5.6 Fittings used to convey piped direct drinking water and drinking water are to meet the hygiene requirements of GB/T 17219 and the related documents, and fittings used for fuel gas and medical gases are to meet the performance requirements and test methods of the related documents.

6.6 The joining and installation of fittings and pipes are to comply with the related documents.

7 Test methods

7.1 and 7.2 The appearance is examined visually in daylight or artificial light, a five times magnifier being allowed, and the dimensions are measured with a caliper or micrometer of adequate accuracy.

7.3 The intergranular corrosion test is carried out by method E of GB/T 4334-2020, and the salt spray test by the neutral salt spray procedure of GB/T 10125 for a duration of 240 h.

7.4 For the hydrostatic test the ends of the fitting are blanked off, tap water is admitted and the pressure is held for not less than 5 s, the test pressure being not lower than 2.5 MPa for D-type fittings and not lower than 3.75 MPa for S-type fittings; the result is checked against 6.5.2.

7.5 For the air tightness test the fitting is mounted on the test rig and charged with compressed air, the pressure being held for not less than 5 s. For fittings used with gaseous media the test pressure is 1.05 times the design pressure and not lower than 0.6 MPa, and for fittings used with liquid media it is 0.6 MPa; the result is checked against 6.5.3.

7.6.1 For the pressure test the ends of the fitting are press jointed to lengths of 200 mm of thin-wall stainless steel tube to form one test assembly, which is filled with water and vented, and the internal pressure is raised gradually to not less than 2.5 MPa for D-type fittings and not less than 3.75 MPa for S-type fittings and held for 1 min.

7.6.2 For the negative pressure test three reducing fittings of different nominal size are press jointed to lengths of 200 mm of equal-diameter thin-wall stainless steel tube to form one test assembly, which is fitted with a vacuum gauge of accuracy class not lower than 1.5. At a laboratory temperature of 20 °C plus or minus 5 °C the assembly is evacuated to -80 kPa, sealed off on its own and held for 1 h.

7.6.3 For the pull-out test, shown in Figure 12 with its pressure source, tensile testing machine, fitting and pipe, the end of the fitting is press jointed to a length of 300 mm of thin-wall stainless steel tube to form one test assembly, the pipe is charged with air at 0.6 MPa, the two ends of the assembly are clamped in the tensile testing machine and the assembly is pulled at 2 mm/min, the maximum pull-out force at the moment leakage appears being taken as the result.

7.6.4 For the temperature change test, shown in Figure 13, water at 20 °C plus or minus 5 °C and hot water at 93 °C plus or minus 5 °C are used and 1000 cycles are run at an internal pressure of 2.5 MPa plus or minus 0.25 MPa, one cycle lasting 20 min with 10 min of cold and 10 min of hot water and the changeover completed within 1 min.

7.6.5 For the water pressure bending deflection test, shown in Figure 14, the end of the fitting is press jointed to a length of 800 mm of thin-wall stainless steel tube to form one test assembly, the pressure gauge used being of accuracy class not lower than 1.5. The assembly is filled with water and vented and the internal pressure is kept constant at 2.5 MPa for D-type fittings and 3.75 MPa for S-type fittings during the test, while the load F is applied as shown in the figure until the bending angle reaches the value required by Table 27, which is then held for 1 min. The horizontal distance from the support point to the centre of the fitting is 500 mm. In Table 27 a bending angle of 30 degrees is required for the sizes DN10, DN15, DN20, DN25 and DN32; the table also sets angles of 20 degrees and 15 degrees for the sizes DN40, DN50, DN65, DN80 and DN100, but in the extracted text those two angles cannot be matched to their sizes with confidence and the assignment is therefore not reported.

7.6.6 For the water pressure vibration test, shown in Figure 15, the fitting is press jointed to lengths of thin-wall stainless steel tube of 500 mm or more to form one test assembly, which is filled with water and vented and pressurised to 2.5 MPa for D-type fittings and 3.75 MPa for S-type fittings, and vibration is applied under the conditions of Table 28 for one million cycles. Table 28 sets an amplitude of plus or minus 2.5 mm together with a vibration frequency of 600 strokes per minute for the sizes DN15 to DN32, 200 strokes per minute for DN40 to DN50 and 60 strokes per minute for DN65 to DN100.

7.6.7 For the pressure impact test both ends of the fitting are press jointed to lengths of 500 mm of thin-wall stainless steel tube to form one test assembly, which is filled with water and then raised to 2.5 MPa for the D type or 3.75 MPa for the S type and lowered again to near 0 MPa, the operation being completed within 10 s and taken as one cycle, and 1500 cycles being run.

7.7 For the hygiene test, fittings used to convey piped direct drinking water and drinking water are cleaned and soaked before the test and then tested according to the related provisions of GB/T 17219.

8 Inspection

8.1 The inspection of fittings is divided into works inspection and type inspection.

8.2 Every fitting is to pass the inspection of the quality inspection department of the manufacturer before it leaves the works. The items and their order are given in Table 29. Material is inspected batch by batch according to the melting heat number of the raw material; appearance and dimensions are inspected 100%; and either the hydrostatic test or the air tightness test, at choice, is applied 100%. Works inspection is judged as follows: where every item conforms, the works inspection passes; where the material inspection fails, the works inspection fails; and where any other item fails, a double sample is taken and retested, the works inspection passing if the retest conforms and failing if any item still fails.

8.3 Type inspection is to be carried out when a product is first made or its manufacture is transferred to another works, when after regular production the process has been changed considerably in a way that may affect the performance of the product, when a higher quality supervisory body or a user asks for it, at least once every three years during normal production, and in other cases. The items and their order are given in Table 29, three samples of different sizes being taken from among fittings of the same form. Table 29 lists fifteen items, namely material, appearance, dimensions, the intergranular corrosion test, the salt spray test, the hydrostatic test, the air tightness test, the pressure test, the negative pressure test, the pull-out test, the temperature change test, the water pressure bending deflection test, the water pressure vibration test, the pressure impact test and the hygiene test, with the clause of the test method for each and a mark showing whether the item belongs to type inspection, to works inspection or to both. Type inspection is judged by the same three rules as works inspection.

9 Packaging, transport and storage

9.1 Fittings that have passed inspection are to be placed in clean sealed plastic bags and packed in paper or wooden cases, each case carrying a quality certificate or certificate of conformity.

9.2 The case is to bear the name of the product, the quantity, the mass, the dimensions of the case, the designation, the name of the manufacturer and a moisture warning, or else to meet the relevant provisions of GB/T 191.

9.3 and 9.4 Cased products may be carried by any means of transport provided they are not directly exposed to rain or snow, and are not to be violently knocked, thrown, dropped, rolled or dragged during handling; they are to be stored in a dry, clean place free of corrosive gases, and not stacked in disorder or mixed with other goods.

9.5 Each batch of fittings is to be accompanied by a quality certificate covering at least the name of the manufacturer, the name of the product, the size of the product and the number of the document, the material grade, the results of the inspections required by the order contract and by the product standard together with the stamp of the quality department of the works, and the date of packing.

A Annex A (normative) Additional requirements for the O-ring rubber seals used in stainless steel press-fittings

A.1 The structural type of the O-ring rubber seal used in stainless steel press-fittings is shown in Figure A.1. The basic dimensions, tolerances and hardness of the seals for S-type fittings are set in Table A.1, which gives for each nominal size from DN10 to DN100 the inside diameter of the seal for the series I and the series II fitting with its tolerance, the cross-sectional diameter for each series with its tolerance, and the hardness, the hardness being 65 IRHD to 75 IRHD throughout the table.

A.1.3 The basic dimensions and tolerances of the O-ring rubber seals for D-type fittings are to comply with Table 1 of GB/T 19228.3-2012.

A.2 The requirements, testing and inspection, inspection rules, marking, packaging, storage and transport of the O-ring rubber seals are to follow GB/T 19228.3-2012.

B Annex B (normative) Additional requirements for the thin-wall stainless steel tube joined by stainless steel press-fittings

B.1 The basic dimensions and tolerances of the tube are set in Table B.1, which gives for each nominal size the outside diameter and nominal wall thickness for the S type and for the D type, the permitted deviation on the outside diameter and the permitted deviation on the wall thickness, the last being plus or minus 10% of the nominal wall thickness throughout. Tube of another outside diameter or wall thickness may be supplied by agreement between supplier and purchaser at the request of the purchaser.

B.2 The technical requirements of the tube are to comply with GB/T 19228.2 and GB/T 713.7. The material grades of the tube and the range of use of each are set in Table B.2: S30408 or 06Cr19Ni10 for piped direct drinking water, drinking water, medical gases, fuel gas and domestic hot water; S30403 or 022Cr19Ni10 for piped direct drinking water, cold water and domestic hot water; S31608 or 06Cr17Ni12Mo2 for sea water and for service more corrosive than that of S30403; S31603 or 022Cr17Ni12Mo2 for service more corrosive than that of S31608; S11972 or 019Cr19Mo2NbTi for service in which the medium contains a relatively high chloride ion content; S12362 or 019Cr23MoTi for chloride resistance beyond that of S11972; and S12361 or 019Cr23Mo2Ti for chloride resistance beyond that of S12362, the last two being subject to agreement between supplier and purchaser.

C Annex C (informative) Jaw dimensions of the pressing tools used for S-type stainless steel press-fittings

C.1 The annex applies to the jaws of the pressing tools used for S-type stainless steel press-fittings, and the jaws of tools for other fittings may also be designed by reference to it.

C.2 The structural types of the jaws are shown in Figure C.1, which gives an arc-shaped jaw and a trapezoidal jaw. Their basic dimensions are set in Table C.1, which is illegible in the extracted text and whose dimensions are therefore not reported.