NB/T 10938-2022Coil-wound heat exchanger (English PDF)

Foreword

This document was issued on 13 May 2022 by the National Energy Administration of the PRC and takes effect on 13 November 2022.

It is a NB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

It is classified under ICS 27.060.30, Chinese classification J75.

This document was drafted in accordance with the rules given in GB/T 1.1-2020 Directives for standardization - Part 1: Rules for the structure and drafting of standardizing documents.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.

This document was proposed by and is under the jurisdiction of the National Technical Committee on Boilers and Pressure Vessels of Standardization Administration of China (SAC/TC 262).

The drafting of this document was organized by the Heat Exchanger Subcommittee of the National Technical Committee on Boilers and Pressure Vessels of Standardization Administration of China (SAC/TC 262/SC 5).

Drafting organizations of this document: Shanghai Lanbin Petrochemical Equipment Co., Ltd., China Special Equipment Inspection and Research Institute, SINOPEC Engineering Incorporation, SINOPEC Luoyang Engineering Co., Ltd., Xi'an Jiaotong University, Hefei General Machinery Research Institute Co., Ltd., Tianjin University, Kaifeng Air Separation Group Co., Ltd., Zhenhai Petrochemical Construction and Installation Engineering Co., Ltd., Wuhan Donghai Petrochemical Heavy Equipment Co., Ltd., Gansu Lanke Petrochemical High-Tech Equipment Co., Ltd., Shanghai Nuclear Engineering Research and Design Institute Co., Ltd., Zhejiang Jiuli Hi-Tech Metals Co., Ltd., Zhejiang Zhongda Special Steel Co., Ltd., Wuxi Tengyue Special Steel Tube Co., Ltd., Hangzhou Hongze New Energy Co., Ltd., Shanghai Petrochemical Heat Exchange Equipment Engineering Technology Research Center, Zhongte Inspection Group Co., Ltd.

Chief drafters of this document: Ma Yiming, Chen Zhiwei, Zhang Yingkai, Gu Yuezhang, Bai Bofeng, Chen Yongdong, Liu Fulu, Tan Wei, Yu Wang, Zhang Xian'an, Li Mingkai, Zhao Guodong, Jiao Ming, Shao Yu, Wu Liyang, Wang Zhibiao, Zhou Hongda, Su Houde, Xing Ling, Chen Zhanyang, Zhou Wenxue, Zhang Yanfeng, Zhang Songsong.

This document is issued for the first time.

1 Scope

NB/T 10938-2022 is the Chinese standard for coil-wound heat exchangers in austenitic stainless steel, with design pressure up to 10 MPa. A coil-wound exchanger carries many layers of small tubes wound helically around a central core inside a pressure shell: the arrangement packs an enormous surface into a compact vessel and handles several streams at once with close temperature approach, which is why it is the workhorse of LNG liquefaction, air separation and low temperature methanol washing. This is the first edition of the standard. It sets the scope, the normative references and the defined terms, then the general requirements, including the designation system by which a unit is identified. It covers the materials for the shell, the tube bundle, the tubesheets and the core, with their acceptance and the low-temperature toughness required. Design follows: the pressure design of the shell and the tubesheets, the winding geometry of the bundle with its pitch, angle and spacers, the thermal and hydraulic design, the supports and the allowance for thermal movement between bundle and shell. Fabrication covers tube winding and its tolerances, tube-to-tubesheet welding, the assembly of the bundle into the shell, and cleanliness. Inspection and testing, including pressure and leak testing of each stream, then marking, packing, installation, operation and maintenance close the document.

1.1 This document specifies the requirements for materials, design, manufacture, inspection, acceptance, installation, use and maintenance of coil-wound heat exchangers made of austenitic stainless steel (hereinafter referred to as heat exchangers).

1.2 This document is applicable to heat exchangers with a design pressure not higher than 10 MPa.

1.3 The design temperature to which this document applies shall not exceed the permissible service temperature range of the austenitic stainless steels listed in GB/T 150.2-2011.

1.4 This document is not applicable to the following cases: a) media that are prone to fouling, coking or deposition, with a risk of blockage; b) cases where there is a risk of intergranular corrosion.

1.5 Boundary of the heat exchanger, item a): the connection between the heat exchanger body and the external piping, namely 1) the groove end face of the first circumferential joint for welded connections; 2) the first flange sealing face for flanged connections; 3) the end face of the first threaded joint for threaded connections; 4) the first sealing face for connections made with special connectors or pipe fittings.

1.5 b) Pressure-retaining heads, flat covers and their fasteners of nozzles, manholes, handholes and the like.

1.5 c) The connecting welds between non-pressure parts and pressure parts.

1.5 d) Non-pressure parts directly attached to the heat exchanger, such as supports and pads.

1.5 e) Overpressure relief devices mounted directly on the heat exchanger.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.

GB/T 150-2011 (all parts) Pressure vessels (including Amendment No. 1)

GB/T 151-2014 Heat exchangers

GB/T 27698.1 Performance test methods for heat exchangers and heat transfer elements - Part 1: General requirements

GB/T 27698.8 Performance test methods for heat exchangers and heat transfer elements - Part 8: Industrial calibration of heat exchangers

NB/T 10558 Coating and transport packing for pressure vessels

NB/T 47010 Stainless and heat-resisting steel forgings for pressure equipment

NB/T 47019 (all parts) Technical conditions for ordering tubes for boilers and heat exchangers

NB/T 47041 Vertical vessels supported by skirt

NB/T 47065 (all parts) Supports for vessels

JB 4732 Steel pressure vessels - Design by analysis (confirmed in 2005)

3 Terms and definitions

For the purposes of this document, the terms and definitions given in GB/T 150.1-2011 and GB/T 151-2014 and the following apply.

3.1 coil-wound heat exchanger: general term for a shell-and-tube heat exchanger in which the heat exchange tubes are spirally wound on a mandrel, one or more tube-side media flow inside the spirally wound tubes, and heat is exchanged through the tube wall with the shell-side medium.

3.2 mandrel: the component made up of the core shaft on which the heat exchange tubes are wound and its supports.

3.3 core: the component made up of the mandrel, heat exchange tubes, spacers, bundles shell and other parts.

3.4 spacer: general term for flat spacer strips, profiled spacer strips, tube hoops and other parts used to fix the position of the heat exchange tubes.

3.5 spiral angle: the angle between the tangent to the helix of a heat exchange tube and the cross section of the equipment.

3.6 bundles shell: the thin-walled cylinder wrapped around the outermost layer of the tube bundle.

3.7 bundle: the structure made up of the tubesheets and the core.

3.8 single-flow: a tube-side arrangement carrying only one medium.

3.9 multi-flow: a tube-side arrangement carrying two or more media.

3.10 integrated tubesheet heat exchanger: a heat exchanger with a single tube-side flow, in which the heat exchange tube holes are distributed over the whole tubesheet.

3.11 integrated tubesheet heat exchanger with different tube layout areas: a heat exchanger with multiple tube-side flows, in which the tube holes for each medium are grouped in different areas of one tubesheet.

3.12 separated tubesheet heat exchanger: a heat exchanger in which the tube holes for each tube-side medium are grouped on different tubesheets.

4 General requirements

4.1.1 The heat exchanger shall comply with this document; matters not specified herein shall be in accordance with the relevant provisions of GB/T 151-2014.

4.1.2 The design and manufacturing organizations of the heat exchanger shall establish a sound and effectively operating quality assurance system.

4.1.3 Heat exchangers or pressure parts that cannot be designed and calculated in accordance with GB/T 150.3-2011, this document and the relevant standards should be designed by the methods specified in 4.1.6 of GB/T 150.1-2011.

4.2.1 Qualification. Design and manufacturing organizations of heat exchangers falling within the scope of the Supervision Regulation on Safety Technology for Stationary Pressure Vessels shall hold the corresponding special equipment production licence.

4.2.2.1 Responsibilities of the purchaser or design principal. The purchaser or design principal shall submit to the design organization, in writing, design conditions (user design specification) containing at least: a) the main standards and codes on which the design is based; b) operating parameters, including working pressure, working temperature range, flow rate, liquid level, nozzle loads and cyclic loads; c) place of use and its natural conditions, including ambient temperature, seismic fortification intensity and wind load; d) medium composition and characteristics; e) expected service life; f) geometric parameters and nozzle orientation; g) other conditions necessary for the design.

4.2.2.2 Responsibilities of the design organization, item a): it shall be responsible for the correctness and completeness of the design documents.

4.2.2.2 b) The design documents of the heat exchanger shall include at least the strength calculation report, design drawings, technical conditions for manufacture, the risk assessment report (when required by the relevant regulations or by the design principal), and the installation, use and maintenance instructions.

4.2.2.2 c) The general design drawing of heat exchangers within the scope of the Supervision Regulation on Safety Technology for Stationary Pressure Vessels shall bear the special seal for pressure vessel design.

4.2.2.2 d) All design documents of the heat exchanger shall be kept for the design service life.

4.2.2.3 Responsibilities of the manufacturing organization, item a): manufacture shall follow the requirements of the design documents; where the original design needs to be modified, written consent of the original design organization shall be obtained and the modified locations shall be recorded in detail.

4.2.2.3 b) Before manufacture, a complete quality plan shall be prepared, including at least the process control points, the inspection items and the acceptance criteria for the heat exchanger or its parts.

4.2.2.3 c) During manufacture and after completion, the inspection department shall carry out all examinations and tests of the heat exchanger as specified in the standards, drawings and quality plan, issue the corresponding reports and be responsible for their correctness and completeness.

4.2.2.3 d) After passing inspection, a product quality certificate shall be issued.

4.2.2.3 e) For each heat exchanger manufactured, at least the following technical documents shall be kept for the design service life: 1) quality plan; 2) manufacturing process drawings or process cards; 3) product quality certification documents; 4) welding procedure and heat treatment procedure documents; 5) records of the inspections and tests that the standard allows the manufacturer to select; 6) records of examinations, inspections and tests during manufacture and after completion; 7) as-built drawings.

4.3.1.1 The purchaser or design principal shall submit process design conditions to the design organization in writing, containing at least: a) operating data under different operating cases, including flow rate, vapour fraction, temperature, pressure and heat duty; b) medium composition or physical property data; c) allowable pressure drop; d) installation requirements such as geometric parameters and nozzle orientation.

4.3.1.2 See Annex A for the process data sheet of the heat exchanger.

4.3.2 Selection and calculation. In addition to economy, the selection and calculation of the heat exchanger shall meet the following requirements: a) safety, heat transfer and energy efficiency requirements; b) installation, operation and maintenance requirements.

4.4.1.1 The following loads shall be considered in design: a) internal pressure, external pressure or maximum pressure difference; b) liquid column static pressure, which may be neglected when it is less than 5% of the design pressure.

4.4.1.2 Where necessary, the following loads shall also be considered: a) the self-weight of the heat exchanger and the gravity load of the contents under normal operating conditions or during the pressure test; b) the gravity loads of attached equipment, insulation, lining, piping, ladders, platforms and the like; c) wind and seismic loads; d) reaction forces of supports and other types of supporting parts; e) forces from connected piping and other components; f) thermal stresses caused by temperature gradients; g) impact loads, including impact loads caused by sharp pressure fluctuations and reaction forces from fluid impingement; h) forces during manufacture, transport or lifting.

4.4.2 a) Design pressure or calculation pressure: where an overpressure relief device is installed on the heat exchanger, the design pressure shall be determined in accordance with Annex B of GB/T 150.1-2011.

4.4.2 b) The design pressure of each side (pressure chamber) of the heat exchanger shall be determined separately according to its own most severe operating case.

4.4.2 c) Where the heat exchanger operates under negative pressure, the maximum pressure difference between inside and outside that may occur under normal operating conditions shall be considered when determining the calculation pressure of the parts.

4.4.2 d) The design pressure of the vacuum side shall be taken as external pressure; where a safety control device (such as a vacuum relief valve) is installed, the design pressure shall be the lower of 1.25 times the maximum pressure difference between inside and outside and 0.1 MPa; where no safety control device is installed, 0.1 MPa shall be taken.

4.4.2 e) Parts subjected simultaneously to the pressures of several sides (pressure chambers) may be designed for the pressure difference only if it can be guaranteed that the set pressure difference is not exceeded over the whole service life; otherwise the calculation pressure shall be determined from the design pressure of each side and the most severe possible pressure combination shall be considered. When designing for the pressure difference, its value shall also account for the maximum pressure difference that may occur during the pressure test, the design pressure difference shall be stated in the design documents, and requirements for maintaining the pressure difference during the pressure test shall be given.

4.4.3 a) Design temperature: the design temperature of each side (pressure chamber) shall be determined separately according to its own most severe operating case; where the metal temperatures of different parts differ in operation, separate design temperatures may be set.

4.4.3 b) The design temperature shall not be lower than the maximum temperature the part metal may reach in operation; for metal temperatures below 0 degrees C, the design temperature shall not be higher than the minimum temperature the part metal may reach; in no case shall the surface temperature of the part metal exceed the permissible service temperature of the material.

4.4.3 c) For parts exposed to media temperatures on both sides, the design temperature shall be determined from the metal temperature.

4.4.3 d) The metal temperature of a part may be determined by: 1) heat transfer calculation; 2) measurement on similar heat exchangers already in service; 3) evaluation from the medium temperature combined with external conditions.

5 Materials

5.1.1 The selection of materials for the heat exchanger shall take into account the service conditions (including design temperature, design pressure and medium characteristics), the weldability and workability of the materials, and economic rationality.

5.1.2 The general requirements for materials, the technical requirements for steels and their limits of application (grades, pressure and temperature, etc.) shall comply with the standards referenced in this document.

5.1.3 The steel grades and their standards, additional technical requirements, limits of application and allowable stresses of materials for pressure parts shall comply with GB/T 150.2-2011; reference values of high-temperature properties are given in Annex B of GB/T 150.2-2011; materials for low-temperature pressure vessels shall comply with Annex E of GB/T 150.3-2011.

5.1.4 In addition to the relevant codes and standards, materials for the heat exchanger shall also meet the requirements of the design technical documents.

5.2.1 In addition to NB/T 47019, the technical conditions for ordering heat exchange tubes shall meet the requirements of the design documents.

5.2.2 Heat exchange tubes shall have no circumferential butt welds.

5.2.3 The hardness of the parent metal of welded tubes shall not exceed 90 HRB or 210 HV.

5.2.4 Where repeated deformation would cause unacceptable cold work hardening of the tube material or insufficient corrosion resistance in the medium, straight tubes shall be supplied. For coiled tubes, the minimum allowable coil diameter shall be controlled according to the material, size and design requirements, and should generally be not less than 1 400 mm. The roundness deviation of straight and coiled tubes shall not exceed 0.16 mm.

5.2.5 Heat exchange tubes shall be subjected one by one to a hydrostatic test or an underwater air tightness test in accordance with NB/T 47019.

5.2.6 Heat exchange tubes shall be adequately protected against contamination during manufacture, transport and storage.

5.3.1 Steel forgings for the heat exchanger shall comply with NB/T 47010.

5.3.2 Forgings used for tubesheets, shells, flanges, nozzles and the like shall comply with Chapter 6 of GB/T 150.2-2011, and the forging class shall not be lower than class II.

5.4 Internals. Non-pressure internal parts of the heat exchanger, including the mandrel, tube spacers and bundles shell, shall have strength, rigidity and corrosion resistance appropriate to the medium conditions so as to meet the design service life.

6 Design

6.1.1 According to the characteristics of the tubesheet, heat exchangers are classified into three structural types; the types and their codes are given in Table 1, and the structure, main parts and their names of type I, II and III heat exchangers are shown in Figure 1, Figure 2 and Figure 3 respectively.

Table 1 Classification of heat exchanger structural types: integrated tubesheet heat exchanger - code I; integrated tubesheet heat exchanger with different tube layout areas - code II; separated tubesheet heat exchanger - code III.

6.1.2 Model designation. The heat exchanger model is expressed by the structural type, nominal diameter, overall height of the equipment (overall length for horizontal equipment, with L placed before the length in the model), tube-side design pressures, shell-side design pressure and number of tube-side flows, in the form CE I DN x H(L) - pt1/pt2/.../ptn/ps - N, where CE is the code for a coil-wound heat exchanger, I is the structural type code, DN is the nominal diameter in mm, H (or L) is the overall height (or overall length) in mm, pt1 and pt2 are the design pressures of tube side 1 and tube side 2 in MPa, ps is the shell-side design pressure in MPa and N is the number of tube-side flows.

Example 1: integrated tubesheet heat exchanger, nominal diameter 2 200 mm, overall height 8 000 mm, tube-side design pressure 4.0 MPa, shell-side design pressure 2.5 MPa, one tube-side flow: CE I 2 200x8 000-4.0/2.5-1.

Example 2: integrated tubesheet heat exchanger, nominal diameter 2 200 mm, horizontal arrangement, overall length 8 000 mm, tube-side design pressure 4.0 MPa, shell-side design pressure 2.5 MPa, one tube-side flow: CE I 2 200xL8 000-4.0/2.5-1.

Example 3: integrated tubesheet heat exchanger with different tube layout areas, nominal diameter 2 000 mm, overall height 9 000 mm, tube side 1 design pressure 4.0 MPa, tube side 2 design pressure 3.0 MPa, shell-side design pressure 1.6 MPa, two tube-side flows: CE II 2 000x9 000-4.0/3.0/1.6-2.

Example 4: separated tubesheet heat exchanger, nominal diameter 1 600 mm, overall height 10 000 mm, tube side 1 design pressure 1.6 MPa, tube side 2 design pressure 2.5 MPa, tube side 3 design pressure 4.0 MPa, shell-side design pressure 1.0 MPa, three tube-side flows: CE III 1 600x10 000-1.6/2.5/4.0/1.0-3.

Figure 1 Integrated tubesheet heat exchanger (I): a) vertical type, showing the nozzle, flange, channel head, channel shell, tubesheet, vent, shell head, mandrel support, mandrel, shell cylinder, lug support, heat exchange tubes, bundles shell, impingement plate, drain, tube hoop, spacer strip and support; b) horizontal type on saddle supports.

Figure 2 Integrated tubesheet heat exchanger with different tube layout areas (II).

Figure 3 Separated tubesheet heat exchanger (III), showing the impingement plate, slideway, lifting lug, mandrel support and skirt.

6.2.1 The channel consists of the channel shell, the head, the nozzle flanges and other parts; the head should be a formed (convex) head. The channel head and the channel shell may be connected by welding or by flanges.

6.2.2 The thickness calculation of the channel shell and head and the reinforcement calculation for openings in the channel shall comply with the relevant provisions of GB/T 150.3-2011.

6.2.3 For integrated tubesheet heat exchangers with different tube layout areas, the distance between the outer walls of any two adjacent channels shall be not less than 100 mm.