NB/T 11270-2023Titanium pressure vessels (English PDF)

Foreword

This document was issued on 26 May 2023 by the National Energy Administration of the PRC and takes effect on 26 November 2023.

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 23.020.30, Chinese classification J 74.

It replaces JB/T 4745-2002, which is superseded.

This document has been 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.

This document replaces JB/T 4745-2002, Titanium welded vessels. In addition to structural adjustments and editorial changes, the following main technical changes have been made with respect to JB/T 4745-2002:

a) the field of application has been modified, so that the body of the standard now applies to titanium pressure vessels (see Clause 1);

b) the necessary normative references have been adjusted according to the needs of the text (see Clause 2);

c) terms and definitions have been added (see Clause 3);

d) the basis for determining the allowable stress has been modified (see Table 1);

e) the provisions for the classification of welded joints have been modified (see 4.7.1);

f) a method for the combined gas and liquid pressure test has been added (see 4.8);

g) titanium material designations for pressure vessels have been added (see 5.1.3) and the upper limit of the design temperature of titanium materials has been adjusted to 315 degrees Celsius;

h) supplementary requirements for the room temperature mechanical properties of titanium plate, titanium tube, titanium forgings and titanium bar have been added (see 5.2.1, 5.3.2, 5.4.1 and 5.5.1);

i) requirements for welding consumables have been added (see 5.6);

j) the allowable stress tables for titanium materials have been recalculated and updated (see Table 7 to Table 10);

k) the external pressure stress coefficient B curves for titanium materials have been recalculated and updated (see Figure 1 to Figure 8), together with their corresponding tables (see Table 11 to Table 18);

l) the design requirements have been simplified by reference to other standards (see Clause 6);

m) the basis for the fabrication, inspection and acceptance of titanium vessels has been modified (see 7.1.1.1);

n) requirements for purchased finished titanium parts and components have been added (see 7.1.1.2);

o) requirements relating to risk prevention and control during the fabrication of titanium vessels have been added (see 7.1.5 and 7.1.6);

p) requirements for the re-examination of materials have been added (see 7.2.1);

q) the provisions relating to forming have been modified (see 7.3.1);

r) the requirements of the welding part have been modified and supplemented (see 7.4);

s) the requirements of the heat treatment part have been modified and supplemented (see 7.5);

t) the requirements of the part dealing with test coupons and test specimens have been modified and supplemented (see 7.6);

u) the requirements of the non-destructive testing part have been modified and supplemented (see 7.7);

v) the requirements of the part dealing with the pressure test and the leak test have been modified and supplemented (see 7.8);

w) requirements for the part dealing with the hot gas circulation test have been added (see 7.9);

x) the normative annex Titanium clad plate pressure vessels and titanium lined pressure vessels has been added (see Annex A); by reference to the applicable regulations the annex Rules for the qualification examination of welders of titanium vessels has been deleted; by reference to other standards the annexes Welding procedure qualification for titanium vessels and Mechanical property tests of product welded test plates of titanium vessels have been deleted;

y) the informative annexes Welding procedure specifications for titanium vessels (see Annex B), Designations and properties of titanium materials for pressure vessels (see Annex C) and Joint structures of titanium vessels, titanium clad plate vessels and titanium lined vessels (see Annex D) have been modified and supplemented.

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 has been 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 organizations that drafted this document are: Hefei General Machinery Research Institute Co., Ltd., Nanjing Baose Co., Ltd., Baoti Group Co., Ltd., China Petrochemical Engineering Construction Co., Ltd., China Special Equipment Inspection and Research Institute, Zhejiang University of Technology, Xian Younai Special Vessel Manufacturing Co., Ltd., Hefei General Special Material Equipment Co., Ltd., China Wuhuan Engineering Co., Ltd., Western Titanium Industry Co., Ltd., CNNC Baoti Zirconium Industry Co., Ltd. and Hangzhou Special Equipment Inspection and Research Institute.

The main drafters of this document are: Cui Jun, Du Yongqin, Feng Junning, Li Shengli, Chen Zhiwei, Fan Haijun, Sun Wancang, Wu Pijie, Chen Bingbing, Xu Pengcheng, Xu Caifu, Dai Yi, Li Xianjun, Hu Xukun and Liu Yanlei.

The successive editions of this document and of the document it replaces are as follows: first published in 2002 as JB/T 4745-2002; this is the first revision.

1 Scope

NB/T 11270-2023 governs pressure vessels made of titanium and titanium alloys, replacing JB/T 4745-2002 on welded titanium vessels and widening the scope to pressure vessels proper. Titanium is chosen where corrosion defeats stainless steel - chlor-alkali plant, seawater and brine service, bleaching and organic acid duty - and almost every rule in the document follows from how the metal behaves: it must be protected from oxygen, nitrogen and hydrogen pickup at temperature, it cannot be welded or handled with steel tooling without contamination, and its strength falls sharply as temperature rises. The standard sets the permitted grades of commercially pure titanium and titanium alloy and their allowable stresses, together with titanium-clad steel plate and the requirements for the bond. It covers the general requirements on design conditions, the design of shells, heads, openings and flanges, and the wall thickness calculation with the corrosion allowance appropriate to titanium. Fabrication is treated at length: forming and its temperature limits, cutting, cleanliness and segregation from ferrous contamination, welding procedure and welder qualification with the inert gas shielding and trailing shields required, heat treatment, and the inspection of the finished welds. Testing, marking and the documentation supplied on delivery close the document. It applies to the design, manufacture, inspection and acceptance of titanium pressure vessels in China.

1.1 This document specifies the requirements for the materials, design, fabrication, inspection and acceptance of titanium pressure vessels. It applies to single-layer plate-welded pressure vessels (including tube-made shells) whose shell is made entirely of titanium material. The requirements for the materials, design, fabrication, inspection and acceptance of titanium vessels operating at atmospheric pressure may also be taken as a reference from this document.

1.2 This document applies to titanium pressure vessels with a design pressure not greater than 35 MPa.

1.3 The titanium materials covered by this document have an upper design temperature limit of 315 degrees Celsius.

1.4 The design and calculation methods listed in this document apply to pressure-retaining components made entirely of titanium material. Those parts of a titanium pressure vessel that are made of non-titanium materials shall be designed and calculated in accordance with the corresponding product standards for those materials.

1.5 This document does not apply to the following pressure vessels:

a) vessels with a design pressure lower than 0.1 MPa and with a degree of vacuum lower than 0.02 MPa;

b) vessels governed by the Regulation on Safety Technology Supervision of Mobile Pressure Vessels;

c) pressure vessels used in military equipment, nuclear facilities, aerospace and aviation vehicles, railway locomotives, offshore installations and ships, and underground in mines;

d) pressure chambers that form an integral part of, or act as a component of, rotating or reciprocating mechanical equipment, such as pump casings, compressor casings, turbine casings, hydraulic cylinders and paper-making press rolls;

e) vessels heated directly by flame;

f) plate heat exchangers, spiral plate heat exchangers, air-cooled heat exchangers and cooling coils;

g) vessels whose volume (deducting the geometric volume of permanent internals) is less than 0.03 cubic metres, or whose inside diameter (for non-circular cross sections, the largest geometric dimension of the inner boundary of the cross section) is less than 150 mm;

h) vessels for which fatigue analysis is carried out.

1.6 Definition of the vessel boundary

1.6.1 Connections between the vessel and external piping:

a) for a welded connection, the groove end face of the first circumferential joint;

b) for a threaded connection, the end face of the first threaded joint;

c) for a flanged connection, the sealing face of the first flange;

d) for a connection made with a special connector or fitting, the first sealing face.

1.6.2 The pressure-retaining closures of nozzles, manholes and handholes, together with their flat covers and fasteners.

1.6.3 The connecting welds between non-pressure-retaining components and pressure-retaining components.

1.6.4 Non-pressure-retaining components attached directly to the vessel, such as supports and skirts.

1.6.5 The overpressure relief devices of the vessel.

1.7 For vessels or pressure-retaining components whose structural dimensions cannot be determined in accordance with this document, the following design methods may be used:

a) design by verification testing (such as experimental stress analysis or a proof hydrostatic test), in conformity with the provisions of GB/T 150.1;

b) comparative empirical design based on comparable structures that are already in service, in conformity with the provisions of GB/T 150.1;

c) design by stress analysis and assessment methods, including the finite element method, in conformity with the provisions of GB/T 150.1.

2 Normative references

The contents of the following documents constitute indispensable provisions of this document through normative references in the text. For dated references, only the edition corresponding to that date applies to this document. For undated references, the latest edition (including all amendments) applies to this document.

GB/T 150.1 Pressure vessels - Part 1: General requirements

GB/T 150.2 Pressure vessels - Part 2: Materials

GB/T 150.3 Pressure vessels - Part 3: Design

GB/T 150.4 Pressure vessels - Part 4: Fabrication, inspection and testing, and acceptance

GB/T 151 Heat exchangers

GB/T 196 General purpose metric screw threads - Basic dimensions

GB/T 197 General purpose metric screw threads - Tolerances

GB/T 1804 General tolerances - Tolerances for linear and angular dimensions without individual tolerance indications

GB/T 2965 Titanium and titanium alloy bars

GB/T 3620.1-2016 Designation and chemical composition of titanium and titanium alloys

GB/T 3620.2 Permitted deviations of chemical composition for titanium and titanium alloy processed products

GB/T 3621-2007 Titanium and titanium alloy sheets and plates

GB/T 3624-2010 Titanium and titanium alloy seamless tubes

GB/T 3625-2007 Titanium and titanium alloy tubes for heat exchangers and condensers

GB/T 4842 Argon

GB/T 4844 Pure helium, high purity helium and ultra-pure helium

GB/T 5193 Titanium and titanium alloy processed products - Method for ultrasonic inspection

GB/T 12337 Steel spherical tanks

GB/T 12969.1 Method for ultrasonic flaw detection of titanium and titanium alloy tubes

GB/T 12969.2 Method for eddy current flaw detection of titanium and titanium alloy tubes

GB/T 16598-2013 Titanium and titanium alloy discs and rings

GB/T 16749 Expansion joints of pressure vessels

GB/T 25198 Heads for pressure vessels

GB/T 31908 Tungsten electrodes for arc welding and plasma welding and cutting

HG/T 20592 to HG/T 20635 Steel pipe flanges, gaskets and fasteners

NB/T 11025 Reinforcing pads

NB/T 10558 Coating and transport packaging of pressure vessels

NB/T 47002.3 Clad plates for pressure vessels - Part 3: Titanium-steel clad plate

NB/T 47013.2 Non-destructive testing of pressure equipment - Part 2: Radiographic testing

NB/T 47013.3 Non-destructive testing of pressure equipment - Part 3: Ultrasonic testing

NB/T 47013.5 Non-destructive testing of pressure equipment - Part 5: Penetrant testing

NB/T 47013.7 Non-destructive testing of pressure equipment - Part 7: Visual testing

NB/T 47013.8 Non-destructive testing of pressure equipment - Part 8: Leak testing

NB/T 47014 Welding procedure qualification for pressure equipment

NB/T 47016 Mechanical property tests of product welded test coupons for pressure equipment

NB/T 47018.7 Technical specification for ordering welding consumables for pressure equipment - Part 7: Titanium and titanium alloy welding wire and filler wire

NB/T 47019.8 Technical specification for ordering tubes for boilers and heat exchangers - Part 8: Titanium and titanium alloys

NB/T 47020 to NB/T 47027 Flanges, gaskets and fasteners for pressure vessels

NB/T 47041 Tower vessels

NB/T 47042 Horizontal vessels

3 Terms and definitions

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

3.1 titanium pressure vessels - A pressure vessel whose shell is made entirely of titanium material.

3.2 inserted strip - A metal part placed underneath a strip cover or a lining. In most cases it is embedded in a machined groove in the shell of a clad plate vessel or of a lined vessel, so that it lies flush with the adjacent cladding layer or lining.

3.3 strip cover - A corrosion-resistant metal part laid over the cladding layer of a clad plate vessel or over the lining of a lined vessel and joined to it by fillet welding.

3.4 press working - A production method that makes use of the plastic deformation produced in a metal under the action of an external force in order to obtain raw material, blanks or finished products having a given shape, given dimensions and given mechanical properties.

4 General requirements

4.1 In addition to complying with the provisions of this document, the design, fabrication, inspection and acceptance of the vessel shall also comply with the requirements of the relevant laws, regulations, rules and safety technical codes promulgated by the State.

4.2 The design and fabrication of pressure vessels falling within the scope of TSG 21 shall be subject to the supervision of the special equipment safety supervision authorities.

4.3 The organizations that design and fabricate the vessel shall have a sound quality management system in effective operation.

4.4 Qualifications and responsibilities

4.4.1 Qualifications

a) For the design of pressure vessels falling within the scope of TSG 21, the design organization shall hold the corresponding special equipment (pressure vessel) design licence; the fabricator shall have obtained the corresponding special equipment (pressure vessel) design licence.

b) For the fabrication of pressure vessels falling within the scope of TSG 21, the fabricator shall hold the corresponding special equipment (pressure vessel) manufacturing licence.

4.4.2 Responsibilities

4.4.2.1 Responsibilities of the user or of the organization entrusting the design

The user of the vessel or the organization entrusting the design shall submit the design conditions of the vessel to the design organization in formal written form, and shall be responsible for the correctness and completeness of those design conditions. The design conditions of the vessel shall include at least the following:

a) the main standards and codes on which the design of the vessel is based;

b) the operating parameters (including working pressure, working temperature, liquid level height, nozzle loads and the like);

c) the place where the vessel is to be used and its natural conditions (including ambient temperature, seismic fortification intensity, wind load and snow load and the like);

d) the composition and characteristics of the medium;

e) the expected service life;

f) the geometric parameters and the orientation of the nozzles;

g) any other necessary conditions required for the design.

4.4.2.2 Responsibilities of the design organization

4.4.2.2.1 The design organization shall be responsible for the correctness and completeness of the design documents.

4.4.2.2.2 The design documents of the vessel shall include at least the strength calculation report or stress analysis report, the design drawings, the technical specification for fabrication and the risk assessment report (where required by the relevant regulations or by the party entrusting the design); where necessary, they shall also include instructions for installation, use and maintenance.

4.4.2.2.3 The general design drawing of a pressure vessel falling within the scope of TSG 21 shall bear the corresponding special equipment (pressure vessel) design seal.

4.4.2.2.4 The risk assessment report issued by the design organization shall comply with the provisions of GB/T 150.1.

4.4.2.2.5 The design organization shall retain the complete set of design documents of the vessel throughout its design service life.

4.4.2.3 Responsibilities of the fabricator

4.4.2.3.1 The fabricator shall carry out fabrication in accordance with the requirements of the design documents. Where it is necessary to modify the original design, the written agreement of the original design organization to the modification shall be obtained, and a detailed record shall be made of the modified part.

4.4.2.3.2 Before fabrication of the vessel begins, the fabricator shall draw up a comprehensive quality plan, the content of which shall include at least the fabrication process control points, the inspection items and the acceptance criteria for the vessel or for its pressure-retaining components.

4.4.2.3.3 The inspection department of the fabricator shall, during fabrication of the vessel and after its completion, carry out on the vessel the various inspections and tests specified in this document, in the design drawings and in the quality plan, shall issue the corresponding reports and shall be responsible for the correctness and completeness of those reports.

4.4.2.3.4 After the vessel has passed inspection, the fabricator shall issue a product quality certificate.

4.4.2.3.5 For each vessel it fabricates, the fabricator shall retain the following technical documents for inspection for at least the design service life of the vessel:

a) the quality plan;

b) the fabrication process drawings or process cards;

c) the product quality certification documents;

d) the welding procedure and heat treatment procedure documents of the vessel;

e) the records of the inspections and tests selected by the fabricator among those permitted by the standard;

f) the records of the checks, inspections and tests carried out during fabrication and after completion of the vessel;

g) the original design drawing and the as-built drawing of the vessel.

4.5 General provisions for design

4.5.1 The design organization (design personnel) of the vessel shall design strictly in accordance with the design conditions of the vessel supplied by the user or by the organization entrusting the design, shall consider all failure modes that may arise during service of the vessel and shall propose measures to prevent failure. The calculation of the strength, stiffness and stability of the pressure-retaining components of the vessel shall comply with GB/T 150.3 and with the relevant provisions of this document.

4.5.2 Loads - The following loads shall be considered in the design:

a) internal pressure, external pressure or maximum pressure difference;

b) the static head of liquid; where the static head of liquid is less than 5% of the design pressure it may be neglected;

The following loads shall also be considered where necessary:

c) the dead weight of the vessel (including internals and packing) together with the gravity load of the medium contained in it under normal working conditions or in the condition of the pressure test;

d) the gravity loads of attached equipment and of insulating material, lining, piping, ladders and platforms;

e) wind load, seismic load and snow load;

f) the reactions of supports, saddle rings, lifting lugs and other types of support members;

g) the actions exerted by connected piping and by other components;

h) the actions caused by temperature gradients or by differential thermal expansion;

i) impact loads, including impact loads caused by rapid pressure fluctuations and reaction forces caused by fluid impact;

j) the actions arising during transport or lifting.

4.5.3 In determining the design pressure or the calculation pressure, the following shall be considered:

a) where the vessel is fitted with an overpressure relief device, the design pressure shall be determined in accordance with the provisions of GB/T 150.1;

b) in determining the design pressure of a vessel subject to external pressure, consideration shall be given to the maximum internal to external pressure difference that may occur under normal working conditions;

c) in determining the shell thickness of a vacuum vessel, the design pressure shall be taken as for a vessel subject to external pressure. Where a safety control device (such as a vacuum relief valve) is fitted, the design pressure shall be taken as the lower of 1.25 times the maximum internal to external pressure difference and 0.1 MPa; where no safety control device is fitted, it shall be taken as 0.1 MPa;

d) for a vessel made up of two or more pressure chambers, such as a jacketed vessel, the design pressure of each chamber shall be determined separately; in determining the calculation pressure of a component common to two chambers, the maximum pressure difference between the adjacent chambers shall be considered.

4.5.4 In determining the design temperature, the following shall be considered:

a) the design temperature shall not be lower than the highest temperature that the metal of the component may reach under working conditions. For metal temperatures below 0 degrees Celsius, the design temperature shall not be higher than the lowest temperature that the metal of the component may reach;

b) where the metal temperature of the various parts of the vessel under working conditions is different, a design temperature may be set separately for each part;

c) the metal temperature of a component may be obtained by heat transfer calculation, or measured on a vessel already in service under the same operating conditions, or determined on the basis of the temperature of the medium inside the vessel combined with the external conditions;

d) in determining the minimum design metal temperature, full account shall be taken of the influence of low atmospheric ambient temperature conditions on the metal temperature of the vessel shell during operation. The low atmospheric ambient temperature condition is the lowest value of the mean of the monthly minimum air temperatures over the years (that is, the sum of the lowest daily air temperatures in the month divided by the number of days in that month).

4.5.5 A vessel that operates under several different operating conditions shall be designed for the most severe condition; where necessary, combinations of different operating conditions shall also be considered, and the pressure and temperature values corresponding to each operating condition and each design condition shall be indicated on the drawing or in the corresponding technical documents.

4.5.6 Thickness addition - The thickness addition shall be determined by formula (1), C equals C1 plus C2, where C is the thickness addition, in millimetres; C1 is the value of the negative deviation on the thickness of the titanium material, determined in accordance with 4.5.6.1, in millimetres; C2 is the value of the corrosion allowance, determined in accordance with 4.5.6.2, in millimetres.

4.5.6.1 Negative deviation on the thickness of titanium material - The negative deviation on the thickness of titanium plate or titanium tube shall be as specified in the relevant titanium material standard.

4.5.6.2 Corrosion allowance - In order to prevent a reduction of thickness of the components of the vessel through corrosion or mechanical wear, a corrosion allowance shall be considered; the detailed provisions are as follows:

a) for components subject to corrosion or wear, the corrosion allowance shall be determined on the basis of the expected design service life of the vessel and of the corrosion rate (or wear rate) of the medium on the metallic material;

b) where the degree of corrosion to which the various components of the vessel are subjected is different, different corrosion allowances may be adopted.

4.5.7 The minimum thickness of the shell after machining and forming, not including the corrosion allowance, is 2 mm.

4.5.8 The nominal thickness and the minimum forming thickness of the pressure-retaining components of the vessel shall as a rule be indicated on the design drawing.

4.5.9 Type A and type B welded joints of the vessel shell shall be of the butt joint type with full penetration over the entire cross section.

4.5.10 For the expanded joints between titanium heat exchanger tubes and steel (in particular austenitic stainless steel) tubesheets, the influence of a rise in temperature on the strength of the expanded joint shall be considered.

4.6 Allowable stress

4.6.1 The allowable stress of titanium material shall be selected in accordance with Clause 5. The basis for determining the allowable stress of titanium material shall be as specified in Table 1.

Table 1 gives the basis for determining the allowable stress in MPa as the minimum of the following values: the standard tensile strength at room temperature divided by 2.7; the tensile strength at design temperature divided by 2.7; the specified non-proportional extension strength at room temperature divided by 1.5; the specified non-proportional extension strength at design temperature divided by 1.5; the average value of the stress causing rupture after 100 000 hours at design temperature divided by 1.5; and the stress producing a creep rate of 1% after 100 000 hours at design temperature divided by 1.0.

In Table 1, Rm is the lower limit value of the standard tensile strength of the titanium material at room temperature, in megapascals (MPa); the tensile strength at design temperature is the value of the tensile strength of the titanium material at the design temperature, in megapascals (MPa); Rp0.2 is the value of the standard specified non-proportional extension strength of the titanium material at room temperature, in megapascals (MPa); the corresponding value at design temperature is the value of the specified non-proportional extension strength of the titanium material at the design temperature, in megapascals (MPa); RD is the average value of the stress causing rupture of the titanium material after 100 000 hours at the design temperature, in megapascals (MPa); Rn is the value of the creep limit corresponding to a creep rate of 1% after 100 000 hours at the design temperature, in megapascals (MPa).

4.6.2 Where the design temperature is lower than 20 degrees Celsius, the allowable stress at 20 degrees Celsius shall be taken.

4.6.3 Allowable axial compressive stress - The allowable axial compressive stress of a cylinder or of a tube shall be taken as the lower of the allowable stress value of the material at the design temperature (see Clause 5) and the value obtained by the method specified in items a) and b) of this subclause. The coefficient B shall be obtained by the following steps:

a) on the basis of the outside radius and of the effective thickness of the cylinder or tube, the coefficient A shall be calculated by formula (2), A equals 0.094 times the effective thickness divided by the outside radius, where A is the external pressure strain coefficient, the effective thickness of the cylinder or tube is expressed in millimetres (mm) and the outside radius of the cylinder or tube is expressed in millimetres (mm);

b) using the external pressure stress coefficient curve chart corresponding to the material of the cylinder (Figure 1 to Figure 8), the value of B shall be obtained from the temperature line. Within the elastic range (the straight portion of the chart or the region to its left), B may be calculated by formula (3), B equals two thirds of the product of A and E, where B is the value of the external pressure stress coefficient, in megapascals (MPa); E is the value of the modulus of elasticity of the material at the design temperature, in megapascals (MPa); and A is the external pressure strain coefficient.

4.7 Classification of welded joints and welded joint coefficient

4.7.1 The welded joints of the vessel shall be classified in accordance with the provisions of GB/T 150.1.

4.7.2 The welded joint coefficient shall be determined on the basis of the type of welded joint of the pressure-retaining component and of the length proportion of radiographic or ultrasonic testing carried out:

a) double-welded butt joints and butt joints with full penetration equivalent to double-welded butt joints, with 100% radiographic or ultrasonic testing: joint coefficient equal to 1.0;

b) single-welded butt joints (with a backing strip closely fitted to the base metal along the whole length of the weld root): with 100% radiographic or ultrasonic testing, joint coefficient equal to 0.9; with local radiographic or ultrasonic testing, joint coefficient equal to 0.8; where radiographic or ultrasonic testing cannot be carried out, joint coefficient equal to 0.65;

c) single-welded circumferential butt joints without backing strip, where radiographic or ultrasonic testing cannot be carried out: joint coefficient equal to 0.6.

Note: where conditions permit, 100% radiographic or ultrasonic testing should preferably be selected for type A and type B welded joints of titanium pressure vessels.

4.8 Pressure test

4.8.1 General requirements

4.8.1.1 The pressure test includes the hydrostatic test, the pneumatic test and the combined gas and liquid pressure test.

4.8.1.2 After fabrication of the vessel has been completed, a pressure test shall be carried out; the type of test, the requirements and the value of the test pressure shall be indicated on the drawing.

4.8.1.3 The pressure test is normally the hydrostatic test. For vessels for which the hydrostatic test is not suitable, the pneumatic test or the combined gas and liquid pressure test may be adopted.

4.8.1.4 Where the combined gas and liquid pressure test is adopted, the test pressure shall be as specified for the pneumatic test.

4.8.1.5 Where a vessel subject to external pressure is pressure tested with internal pressure, the test pressure shall be as specified in 4.8.2.3.

4.8.1.6 For a multi-chamber vessel made up of two or more pressure chambers, the test pressure of each chamber shall be determined on the basis of its own design pressure, and each chamber shall be pressure tested separately:

a) the stability of the components common to two chambers under the test pressure shall be checked;

b) where the stability requirement cannot be satisfied, a leak check shall first be carried out and, once it has been passed, the pressure test shall be performed. During the pressure test a certain pressure shall be maintained inside the adjacent chamber, so that at any moment of the whole test process (including pressurization, holding and depressurization) the pressure difference between the chambers does not exceed the allowable pressure difference; this requirement and the value of the allowable pressure difference shall be indicated on the drawing;

c) where it is necessary to increase the test pressure of a given chamber, the provisions of 4.8.3 shall be complied with.

4.8.2 Pressure test pressure

4.8.2.1 The minimum value of the pressure test pressure shall be as specified in 4.8.2.2 and 4.8.2.3, and the following shall also be considered:

a) where a vertical vessel is hydrostatically tested in the horizontal position, the test pressure shall include the static head of liquid corresponding to the vertical test position;

b) where the static head of the medium contained in the vessel under working conditions is greater than the static head of liquid of the hydrostatic test, the test pressure shall be increased accordingly, as appropriate.

4.8.2.2 Vessels subject to internal pressure - For the hydrostatic test the test pressure shall be calculated by formula (4), the test pressure being equal to 1.25 times the design pressure multiplied by the ratio of the allowable stress at the test temperature to the allowable stress at the design temperature. For the pneumatic test or the combined gas and liquid pressure test the test pressure shall be calculated by formula (5), the test pressure being equal to 1.1 times the design pressure multiplied by the same ratio of allowable stresses.

In formulae (4) and (5), the test pressure is the pressure of the test; the design pressure is the design pressure of the vessel; the allowable stress at the test temperature is the allowable stress of the material of the vessel component at the test temperature; and the allowable stress at the design temperature is the allowable stress of the material of the vessel component at the design temperature.

Note 1: where the maximum allowable working pressure is specified in the design documents, the maximum allowable working pressure shall be used in the formulae in place of the design pressure.

Note 2: where the materials or the design temperatures of the main pressure-retaining components of the vessel (such as the shell, the heads, the nozzles, the flanges and the fasteners) are different, the smallest of the ratios of the allowable stress at the test temperature to the allowable stress at the design temperature of the materials of those components shall be taken.

4.8.2.3 Vessels subject to external pressure - For the hydrostatic test the test pressure shall be calculated by formula (6), the test pressure being equal to 1.25 times the design pressure. For the pneumatic test or the combined gas and liquid pressure test the test pressure shall be calculated by formula (7), the test pressure being equal to 1.1 times the design pressure. In these formulae the test pressure is the pressure of the test and the design pressure is the design pressure of the vessel.

4.8.3 Stress check for the pressure test - Where a test pressure higher than that specified in 4.8.2.2 and 4.8.2.3 is adopted, the stress level of each pressure-retaining component under the test conditions shall be checked before the pressure test; for example, for the shell components the maximum total membrane stress under the test conditions shall be checked as follows: a) for the hydrostatic test, the membrane stress shall not exceed 0.9 times the specified non-proportional extension strength multiplied by the welded joint coefficient; b) for the pneumatic test or the combined gas and liquid pressure test, the membrane stress shall not exceed 0.8 times the specified non-proportional extension strength multiplied by the welded joint coefficient. In these expressions the specified non-proportional extension strength is the value of the 0.2% non-proportional extension strength of the shell material at the test temperature, in megapascals (MPa), and the welded joint coefficient is that of the cylinder.

4.8.4 For vessels on which the pressure test cannot be carried out in accordance with the above provisions, the design organization shall propose the safety measures to be adopted in order to dispense with the pressure test while ensuring the safe operation of the vessel; these measures shall be approved by the person technically responsible in the design organization and shall be indicated on the drawing.

4.9 Leak test

4.9.1 The leak test includes the gas tightness test, the ammonia leak test, the helium leak test and similar tests.

4.9.2 Vessels containing a medium whose degree of toxicity is extreme or high, or vessels in which even a minute leak is not permitted, shall be subjected to the leak test after the pressure test has been passed.

Note: the degree of toxicity of the medium shall be determined in accordance with the relevant provisions of TSG 21.

4.9.3 The design organization shall specify the method and the technical requirements of the leak test of the vessel.

4.9.4 Where a leak test has to be carried out, the test pressure, the test medium and the corresponding inspection requirements shall be indicated on the drawing and in the design documents.

4.9.5 The test pressure of the gas tightness test is the design pressure.

5 Materials

5.1 General requirements

5.1.1 The titanium materials used in titanium pressure vessels shall comply with the provisions of this document; the non-titanium materials used shall comply with the requirements of the corresponding pressure vessel product standards for those materials.

5.1.2 The chemical composition, mechanical properties, corrosion resistance, technological properties and physical properties of the titanium materials used in the vessel shall satisfy the requirements of fabrication and service.

5.1.3 The designations of the titanium materials used in the vessel are TA0, TA1, TA1G, TA2, TA2G, TA3, TA3G, TA8, TA8-1, TA9, TA9-1 and TA10. Their chemical compositions shall comply with the provisions of GB/T 3620.1 respectively; the sampling and analysis methods for the chemical analysis of finished pressure-worked titanium products, and the permitted deviations of the chemical composition, shall comply with the provisions of GB/T 3620.2.

5.1.4 Where a titanium material corresponds to the material type, designation and condition listed in this document but its dimensions exceed the range listed, it may be selected provided that it also satisfies the following requirements: a) the elongation after fracture of TA3 and TA10 (class A) is not less than 15% and the elongation after fracture of titanium materials of the other designations is not less than 18%; b) the mechanical properties other than the elongation after fracture comply with the provisions of this document.

5.1.5 The titanium material used in the vessel shall be in the annealed condition.

5.1.6 Where the design temperature of the vessel is not higher than minus 60 degrees Celsius, the elongation after fracture of the titanium material at a temperature not higher than the design temperature shall be verified; the elongation after fracture of TA3 and TA10 (class A) shall not be less than 15% and the elongation after fracture of titanium materials of the other designations shall not be less than 18%.

5.1.7 Where titanium materials not listed in this document, or titanium materials of foreign designations, are selected, the provisions of TSG 21 shall be complied with.

5.2 Titanium plate

5.2.1 The TA1G, TA2G, TA3G, TA8, TA8-1, TA9, TA9-1 and TA10 titanium plates used in the vessel shall comply respectively with the provisions of GB/T 3621 for TA1, TA2, TA3, TA8, TA8-1, TA9, TA9-1 and TA10 plate; the room temperature mechanical properties of the TA0, TA1, TA2 and TA3 titanium plates used in the vessel shall comply with the provisions of Table 2, and the other requirements shall comply with the provisions of GB/T 3621.

Table 2 gives the room temperature mechanical properties of TA0, TA1, TA2 and TA3 titanium plate. TA0, annealed, thickness 0.3 mm to 25.0 mm: tensile strength 280 MPa, specified non-proportional extension strength 170 MPa, elongation after fracture 30%; bend test: for a thickness in the range from 0.3 mm to 5.0 mm inclusive, bend former diameter three times the thickness, bend angle 140 degrees.

Table 2, TA1, annealed, thickness 0.3 mm to 25.0 mm: tensile strength 370 MPa, specified non-proportional extension strength 250 MPa, elongation after fracture 30%; bend test: for a thickness in the range from 0.3 mm to 2.0 mm inclusive, bend former diameter three times the thickness, bend angle 140 degrees; for a thickness greater than 2.0 mm and up to 5.0 mm inclusive, bend former diameter three times the thickness, bend angle 130 degrees.

Table 2, TA2, annealed, thickness 0.3 mm to 25.0 mm: tensile strength 440 MPa, specified non-proportional extension strength 320 MPa, elongation after fracture 25%; bend test: for a thickness in the range from 0.3 mm to 2.0 mm inclusive, bend former diameter three times the thickness, bend angle 100 degrees; for a thickness greater than 2.0 mm and up to 5.0 mm inclusive, bend former diameter three times the thickness, bend angle 90 degrees.

Table 2, TA3, annealed, thickness 0.3 mm to 25.0 mm: tensile strength 540 MPa, specified non-proportional extension strength 410 MPa, elongation after fracture 20%; bend test: for a thickness in the range from 0.3 mm to 2.0 mm inclusive, bend former diameter three times the thickness, bend angle 90 degrees; for a thickness greater than 2.0 mm and up to 5.0 mm inclusive, bend former diameter three times the thickness, bend angle 80 degrees.

5.2.2 Where titanium plate of thickness greater than 20 mm is selected for the fabrication of pressure-retaining components, each plate shall be subjected to ultrasonic testing in accordance with the provisions of GB/T 5193 and shall satisfy the requirements of class A.

5.2.3 For titanium plate on which corrosion resistance tests have to be carried out, the test method and the acceptance criteria shall be stated when the material is ordered.

5.2.4 The allowable stresses of titanium plate shall be selected from Table 7.

5.3 Titanium tube

5.3.1 The TA1G, TA2G, TA3G, TA8, TA8-1, TA9, TA9-1 and TA10 non-heat-exchanger titanium tubes used in the vessel shall comply with the provisions of GB/T 3624 for TA1, TA2, TA3, TA8, TA8-1, TA9, TA9-1 and TA10 tube; the room temperature mechanical properties of the TA0, TA1 and TA2 non-heat-exchanger titanium tubes used in the vessel shall comply with the provisions of Table 3, and the other requirements shall comply with the provisions of GB/T 3624.

5.3.2 The TA1G, TA2G, TA3G, TA9 and TA10 heat exchanger titanium tubes used in heat exchangers shall comply with the provisions of NB/T 47019.8; the room temperature mechanical properties of the TA9-1 heat exchanger titanium tubes used in heat exchangers shall comply with the provisions of GB/T 3625 and the other requirements shall comply with the provisions of NB/T 47019.8; the chemical composition of the TA0, TA1 and TA2 heat exchanger titanium tubes used in heat exchangers shall comply with the provisions of GB/T 3620.1, their room temperature mechanical properties shall comply with the provisions of Table 3 and their other requirements shall comply with the provisions of NB/T 47019.8.

Table 3 gives the room temperature mechanical properties of TA0, TA1 and TA2 titanium tube. TA0, annealed: tensile strength 280 MPa, specified non-proportional extension strength 170 MPa, elongation after fracture 24%. TA1, annealed: tensile strength 370 MPa, specified non-proportional extension strength 250 MPa, elongation after fracture 20%. TA2, annealed: tensile strength 440 MPa, specified non-proportional extension strength 320 MPa, elongation after fracture 18%.

5.3.3 Where titanium tube conforming to GB/T 3624 is selected for the fabrication of pressure-retaining components, each length of titanium tube shall be subjected to a hydrostatic (pneumatic) test; where the design pressure exceeds 10 MPa, the titanium tube shall also be subjected to ultrasonic or eddy current testing in accordance with the provisions of GB/T 12969.1 or GB/T 12969.2.

5.3.4 For titanium tube on which corrosion resistance tests have to be carried out, the test method and the acceptance criteria shall be stated when the material is ordered.

5.3.5 The allowable stresses of titanium tube shall be selected from Table 8.

5.4 Titanium forgings

5.4.1 The TA1G, TA2G, TA3G, TA9 and TA10 titanium forgings shall correspond respectively to and comply with the provisions of GB/T 16598 for TA1, TA2, TA3, TA9 and TA10 forgings; the room temperature mechanical properties of the TA0, TA1, TA2 and TA3 titanium forgings shall comply with the provisions of Table 4 and their other requirements shall comply with the provisions of GB/T 16598.

Table 4 gives the room temperature mechanical properties of TA0, TA1, TA2 and TA3 titanium forgings, for a cross-sectional area not greater than 100 square centimetres and in the annealed condition. TA0: tensile strength 280 MPa, specified non-proportional extension strength 170 MPa, elongation after fracture 30%, reduction of area 35%. TA1: tensile strength 370 MPa, specified non-proportional extension strength 250 MPa, elongation after fracture 30%, reduction of area 35%. TA2: tensile strength 440 MPa, specified non-proportional extension strength 320 MPa, elongation after fracture 20%, reduction of area 35%. TA3: tensile strength 540 MPa, specified non-proportional extension strength 410 MPa, elongation after fracture 20%, reduction of area 30%.

5.4.2 Titanium forgings used to fabricate pressure-retaining components shall be subjected, piece by piece, to 100% surface testing in accordance with NB/T 47013.5, with acceptance at level I; whether ultrasonic testing is to be carried out shall be determined by the design organization on the basis of the service requirements.

5.4.3 For titanium forgings on which corrosion resistance tests have to be carried out, the test method and the acceptance criteria shall be stated when the material is ordered.

5.4.4 The allowable stresses of titanium forgings shall be selected from Table 9.

5.5 Titanium bar

5.5.1 TA1G, TA2G, TA3G, TA9 and TA10 titanium bars shall correspond respectively to and comply with the provisions of GB/T 2965 for TA1, TA2, TA3, TA9 and TA10 bar; the chemical composition of TA0, TA1, TA2 and TA3 titanium bars shall comply with the provisions of GB/T 3620.1, their room temperature mechanical properties shall comply with the provisions of Table 5 and their other requirements shall comply with the provisions of GB/T 2965.