1、BRITISH STANDARD BS 6990:1989 Including Amendment No. 1 not issued separately Code of practice for Welding on steel pipes containing process fluids or their residuals ICS 25.160.10BS6990:1989 This British Standard, having been prepared under the directionof the Welding Standards Committee, was publi
2、shed under the authority ofthe Board of BSI and comes intoeffect on 28February 1989 BSI 04-1999 First published as DD 39, July1974 First published as BS6990, February 1989 The following BSI references relate to the work on this standard: Committee reference WEE/21 Draft for comment 86/78728 DC ISBN
3、0 580 16672 4 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Welding Standards Committee (WEE/-) to Technical Committee WEE/21, upon which the following bodies were represented: Associated Offices Technical Committee British Gas plc Bri
4、tish Non-Ferrous Metals Federation British Steel Industry Electricity Supply Industry in England and Wales Engineering Equipment and Materials Users Association Health and Safety Executive Heating and Ventilating Contractors Association Institute of Refrigeration Institution of Gas Engineers Institu
5、tion of Mechanical Engineers Joint Industry Board for Plumbing Mechanical Engineering Services in England and Wales National Association of Plumbing, Heating and Mechanical Services Contractors Power Generation Association (BEAMA Ltd.) Stainless Steel Fabricators Association of Great Britain Tubes I
6、nvestments Limited United Kingdom Atomic Energy Authority Water Tube Boilermakers Association Welding Institute Welding Manufacturers Association (BEAMA Ltd.) The following bodies were also represented in the drafting of the standard, through subcommittees and panels: Association of Consulting Engin
7、eers British Institute of Non-destructive Testing Department of Energy (Petroleum Engineering Division) Institution of Production Engineers Pipeline Industries Guild United Kingdom Offshore Operators Association Water Research Centre Amendments issued since publication Amd. No. Date of issue Comment
8、s 9772 February 1998 Indicated by a sideline in the marginBS6990:1989 BSI 04-1999 i Contents Page Committees responsible Inside front cover Foreword ii Section 1. General 1 Scope 1 2 Definitions 1 3 Information, items to be approved and items to be agreed and to be documented 2 Section 2. Safety con
9、siderations 4 Legal requirements 4 5 Preliminary considerations 4 6 Factors affecting safety 4 Section 3. Welding 7 Pipe thickness, temperature and internal pressure 6 8 Pipe material 6 9 Fitting material 6 10 Welding equipment 6 11 Electrodes and filler metals 6 12 Shielding gases 7 13 Approval and
10、 testing of welding procedures 7 14 Approval and testing of welders 12 15 Preparation of pipe 12 16 Inspection of fittings 13 17 Fusion faces 13 18 Preparation for encirclement fitting 13 19 Preparation for set-on fitting 16 20 Alignment of flanged fittings 16 21 Working clearance 17 22 Stray arcs 1
11、7 23 Weather conditions 17 24 Preheating 17 25 Sequence of welding 17 26 Inter-run cleaning 18 27 Inspection 18 28 Non-destructive testing acceptance criteria 19 29 Rectification of welds 19 Figure 1 Typical fittings 3 Figure 2 Typical longitudinal weld preparation for fitting: dimensions and tolera
12、nces 14 Figure 3 Attachment of run-on/run-off plates to backing material 15 Figure 4 Typical yoke-type clamp for encirclement tee fittings 16 Table 1 Welding procedure details 10 Table 2 Changes affecting procedure approval (essential variables) 11 Publications referred to Inside back coverBS6990:19
13、89 ii BSI 04-1999 Foreword This British Standard Code of Practice has been prepared under the direction of the Welding Standards Committee. It is based on an up-dating of Draft for Development DD39 which is withdrawn. It reflects the latest knowledge in the welding on steel pipelines and pipework wh
14、ich contain or have contained process fluids or the residuals of such process fluids, and covers welding operations where attachments are required and where it is not necessary or practical to decommission and/or decontaminate the system. This method of attachment is sometimes, but incorrectly, term
15、ed “hot tapping”. Reference to current legislation is essential before any attempt to undertake work of this nature, and to follow the details of this code. Since the preparation of DD39 in 1974 considerable experience has been gained as the result of both on-shore and off-shore North Sea developmen
16、ts. To this knowledge has been added the expertise gained in the process plant field, resulting in an unified code which covers both spheres. Although new developments and refinements can be expected to emerge in the future, particularly with regard to off-shore exploration, the methods and recommen
17、dations in this code are considered to reflect up to date knowledge and sufficient experience of practical use to merit their adoption. The up-dating has been extensive, covering practically every aspect of the technical changes in materials, welding technology and non-destructive testing. The main
18、purpose of this code is to give general details for welding, testing and acceptance criteria. Since the design, choice of materials and methods of construction are not covered by this code, reference should be made to the appropriate standards, such as CP2010-2, BS4515, BS2633, BS4677 and BS8010-1.
19、To ensure that the workmanship and welding follow the details of this code, it would be normal for the contractor as well as the organization undertaking this specialist work to have and employ a suitable quality control system such as is recommended in BSENISO9000. Because of the wide range of pipe
20、lines and pipework and the products that can be conveyed and the range of attachments that may be required, general guidance has been given on some aspects. Specific details will be for agreement between the contracting parties after due consideration of the prevailing service conditions. The techni
21、ques and equipment described herein require extensive facilities and specialist personnel and as such should not be attempted without such specialist equipment and personnel. The use of the words “imperfection” or “flaw” or other phrases containing the words “imperfection” or “flaw” in this code is
22、not intended to imply a defective condition or any lack of integrity of the weld as it is known that all welds contain certain features described as artefacts, flaws, imperfections or discontinuities. The acceptance criteria have been based on the present technical analysis of the various types, siz
23、es, shapes and positions of these anomalies and on the suitability of the whole weld for its specific service. Pipe dimensions. Unless otherwise qualified, for the purposes of this code nominal values of outside diameter and thickness of pipe apply. It has been assumed in the drafting of this code t
24、hat the execution of its provisions is entrusted to appropriately qualified and experienced people.BS6990:1989 BSI 04-1999 iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Complian
25、ce with a British Standard does not of itself confer immunity from legal obligations. (See clause 4). Summary of pages This document comprises a front cover, an inside front cover, pagesi to iv, pages1 to20, an inside back cover and a back cover. This standard has been updated (see copyright date) a
26、nd may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankBS6990:1989 BSI 04-1999 1 Section 1. General 1 Scope This code covers operations relating to and involving arc welding on ferritic steel and austenitic stainless steel land or off
27、shore pipelines and process plant pipework which contain or have contained a process fluid and which are at least 5mm thick. It gives details of procedures prior to, during and after all these operations. NOTE 1Welding on pipes of thickness below 5mm is not covered by this code although it can be un
28、dertaken. The code covers manual, semi-automatic and mechanized arc welding by the following processes or combination of processes: a) manual metal-arc welding; b) MIG/MAG welding; c) TIG welding; d) flux cored arc welding; e) non-shielded welding. It is essential that the items listed in clause 3 s
29、hould be fully documented and followed. Welding operations needing post-weld heat treatment for adequate weld quality are not within the scope of this code. This code is not applicable to a pipeline or pipework that has been fully isolated and decontaminated or has not been commissioned. These are c
30、overed by other standards such as BS2633, BS4677 and BS4515. This code does not relate to a pipeline or pipework containing a process fluid or its residuals that will become explosively unstable upon the application of heat or will affect the pipe material by rendering it susceptible to ignition, st
31、ress corrosion cracking or embrittlement. NOTE 2The titles of the publications referred to in this code are listed on the inside back cover. 2 Definitions For the purposes of this code the definitions given in BS 499-1 apply together with the following. NOTETerms marked with an asterisk (*) are take
32、n from BS499-1. 2.1 employer the owner of the pipeline or pipework NOTEThe employer may act through a consultant, an inspector or other authorized representative. 2.2 contractor the firm undertaking the contract and any subcontractors engaged in work covered by this code 2.3 inspector the body, asso
33、ciation or employee that ensures that the materials and construction are in accordance with this code 2.4 statutory authority the body or organization that, through the power vested in it by Government Statute, regulates the requirements with which particular pipelines or pipework have to comply NOT
34、EOne way in which such requirements may be promulgated is by making reference to British Standards. 2.5 joint the completed weld joining two sections of pipe, a section of pipe to a fitting or two fittings 2.6 welding procedure* a specific course of action followed in welding, including a list of ma
35、terials and, where necessary, tools to be used 2.7 welding procedure test the making and testing of a welded joint, representative of that to be used on an actual job, in order to prove the feasibility of a welding procedure NOTEThis term is not usually applied to any tests that may have been made d
36、uring the development of a welding procedure. 2.8 approved welding procedure a documented welding procedure that has been approved by an inspecting authority either by means of a welding procedure test or as a result of authentic documented experience gained with the welding of joints similar to tha
37、t to which the welding procedure applies 2.9 welder* the operator who performs the welding 2.10 approved welder a welder who has demonstrated his ability to produce welds meeting the details of this code 2.11 root run* the first run deposited in the root of a multi-run weld NOTEAlso known as a “stri
38、nger bead” in vertical-down welding.BS6990:1989 2 BSI 04-1999 2.12 positional welding welding wherein the pipe or assembly is held stationary 2.13 semi-automatic welding* welding in which some of the welding variables are automatically controlled, but manual guidance is necessary 2.14 mechanized wel
39、ding* welding in which the welding parameters are controlled mechanically or electronically and may be manually varied during welding to maintain the required welding conditions 3 Information, items to be approved and items to be agreed and to be documented 3.1 Information to be supplied by the empl
40、oyer The following information to be supplied by the employer should be fully documented and followed. a) The location and identification of the pipeline or pipework. b) The type of process fluid and its temperature, pressure and flow rate. (See also 5.3 and 5.8.) c) The composition of the pipe mate
41、rial if known. d) The type of fitting to be used and its position on the pipe. NOTETypical fittings are shown in Figure 1. e) Whether batch testing of electrodes and filler metals is required (see 11.1). f) The interval before testing the test welds if other than 24 h see 13.2 4)ii). g) The period f
42、or which records of approved welding procedures should be kept (see 13.3). h) Whether prevailing weather conditions are such that welding is not to be carried out (seeclause 23). NOTEThis information may not be able to be supplied until the appropriate stage of the work is reached. i) The methods of
43、 non-destructive testing (see27.1, 27.3, 27.4 and 27.5) and the Examination Level to be used when ultrasonic examination in accordance with BS 3923-1 is to be applied (see 27.5). NOTEThe agreement of the statutory authority may also be required. 3.2 Items to be approved by the employer The following
44、 items to be approved by the employer should be fully documented and followed. a) The minimum tensile strength of weld metal for fillet welds when this need not be as high as the minimum specified for the parent metal see11.1 b). NOTEThe agreement of the statutory authority may also be required. b)
45、Electrodes and filler metals to be used (see11.1). c) Documentation relating to welding procedure approval (see 13.3). d) Use of diameter and thickness grouping for welding procedure approval see 13.4 b). e) Use of a plate butt joint to simulate a longitudinal butt weld for welding procedure approva
46、l see 13.4 c). f) The welding procedure used for repairing defects in an encirclement fitting (see 18.1). g) The thermal cutting method for making large modifications to the radius of a set-on fitting (see19.1). h) Repair or rejection of arc strikes (seeclause22). i) Non-destructive testing procedur
47、es (see 27.1). j) Inspection personnel (see 27.1). 3.3 Items to be agreed The following items to be agreed between the contracting parties should be fully documented and followed. a) The minimum pipe thickness on which welding is to be carried out when the conditions are other than those detailed in
48、 clause 7 (see clause 7). b) The specification of the material for a fitting (see clause 9). c) The definition of a batch when batch testing of electrodes and filler metals is required (see 11.1).BS6990:1989 BSI 04-1999 3 Figure 1 Typical fittingsBS6990:1989 4 BSI 04-1999 Section 2. Safety considera
49、tions 4 Legal requirements All persons involved in welding operations on steel pipes have a duty to make themselves aware of all current legislation relative to their industry. 5 Preliminary considerations 5.1 The application of heat to a pipe containing a process fluid or a residue during preheating or welding operations can be, potentially, very hazardous. Flammable substances may explode, toxic materials may escape and some chemicals when heated may react with the metal of the pipe itself. For these reasons all such operations should always be care
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