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Module 5 Module 5 Document Transcript

  • MODULE – 5 DOCUMENTS GOVERNING WELDING INSPECTION AND QUALIFICATION Tolerance is total amount of variations permitted from design size. Tolerance may be expressed as below—1. As a variation between limits. 2. As the design size 3. When only one value is given, the other value is assumed zero. Large tolerances reduce the manufacturing cost. Hold points – These are pre arranged steps in fabrication process to permit interim inspection. CWI has to review 3 basic types of documents. CODES, STANDARDS, AND SPECIFICATIONS. 96/ 184-- CODES—It is a body laws arranged systematically for easy reference. Codes consists of laws having legal status, hence it is mandatory. Welding inspector will inspect work according to some code. Welding inspector who inspects according to any code may be required to refer several sections of code. STANDARDS -- Some thing established for use as a rule or basis of comparison in measuring or judging capacity, quantity, content, quality etc. The term standard also applies to numerous types of documents including codes and specifications. Some other documents which are considered as standards are procedures, recommended practice, classification and definitions of terms. Some standards are considered as mandatory. Mandatory standards are precise, clearly defined and suitable for adoption as apart of a law or regulations. Codes are examples of mandatory standards as they have legal status. A recommended practice is a non mandatory standard. The implication of non mandatory is that these serve as a guide lines for the performance of a particular task, non mandatory standard use should and could in place of shall and will. It however does not mean that some thing is rejectable just because it fails to comply with guide lines. Most American standards are developed as per rules framed by ANSI. 97/184- ANSI, ASME, ASTM Standards are reviewed by ANSI. API-1104 This standard applies to cross country pipe lines. This standard covers requirement for welder qualification, welding procedure qualification. It applies to gas and arc welding of butt and T joints in pipes used in compression, pumping and transmission of crude petroleum, petro products, and fuel gasses. API 1104 includes requirement for visual and radiographic inspection of these welds. 98/184—SPECIFICATIONS – It is a detailed description or listing of required attributes of some items or operations. AWS A 5.1 to 5.33 cover the requirements for various types of welding consumables and electrodes. AWS 5.1 details those requirement for C S covered electrodes for shielded metal arc welding. AWS 5.01 – Filler metal procurements guidelines. AWS D 14.1 to 14.6 – These deals with various fabrication requirements for individual types of apparatus. ANSI is a private organization. It does not propose standards. It co-ordinates and forms groups to determine if standards being prepared are in public interest. ISO – International Standards Organization – Made of standard writing bodies of 80 countries. AWS publications cover following areas – Definitions and symbols, Filler metals, Qualification and testing, Welding processes, Welding applications and Safety. 101/184-- CONTROL OF MATERAILS – The inspector may be required to review documents for its compliances. He may be involved with total material control system. The Material Control
  • system must be simple. The system must have adequate checks and balance system to ensure that it does not break down. Color coding is done for material identification and tracing. High chloride marking colors damage Austenitic steel. High sulphur content harm High Nickel alloys. Alpha numeric code marking is very good for traceability but it needs lot of time and is cumbersome. ALLOY IDENTIFICATION— UNS - Unified Number system. 104/184 QUALIFICATION OF PROCEDURES AND WELDERS Welding qualifications are statement by the company verifying that the welding procedures and personnel have been tested as per codes and found to be acceptable. When people and method are tested and found acceptable it saves cost and time due to minimum rejection. CWI has a duty and responsibility to review both welding procedure and welder qualification forms to determine if they are as per code and job specifications. CWI is authorized as per code to request for re qualification if welder’s work is substandard on more occasions. PROCEDURE QUALIFICATION. – This is first step- Development of welding procedure and its performance within the procedure qualification. This is a must before welder qualification and production welding. The welder procedure qualification is preformed to show the compatibility of base material, weld or braze filler metals, process and technique. In this the welder’s ability is not a pre condition. The PQR is not meant to specifically judge the welder’s ability. There are three general approaches to procedure qualification. 1. Pre qualified procedure. 2. Actual procedure qualification testing and 3. Mock up test for special applications. AWS D --1.1 STRUCTURAL WELDING CODE.- STEEL—In this there are many procedures which are deemed qualified. The D 1.1 code contains a list of various welding processes. Base metals, Thicknesses, Joint configuration and welding techniques which are used in specific combinations are considered pre qualified. AWS D 1.1 It has 4 processes pre qualified. SMAW, SAW, FCAW and GMAW except short circuit transfer AWS D 1.1 is limited to the welding of steel 1/8” thick and greater. Essential variables are those features of the welding procedure, which if changed beyond certain limits require that a new welding procedure be established. It indicates that these variables are important enough that if varied significantly, the resulting welds may become un satisfactory. If any feature renders a welding procedure non qualified, it can be qualified by making a test weld and subjecting it to actual destructive test. The welding procedure qualification testing is done in accordance with ASME section IX.. For AWS the procedure must be qualified for each position in which production welding will take place. The performance of actual qualification tests. In the ASME system, essential variables must be stated on a WPS. This WPS will list the range of each of the essential variables, since these ranges may exceed the limit for various essential variables, this shall require many qualification tests for full coverage. The actual test conditions are recorded on a second document i.e. PQR consequently there may be numerous PQR, referring a single WPS. In ASME procedure qualification in flat position qualifies that procedure in all positions. Where as in API the procedure has to be qualified in fixed or rolled positions or both. More over qualification in either one of these positions does not qualify that procedure in other positions. SEQUENCE FOR QUALIFICATION OF A PROCEDURE 1. Select welding variables, 2. Check equipment and materials for suitability, 3. Monitor weld joint fit up as well as actual welding, recording all important variables and observations, 4. Select, Identify and remove
  • required test specimens. 5. Test and evaluate specimens, 6. Review test results for compliances with applicable code requirements. 7 Release approved procedure for production, 8. Qualify individual welders in accordance with these specifications. 9 Monitor use of the procedure during production to assure it continues to produce satisfactory results. Procedures are welding instructions and need to be readily available to welder during production. 109/184 WELDER QUALIFICATION During PQR our concern is for compatibility of materials and techniques. Once these are proven, the welder qualification is designed to judge the skill level of production welders. If welder is qualified for pipe he is automatically qualified for plate. Plate groove qualification in 3G and 4 G position will qualify that welder for all positions of the plate. Qualification in 6G and or 2G + 5G pipe position will qualify the welder for all positions of pipes except in T, K and Y connections. 6GR test position however will provide full coverage for all pipes positions and configurations. 111/184 There are various types of SMAW electrodes which are grouped according to the skill level required for these operations. Normally qualification with an electrode of a higher no. group will automatically qualify that welder for welding with any electrode of a group bearing a lower number. AWS D1.1 explains the no. of test specimens required for welder qualification. Only two bends tests are required for each welder qualification on plates. Face and root bends are used for thinner plates, while those over 3/8” require the use of side bends. Welder qualification test specimens are generally categorized as sound ness tests including bend tests, Nick break tests, and fillet break tests. For welder qualification on plate or pipe, specimens are removed according to applicable code section. For pipe coupons welded in 5G or 6G positions, specimens are removed in relation to the top of the pipe during welding. Once all the tests are satisfactory welder is qualified to work as per procedure. Necessary form as per code is filled up indicating all required information. A welder who successfully passes a qualification test is a qualified welder and not a certified welder. Most codes allow qualification to remain in effect indefinitely as long as the welder continues to successfully use the process in production. The certification may be terminated when welders leave one employer and joins other. Code generally requires that a welder be qualified by each separate employer. 112/184 Sequence for qualification of a welder. 1. Identify essential variables. 2. Check equipment and materials for suitability. 3. Check test coupon configuration and position. 4. Monitor actual welding to assure that it complies with the applicable welding procedure. 5. Select, Identify and remove required test samples. 6. Test and evaluate specimens. 7. Complete necessary paper works. 8. Monitor production welding. Welder and procedure having been qualified is not a guarantee that production weld shall be always OK. and satisfactory. The qualification welds were produced in very stringent desirable conditions where as during production the fit up, joint configuration, accessibility weather, wind, etc could introduce conditions which might increase possibility of error.
  • Welding inspector’s work starts and continues before during and after welding. Welding inspection is thus predictive and reactive. Quality conformance to specifications. Welding inspection and documents setting out specific requirement are concerned with 1. Design of joints, 2. Material, base metal and filler metal, 3.Procedures, of welding and of workmanship, 4.Preparations, joint form and dimensions. 5. Production, before during and after welding. END