1、 PFI Standard ES-48 |Denotes Revision (Revised December 2013) RANDOM EXAMINATION Prepared by Pipe Fabrication Institute Engineering Committee All PFI Standards are advisory only. There is no agreement to adhere to any PFI Standard and their use by anyone is entirely voluntary. Copyright by PIPE FABR
2、ICATION INSTITUTE Dedicated to Technical Advancements and Standardization in the Pipe Fabrication Industry Since 1913 USA 511 Avenue of Americas, # 601 New York, NY 10011 CANADA 655, 32ndAvenue, # 201 Lachine, QC H8T 3G6 WEB SITE www.pfi-institute.orgPFI Standard ES-48 |Denotes Revision (Revised Dec
3、ember 2013) Random Examination Expectations, Guidelines and Methodology 1. Scope 1.1. Codes and specifications often require that welds be subjected to spot or random radiography, ultrasonic or other examination methods. The purpose of this standard is to: 1.1.1. Examine the expectations, effectiven
4、ess and limitations of random examination. 1.1.2. Identify common industry practices and methods for specifying random examination. 1.1.3. Provide guidance in establishing and defining the size of a lot to be subjected to random examination, focusing on the ASME B31.3 use of the terms “lot” and “kin
5、d of item.” 2. Definitions 2.1. Commonly used extents of examination are defined as follows: 2.1.1. Random examination: complete examination of a percentage of a specified kind of item in a designated lot of piping 2.1.2. Spot examination: a specified partial examination of a weld or specified group
6、 of welds (e.g. 1 six inch spot in each 50 feet of weld by a particular welder) 2.1.3. Random spot examination: a specified partial examination of a percentage of a specified kind of item in a designated lot of piping 2.1.4. This standard uses the term ”random examination” to represent all examinati
7、on methods such as radiography and ultrasonic or other examination that may be used in order to avoid excessive repetition of these inspection method names throughout this standard. 3. Expectations, effectiveness and limitations of random examination 3.1. Random examination of welds in a piping syst
8、em will not ensure that all the welds in that system will be of the same quality level as the welds that were examined. For example, if 10 welds in a piping system containing 100 welds are examined and accepted using random radiography, the remaining 90 welds may contain rejectable flaws that would
9、have been disclosed if additional welds had been radiographed. If all rejectable weld flaws must be eliminated from a given piping system, then examination of 100% of the welds in that system must be performed1. More simply put, to insure that welds are free of rejectable flaws, 100% of those welds
10、must be examined, repaired as necessary and then reexamined. 3.2. Random examination of welds is an effective quality control tool when properly implemented. 3.2.1. When random examination is used to check the quality of the welders work, that examination provides feedback to the welder showing that
11、 the work is or is not satisfactory. If the work is not satisfactory, the welder and/or the welding supervisor can take corrective steps to improve weld quality in subsequent work; such steps can include the full range of changes from increased attention, to initial fit-up, to replacement of the wel
12、der. This will improve the quality of subsequent welds. 3.2.2. For this process to work properly, it is critical that examinations be made, (and timely feedback provided to the welder), contemporaneously with the work being done. The sooner the welder learns that his weld requires repair, the sooner
13、 he can take corrective action. 1See ASME B31.3 para. 344.1.3, footnote 3 and ASME section VIII Div 1, UW-52 footnote. PFI Standard ES-48 |Denotes Revision (Revised December 2013) 4. Specifying Random Examination 4.1. The method and extent of examination and acceptance criteria to be applied must be
14、 clearly defined in the standard or specification and be agreed upon prior to the start of work. This is standard industry practice that is well established in various welding standards such as the ASME B31 Code for Pressure Piping, ASME Section VIII, Unfired Pressure Vessels, and the AWS D1.1, Stru
15、ctural Welding Code - Steel. For example, ASME B31.1, paragraph 136.3.1, specifies: “The degree of examination and the acceptance standards beyond the requirements of this Code shall be a matter of prior agreement between the manufacturer, fabricator or erector and the Owner.” 4.2. When performing r
16、andom examination, the method of examination (e.g., radiography in accordance with ASME Section V, Article 2) and the acceptance criteria (e.g., ASME B31.1, paragraph 136.4.5) are straightforward and simple to define in the contract documents. 4.3. When random examination is specified, the extent of
17、 random examination must be clearly defined in the contract documents. Random examination can be applied to: 4.3.1. Circumferential butt and miter welds on a project. 4.3.2. Circumferential butt and miter welds within specific line classes or systems on a project, 4.3.3. Circumferential butt and mit
18、er welds within particular parts of systems (e.g., high-pressure parts of a steam system) 4.3.4. Circumferential butt and miter welds in specific locations (e.g., piping inside buildings) 4.3.5. Other schemes that satisfy the Owner or his engineer. 4.3.6. Volumetric examination is not normally appli
19、ed to nozzle or branch connection welds or to fillet welds. 4.4. When the purchaser wishes to impose additional random examination, and the applicable code does not specify random examination, the following is recommended for inclusion in the purchasers specification: “Random Radiography and accepta
20、nce criteria shall be in accordance with the requirements of ASME B31.3, paragraph 341.4.1(b). Acceptance criteria shall be in accordance with Table 341.3.2, Normal Fluid Service, with progressive sampling in accordance with paragraph 341.3.4.” 5. Defining Random Examination when ASME B31.3 is appli
21、cable 5.1. The following are important points to recognize when ASME B31.3, Process Piping, is the applicable Code. 5.1.1. For Normal Fluid Service piping, Paragraph 341.4.1(b) requires that not less than 5% of circumferential butt and miter groove welds be examined fully by random radiography or by
22、 random ultrasonic examination. Normal Fluid Service is the applicable fluid service category unless another Fluid Service Category (e.g., Category D, Category M, Severe cyclic, etc) or a greater extent of examination is specified for a system by the engineer in the contract documents. 5.1.1.1. Rand
23、om Examination is to be performed on a lot basis. Once the percentage of welds in a lot are examined and accepted and the welds representing the work of each welder in that lot have been examined and accepted, all remaining welds in that lot (i.e., those that were not examined) are Code-acceptable p
24、rovided they are visually acceptable and pass hydrostatic testing. See paragraph 341.3.1. 5.1.1.2. Since B31.3 places responsibility for performing examination on the Fabricator or Contractor who is doing the welding, lot selection is the prerogative of the Fabricator or Contractor in the absence of
25、 arrangements in which a lot is established by contract. B31.3 recognizes that lot selection can be a source of dispute and suggests2that the quantity or extent of a designated lot should be established by agreement between the contracting parties before the start of work. See Section 6 for various
26、methods of defining a lot. 2See paragraph 344.1.3, footnote 2. PFI Standard ES-48 |Denotes Revision (Revised December 2013) 5.1.1.3. Since B31.3 places responsibility for performing examination on the Fabricator or Contractor who is doing the welding, lot definition is the prerogative of the Fabrica
27、tor or Contractor in the absence of contractual arrangements in which a lot is established by contract. 5.1.2. The welds to be examined must include the work product of each welder, whose welds are part of any designated lot, but B31.3 does not require that the given percentage of each welders work
28、within a lot be examined. 5.1.3. When a weld is rejected, B31.3 paragraph 341.3.4 requires “progressive sampling” of other welds made by the welder who made the defective weld. Welds made by other welders within the lot that have either been examined and accepted or have not been examined would not
29、be subject to progressive sampling. 5.2. Should the purchaser or his representative demand additional nondestructive examination within a lot after that lot of welds has been accepted, such additional examination is outside the provisions of B31.3. Defects found by this additional examination shall
30、be repaired and the weld re-examined. The cost of any additional examination, and any subsequent repairs and re-examination, shall be the responsibility of the organization requiring the additional examination. Approval of the customers contracting officer may be required for increases in the extent
31、 of examination since such examination would usually be compensable changes to the contract. 6. Establishing a Lot 6.1. Contract requirements for establishing lots or for selection of welds to be examined should be agreed upon by the contracting parties. When the purchaser will be responsible for se
32、lection of the random welds in a lot, the purchasers representative will need to be readily available to avoid impeding work flow. The process of selection should also be included in such agreement, (e.g., select from the list of welds in a lot, select the weld(s) after visual examination, etc.) 6.2
33、. The welds in a lot do not need to be of the same material, thickness or size. Butt welds and miter welds do not need to be segregated into different lots, and more than one welding process may be included in a lot. 6.3. In defining a lot, the fabricator/contractor should consider the following: 6.
34、3.1. The lots should be of a size that can be easily managed. Small lots may result in increased cost because paperwork will increase and the total number of welds examined on the project will increase beyond the percentage required. Conversely, large lots lead to increased risk when progressive sam
35、pling is required. 6.3.2. Welds should be examined shortly after the required lot size has been achieved in order to obtain the desired effect on the quality of the work. 6.3.3. It may be necessary to examine the initial welds made within each lot prior to the completion of all the welds within that
36、 lot, to provide timely feedback. 6.3.4. The results obtained in examination of one lot should not be considered in the evaluation or extent of examination applied to any other lot. 6.3.5. A tracking method that clearly documents welds in each lot should be established. 6.3.6. Welds selected for eac
37、h lot must fall into the same percentage of examination. 6.4. Some lot definitions are show below. 6.4.1. Daily: All the welds completed by all welders, and are accepted by visual examination on any day shall be considered a lot. The number of welds to be examined shall be calculated based on the si
38、ze of the lot and the percentage of welds that are required to be examined. 6.4.2. Daily Multiple lots: All the welds completed by all welders, and accepted by visual examination on any day shall be broken up into separate lots and each lot examined individually (e.g., 65 welds are completed in a da
39、y; if the lot size is 20, those 65 welds shall be separated into 4 lots of a convenient sizes of 20 or fewer and the welds to be examined shall be selected from each lot). If the required number of welds to achieve the required lot size has not been obtained, the welds that have been completed each
40、day shall be considered a lot. PFI Standard ES-48 |Denotes Revision (Revised December 2013) 6.4.3. By Welder: Only the welds of a single welder are included in the lot. When the welds made by a welder achieve the required lot size, that group of welds shall be considered a lot. Since more than one w
41、elder may make a weld, that weld shall be included only in one welders lot. 6.4.4. Truck Load: All welds on all of the assemblies to be loaded on a single truck shipment may be considered a lot. Acceptance of the whole lot should be completed prior to loading the truck. 6.4.5. All Welds on a Job: Al
42、l the welds on a job may be considered a lot. This option should not be selected unless the project is very small. 6.4.6. Spool Grouping: Each project shall be subdivided into “lots“ as required for convenience and flow of work through the shop. The “lot“ may consist of different piping systems with
43、 the same percentage requirements for random radiography. Only piping with the same radiographic percentage requirements (e.g. 5% and 20% systems) should be included in the same “lot“. 6.4.7. All the Welds in a Piping System or Line: When drawings identify the customers piping system, all welds in e
44、ach system can be considered a lot. Another alternative is to choose lots by line or group of lines. This option is generally only suitable for field welding. In a shop environment, this method is discouraged because it increases costs due to impeded work flow, added material handling and delayed de
45、livery. 6.4.8. All Welds in a Room or other Easily-defined Space: Field work only. 6.4.9. Welds along a run until the required number is reached. Field work only. Not suitable for sizes and wall thicknesses where achieving a lot of a particular size takes an extended period of time. 6.5. Shipping of
46、 Lots: For shop fabrication, no item in a lot shall be shipped before the required examination of that lot is completed and that lot has been accepted. 7. Documentation of Sampling 7.1. Welds making up lots should be documented concurrently with the progress of fabrication. Joints should be logged a
47、s final visual inspection is completed for each spool piece or as erection welds are made. Any form of tracking and documenting lots is acceptable provided: 7.1.1. The welds which make up the lot are clearly identified 7.1.2. The number of welds from each welder is clearly identified 7.1.3. The weld
48、(s) selected for examination are clearly identified 7.1.4. All of the requirements for initial selection and progressive selection have been met. CURRENT INDEX OF 2014-2015 PFI STANDARDS A complete list of PFI members and available membership CHARTER MEMBERS CONTRACTOR MEMBERS ASSOCIATE MEMBERS AFFILIATE MEMBERS HONORARY MEMBERS Associate and Affiliate member contributors Walter Sperko Sperko Engineering Services, Inc. Greensboro, NC Thomas Warrelmann Victaulic Company of America Easton, PA Sheryl Michalak Welding Outlets, Inc. Houston, TX PFI Standards and Te
