Asme Code Case 2235 Pdf
Technical Basis for ASME Section VIII Code Case 2235 on Ultrasonic Examination of Welds in Lieu of Radiography.
Dave Cowfer
. ASME CODE CASE 2235-9 Foreword Some years ago Asme Code has introduced the possibility to substitute the Radiography by Mechanized Ultrasonic Inspection of welds from the minimum thickness of 13 mm and on. The fact that the possibility is still limited in a Code Case, apart from Section VIII Div. II were is now covered under chapter 7, gives the idea that the problem is still under careful examination. Too often the document is interpreted by the Inspection Agencies or clients with original approach, causing lot of problems to the Manufacturer of pressure vessels that do not find a well defined position in the code that can help to interpret the document.
Present paper takes into consideration some applications were many Manufacturers after a period of enthusiasm for the possibility to get rid of Radiation with all the annexed problems, having the possibility to give more complete information on the results of an inspection, using the most recent equipment available, are now considering to come back to the old Radiography. Some points that give raise to more frequent dispute are here reported; for easy presentation the original text is reported and some comments are associated for consideration and possible discussion from the audience.
The conclusion is that it is easier to discuss and to obtain the approval of the Radiography system even if the results obtainable with ultrasonics are more complete and precise. The situation In principle the Code Case states that UT is accepted in lieu of radiography starting from thicknesses of 13 mm and over, provided that (only the most important items for our scope are reported here, toghether with short comments): No Comment N. In this case the thickness of defect need not to be measured? What about the position? In case of Tofd technique what to do for defects close to surface? This apply also for C-B scan and phased array.
Praxair
(1)(a) manually? But without unprocessed recordable way (1)(b)again see (1)(a) above valid for all (1),(2),(3) Difficult to interpret, come back to radiography? Difficult to evaluate and not automatically recorded in unprocessed way The three NDT systems considered do not detect the depth of a defect with the precision requested N. Elements for consideration On the basis of the above simple considerations it appears that, after long time, the problem of accepting UT in Lieu of RT is still in a discussion stage and that the acceptance of any system is still depending from the Company requesting the inspection and from the mood of the Inspector or Third Party Agency Representative. The demonstration of satisfactory performance is very difficult, when inspecting pipes of large thicknesses (more than 50 mm) and small diameters, particularly in Pipe-to Flange or Pipe to Elbow connections. In some cases Inspectors from well known Companies have requested the validation of the system by means of blind tests performed on samples specifically prepared to verify the detection of artificial reflectors that for their nature and position would not normally be encountered in practice.
In other cases a modelling of scan plan prepared to detect, in the most unfavorable condition, the maximum defect to be found, were preliminary evaluated in terms of probability of detection by software, obtaining even different results from the ones used from two different Inspection Agencies. The conclusion is that more and more Constructors prefer to come back to RT inspection for big thicknesses because what can be seen is often very poor and do not give raise to endless dispute.