Can non-destructive testing methods TOFD+UT+MT replace RT?
Thread Content
During the manufacturing of static equipment, non-destructive testing is required to meet the standards of 100% RT grade II compliance + 100% UT grade I compliance as specified in the design. However, due to the thick walls, large diameter of the equipment, and tight schedule, the current requirement is 100% TOFD grade II compliance + 100% UT grade I compliance + 100% MT grade I compliance. During implementation, the non-destructive testing agency stated that 100% TOFD includes 100% UT (for the thickness of the TOFD blind area) + 100% MT. Therefore, is it necessary to conduct 100% UT on the entire weld thickness again? If 100% UT is carried out, it will incur additional costs, as TOFD only covers UT for the thickness of the TOFD blind area; however, the design drawings require 100% UT. Can TOFD replace UT in this case? Is it feasible to perform UT only on the thickness of the blind area? Help!
This post was last edited by fzujunru on 2020-10-29 at 14:12. The requirement for both RT and UT is due to their complementary nature: RT has a low detection rate for surface defects and is not sensitive to cracks, whereas TOFD and UT have similar capabilities in detecting volumetric and surface defects. In practice, UT is often used for rechecking the defects detected by TOFD.
I hope there are professionals who can answer. I also learned it by following**
Changing the non-destructive testing method requires written consent from the original design entity.
Yes, it’s just that what we wrote is 100% TOFD + 100% UT + 100% MT; thus, the non-destructive testing company and we have two different interpretations of this
Firstly, for the original design of RT+UT, it is necessary to determine whether the material of the equipment is high-strength steel or another material that requires different testing methods as specified in requirement 150. Secondly, TOFD and UT are gradually becoming two separate testing methods; UT involves ultrasonic testing that does not generate records
Theoretically, the designed structure should take into account 100% detection or supplementary detection in areas with blind spots; it seems that the changes you made aren’t very scientific, as only one type of detection is now available
According to the design requirements, non-destructive testing shall consist of 100% RT at grade II with satisfactory results, plus 100% UT at grade I with satisfactory results. In other words, the intention behind the design is to ensure 100% RT at grade II along with 100% UT re-inspection at grade I. It is acceptable to use 100% TOFD grade 2 pass + 100% UT grade 1 pass as a substitute. It is not acceptable to perform UT only on the thickness of the blind area.
RT+UT requires the complete detection of both horizontal and vertical defects; those who are not familiar with TOFD mainly focus on whether TOFD can achieve the same results as RT. Or it can directly achieve the RT+UT effect.
I don’t think so; the main reasons are to save money and time. However, the safety of such large-scale equipment still needs to be given top priority.
Yes, it mainly saves the cost of a full-thickness UT test