American Welding Society Forum
ASME Code Case 2235 deals with the use of automated UT (AUT) in lieu of RT examination of pressure vessel welds. I have several clients that are ASME shops and I want some input from anyone with first hand (or working) knowledge of AUT in ASME shops. I have only seen this technique on pipeline projects which are covered by the API 1104 Code.
Any input is appreciated
We have considered automated UT in liue of RT on a couple of occasions in power plant applications to avoid having to stop other work in the area while radiographs were exposed. In those cases the cost for automated UT was just too high compared to RT and lost productivity to justify it's use. We would have to contract an outside company to perform automated UT, and the cost is high. I suppose if you already own the equipment and have people qualified to do the data analysis, perhaps the cost could be justified. In a fab shop, the RT shots can be scheduled for meal breaks or shift changes to lessen the impact on other work and the RT capability is usually readily available. I don't see a cost savings, and you have to deal with the "overcalls" with UT indications.
AUT has been used for years in US nuclear power plants. One application that I have seen is for the detection of IGSCC.
That's right. However, another place where AUT has been widely used in power plants for years is in Reactor Vessel examinations.
AUT is much more sensitive than RT, particularly on mechanized welds where you may have other than normal bevel angles. However those overcalls mentioned earlier are usually attributable to indications missed by RT due to varying sensitivities of the two methods.
The problem most people have with AUT is that they utilize normal acceptance standards developed with RT in mind. Some people call it workmanship acceptance standards. Indications are evaluated based on length only. Due to the added sensitivity, when using AUT one should develop an alternate acceptance criteria based on length and vertical height of the flaws. This would eliminate most of these overcalls and prevent any unnecessary repairs.
If you are going to utilize UT for Inservice examinations, what better way to establish a baseline than with AUT?
Don't be afraid of AUT. It is your friend and it is there to help you.
Don't misunderstand me - I like automated UT, especially for IGSCC exams, RPV seam welds and nozzle exams. The downside is the cost of automated UT vs. RT for fabrication welds that are easily accessible and the lack of suitable UT acceptance criteria for fabrication welds in the ASME code. The cost of an automated UT exam of a reactor vessel is greater than $1 million, automated UT of BWR feedwater nozzles exceeds $500,000, and a single pipe weld could easily cost $20-30,000. I don't see that being cost effective unless there is a severe hardship with doing RT, such as limited access for source or film placement, harsh working environment (e.g. radiation dose rates), or severe loss of productivity due to having to stop other work in the area while RT is performed. Also, while ASME XI has been very thorough at addressing UT personnel qualification, procedure qualification and acceptance criteria, the fabrication sections (I, III, VIII) have not kept up and don't address UT well enough to prevent the problems with overcalls. So, I'm not afraid of using UT provided it is cost effective for the specific application and suitable evaluation criteria exist.
Marty, please. I meant nothing by my statement about overcalls.
But I have seen lots of repairs being performed because clients have not adopted any form of ECA acceptance criteria. Some of these indications were so small in vertical height that they probably were not detectable by RT. However due to their length, they were rejectable.
You make a very good point, however, about the cost involved. It is expensive because the equipment is expensive as are the AUT operators.
I believe that if utilties were to invest into the reserach, and get it accepted, they could come up with alternate ECA acceptance criteria that could in the long run save them money.
Such as is done with API 1104 Appendix A for pipelines. CTOD testing is performed to provide data for the development of alternate acceptance criteria for AUT.
Thanks for all the responses. The costs of inspections was really a suprise. Is that due to fact that these are inservice inspections? Does anyone know the cost of potrable equipment? How much do inspection firms charge per hour?
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