With all due respect, the most common causes for this kind of defect are:
1. Too narrow root gap, accessibility difficult
2. Too large gap, volume contraction effect during cooling becomes significant
3. High welding speed
Στις Δευ, 25 Μαρ 2019 στις 4:17 π.μ., ο/η steel_microbe <matschka69@gmail.com> έγραψε:
--In the future, you can have your welder deposit the root but leave 2 tiny areas open or unfused. Say at 9:00 & 3:00. and then use a flashlight in 1 window to showthe opposite side root pass. These windows should be left open after the root so you can view the 2nd. pass that is being welded. The 'viewer' can talk to the welderand let him know if his 'heat' is ok, 'no reconsuming of root. He may have to speed up or slow down to prevent reconsumming the root. If the welders 'heat' is causinghim to reconsume the 'root' pass, he will get 'suck back' or also called root concavity. I have seen this many times. A welder will deposit a great root pass, he has looked back with a flashlight and viewed the root pass before he closes up the root pass. He then finishes the weld and it is RT'd. The film is reviewed and guess what? unacceptable root concavity.The welder will argue against this finding because he inspected the root pass before he completed the root. On one Nuclear shut down job we had the opportunity to cut out a small section of the pipe including the weld that was rejected due to excessive root concavity.This sample was shown to the welder and he was 'amazed' quite surprised to the point of apologizing to me and others. Needles to say from then on every pipe weld was left open thru the 2nd. pass for assuring a root pass did not have this 'excessive concavity'. We showed this weld to all the welders andfitters and made a 'learning lesson' out of it. I have over 60 years of welding expertise. I know what goes where and why. I know what works and what will not.The company I worked for has included this technique in their own Welding Standards. I cannot pull up this picture which Ibratech has provided, but the converstions suggest root concavity. If it is located in one small spot or area it can be repaired very easily. Simply grind the area back to it's original groove configuration including the 1/8in. gap which I would prefer and the company I worked for mandated. Reweld using your best welder or the one who has experiencedoing repairs.
On Thursday, March 21, 2019 at 5:28:30 PM UTC-5, ibratech wrote:Gents,I am getting the attached image in boroscope inspection at root. But RT not showing any density variation or undercut. Please give your comment on it.
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Dr. Georgios Dilintas,
Dipl. Ing. In Aeronautic and Space Engineering
Ph.D in Mechanics of Solids - Computational Mechanics
A.I.S, A.N.I, IRCA Lead Auditor
Welding, Stress Analysis, Corrosion, QA/QC, Failure Analysis, Risk Analysis
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