[en] Welded joints in steam lines in the Forsmark 1 BWR reactor has been investigated. Folds were notised in the bottom of welds on both thin and thick pipes. It has been found that a high degree of precision in fabrication is important to avoid folds. This means good moulds, minimum displacement of edges and suitable velding technique. It is difficult to detect the folds. Radiography gives a poor result. Ultrasound is the most useful method. Sometimes testing with magnetic powder might be used. Calculations show that crack growth of the folds is very slow. A problem is the difficulty to determine the depth of the folds with nondestructive methods. (K.K.)