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Non-destructive testing handbooks
BOOK REVIEWS
Non-destructive testing h a n d b o o k s G e n e r a l D y n a m i c s , C o n v a i r Division, 1967 A s e t of ' p r o g r a m m e d i n s t r u c t i o n ' and ' c l a s s r o o m t r a i n i n g ' handbooks d e s i g n e d f o r the t r a i n i n g of ndt i n s p e c t o r s and o p e r a t o r s . T h e s e v o l u m e s c o v e r the following a s p e c t s of ndt p r a c t i c e : (1) I n t r o d u c t i o n (2) Eddy c u r r e n t t e s t i n g (3) M a g n e t i c p a r t i c l e t e s t i n g (4) U l t r a s o n i c t e s t i n g (5)
Liquid p e n e t r a n t t e s t i n g
INTRODUCTION One is s u r p r i s e d when f i r s t opening the i n t r o d u c t o r y book to find the left h a n d p a g e s p r i n t e d u p s i d e down. T h i s i s not a p r i n t e r ' s e r r o r , but i s p a r t of the t e a c h i n g technique i n c o r p o r a t e d in the book. At e a c h s t a g e the r e a d e r i s p o s e d q u e s t i o n s and a s a r e s u l t of h i s a n s w e r i s r e f e r r e d to a new page in the book w h e r e t h i s p a r t i c u l a r a n s w e r i s d i s c u s s e d , If the a n s w e r i s not c o r r e c t the r e a d e r i s s e n t to c h o o s e another, The book then goes on to show how a l l d e f e c t s can be c a t e g o r i s e d a s d i s c o n t i n u i t i e s and g i v e s s o m e v e r y obvious e x a m p l e s of t h e s e in the f o r m of q u e s t i o n s which could only be a n s w e r e d i n c o r r e c t l y by a m o r o n . The next s e c t i o n c o n t a i n s a d e s c r i p t i o n of the s t e e l - m a k i n g p r o c e s s and shows c l e a r l y how i n c l u s i o n s , p o r o s i t y a n d pipe o c c u r . T h i s o c c u p i e s 27 p a g e s but could h a v e b e e n c o n d e n s e d into f a r fewer,
The f i r s t book s t a r t s by s t r e s s i n g that only d e f e c t s r e a c h i n g the s u r f a c e can be d e t e c t e d by t h i s m e t h o d and e x p l a i n s the i m p o r t a n c e and m e t h o d s of cleaning. A w a r n i n g i s given about the toxic and i n f l a m m a b l e n a t u r e of s o m e c l e a n i n g fluids and of the r i s k of closing d e f e c t s by shot b l a s t i n g . The q u a l i t i e s r e q u i r e d of a dye p e n e t r a n t a r e d i s c u s s e d and the c l a s s i f i c a t i o n into f l u o r e s c e n t and n o r m a l l y v i s i b l e dyes i s explained. The use of b l a c k light is mentioned, but t h i s i s s a i d to b e a h a r m l e s s r a d i a t i o n b e t w e e n the v i s i b l e and the u l t r a - v i o l e t . Since the two a r e a d j a c e n t in the s p e c t r u m t h i s n e e d s a m p l i f i c a t i o n , and a w a r n i n g should be given of the p o s s i b l e d a n g e r s of e x c e s s i v e e x p o s u r e to u l t r a - v i o l e t r a d i a t i o n if adequate f i l t r a t i o n i s not used. T h e r e follows the next step of application, and w a r n i n g s a r e given about allowing sufficient dwell t i m e and using the p e n e t r a n t b e t w e e n fixed t e m p e r a t u r e l i m i t s . R e m o v a l of e x c e s s p e n e t r a n t i s c o v e r e d in c o n s i d e r a b l e d e t a i l and c a r e ful d i s t i n c t i o n i s m a d e between the m e t h o d s u s e d for d i f f e r ent types of p e n e t r a n t . The c o r r e c t u s a g e of both wet and d r y d e v e l o p e r s i s dealt with v e r y well and w a r n i n g s a r e given of the p i t f a l l s which m a y be e n c o u n t e r e d . T h e final s t e p s of i n s p e c t i o n and cleaning a r e a c c o m p a n i e d by a c l e a r s e l e c t i o n of i l l u s t r a t i o n s showing the a p p e a r a n c e of p e n e t r a n t in v a r i o u s t y p e s of defect. The a d v a n t a g e s of u s i n g m a g n e t i c and f i l t e r e d p a r t i c l e t e s t s a r e then explained followed by a long s e c t i o n which is p a r t i a l l y a r e c a p i t u l a t i o n and p a r t i a l l y an e x e r c i s e in applying what h a s b e e n l e a r n e d to a c t u a l p r o b l e m s . The final p a r t of the book shows typical i n s p e c t i o n s e t - u p s and d e s c r i b e s s p e c i a l p e n e t r a n t s which m u s t b e u s e d when c o m p a t i b i l i t y is a p r o b l e m . The C l a s s r o o m T r a i n i n g Handbook on liquid p e n e t r a n t t e s t i n g I found to b e laid out in a m a n n e r m u c h m o r e to m y liking and to contain c o n s i d e r a b l y m o r e d e t a i l e d i n f o r m a t i o n .
The next page c o n t a i n s four s e c t i o n s e a c h with a w o r d m i s s ing o r p a r t i a l l y m i s s i n g and an a r r o w pointing o v e r l e a f , The f i r s t i n c o m p l e t e s t a t e m e n t i s ' T h e r e a r e - arrows on t h i s e n t i r e page (write in the c o r r e c t numl~er of a r r o w s ) ' Comment is superfluous, If one i s not put off by the n a i v e t y of s o m e of what h a s gone b e f o r e and r e a d s on, a useful section follows in which the n a t u r e of d e f e c t s in b a r stock and p l a t e i s e x p l a i n e d and the r e a d e r i s shown how t h e s e o r i g i n a t e f r o m the d e f e c t s in b l o o m s to b e c o m e s e a m s , s t r i n g e r s , etc. P r o b a b l y the b e s t s e c t i o n in the book c o n c e r n s forging and c a s t i n g p r o c e s s e s and the d e f e c t s which a r e likeIy to occur, with c l e a r e x p l a n a t i o n s of the f o r m a t i o n of laps, b u r s t s , hot t e a r s and cold s h u t s . T h e r e a r e a m p l e c l e a r i l l u s t r a t i o n s of all t h e s e conditions. A f t e r i n v e r t i n g the book, one r e a d s b a c k t h r o u g h pages c o n c e r n e d with f u r t h e r types of c a s t i n g defects, The f o r m a t i o n of s l u g s and d e f e c t s in w e l d s in tubing i s explained, followed by e x t r u s i o n d e f e c t s and g r i n d i n g cracks, D e f e c t s due to h e a t t r e a t m e n t a r e m e n t i o n e d and explosive f o r m i n g and the r e s u l t a n t d e f e c t s a r e also c o v e r e d . E x a m p l e s a r e quoted of the i m p o r t a n c e of s t r e s s r a i s e r s in i n i t i a t ing d e f e c t s . The final s e c t i o n d e a l s c l e a r l y with the f o r m a tion of c o m m o n d e f e c t s in w e l d s b a c k e d up by adequate illustrations.
A f t e r an i n t r o d u c t i o n giving t e s t i n g philosophy the g e n e r a l p r i n c i p l e s a r e e x p l a i n e d in a c o n c i s e m a n n e r , i l l u s t r a t e d by c h a r t s of the v a r i o u s p r o c e s s e s . The following two c h a p t e r s list the e q u i p m e n t and m a t e r i a l s r e q u i r e d a n d d e s c r i b e the t e c h n i q u e s for u s i n g t h e m . A useful table i s i n c l u d e d giving t i m e s for v a r i o u s p a r t s of the p r o c e s s e s to d e t e c t a wide v a r i e t y o~ flaws in m a n y d i f f e r e n t m a t e r i a l s . W a r n i n g s of f a l s e i n d i c a t i o n s a r e c o n t a i n e d in the c h a p t e r on i n t e r p r e t a t i o n of r e s u l t s and this is c l e a r l y i l l u s t r a t e d with p h o t o g r a p h s of defective p a r t s . The f o r m a t i o n of c r a c k s in a r t i f i c i a l t e s t b l o c k s is d e s c r i b e d in the section on quality c o n t r o l of p e n e t r a n t s , e m u l s i f i e r s and d e v e l o p e r s . The book c o n c l u d e s with a s e c t i o n which i s m o s t valuable, but would s e e m b e t t e r s u i t e d to a g e n e r a l book on t e s t i n g since it c o m p a r e s the e f f e c t i v e n e s s of d i f f e r e n t ndt techniques for each type of defect. I do not think anyone could q u a r r e l s e r i o u s l y with the r e c o m m e n d a t i o n s and once a g a i n it is v e r y e f f e c t i v e l y i l l u s t r a t e d with e x a m p l e s of defective p a r t s which m u s t have taken a long t i m e to collect. T h i s s e c t i o n should be r e a d by any ndt p r a c t i t i o n e r who i s i n c l i n e d to be p a r t i s a n about his f a v o u r i t e technique.
The addition of i n s t r u c t i o n in how d e f e c t s a r e f o r m e d to an ndt c o u r s e i s well w o r t h w h i l e and should i n c r e a s e the value of an I n s p e c t o r who m a y b e able to a s s i s t with the e l i m i n a tion of d e f e c t s a s well a s t h e i r detection,
T h e f i r s t volume c o v e r i n g u l t r a s o n i c t e s t i n g i s e n t i t l e d ' B a s i c P r i n c i p l e s ' and i n t r o d u c e s the r e a d e r to the s u b j e c t via the m e d i a of a s e r i e s of b a l l s i m p a c t i n g upon each o t h e r in t u r n and v i b r a t i o n of p l a t e s s t r u c k with a h a m m e r . The c o n c e p t s of a cycle of oscillation, f r e q u e n c y and p e r i o d a r e c l e a r l y explained. T r a n s m i s s i o n of sound through v a r i o u s m e d i a i s then c o v e r e d , but the p r o b l e m s of a n a i r b a r r i e r a r e not too c l e a r l y e x p l a i n e d and one could f o r m the i m p r e s s i o n that the change of v e l o c i t y was the main p r o b l e m . The s t a t e m e n t that ' a i r does not do a v e r y good job of t r a n s m i t t i n g sound' i s d e m o n s t r a b l y u n t r u e and m o r e could have b e e n made of the i n t e r f a c e p r o b l e m .
LIQUID P E N E T R A N T TESTING Liquid p e n e t r a n t t e s t i n g i s c o v e r e d in two handbooks, the f i r s t a p r o g r a m m e d i n s t r u c t i o n book s i m i l a r in style to the i n t r o d u c t o r y book, and the o t h e r i n t e n d e d for c l a s s r o o m training,
ULTRASONIC TESTING
n o n - d e s t r u c t i v e t e s t i n g F e b r u a r y 1970
59
A b r i e f d e s c r i p t i o n of a t r a n s d u c e r , its b e a m d i v e r g e n c e , the n e a r and f a r z o n e s and the m e a n i n g of wavelength a r e all adequately c o v e r e d . The d e s c r i p t i o n g i v e s the i m p r e s s i o n that attenuation in signal o c c u r s only in the far zone, but this may not be intended. The r e a d e r i s then i n t r o d u c e d gradually to the laws g o v e r n i n g p r o p a g a t i o n of u l t r a s o u n d in m a t e r i a l s and a c r o s s i n t e r f a c e s and v e r y c l e a r e x p i a n a t i o n s a r e given of the d i f f e r e n t types of wave and how they a r e g e n e r a t e d . It i s s u r p r i s i n g that although the d e p e n d e n c e of t r a n s m i s s i o n a c r o s s an i n t e r f a c e on a c o u s t i c a l i m p e d a n c e is mentioned, the f o r m u l a is not given in the s a m e way a s most others, The book e n d s with explanations of p u l s e r e f l e c t i o n , through t r a n s m i s s i o n and r e s o n a n c e t e s t i n g and points out the p r o b l e m s of p o o r s u r f a c e coupling and s o m e of the ways in which s p u r i o u s e c h o e s can occur. The g e n e r a l layout of [he book i s s i m i l a r to the i n t r o d u c t o r y volume including the self-testing sections, The second p r o g r a m m e d handbook on u l t r a s o n i c t e s t i n g b e gins with a d e t a i l e d introduction to the d i f f e r e n t types of u l t r a s o n i c contact t r a n s d u c e r s and e x p l a i n s how they a r e coupled to s p e c i m e n s . P o s s i b l y a m i s p r i n t i s the use of the lower c a s e ' m ' f o r the p r e f i x ' m e g a ' and this will no doubt be c o r r e c t e d in l a t e r editions, The use of v a r i o u s t y p e s of l e n s e s f o r b e a m shaping and defect r e s o l u t i o n i s well explained but the s t a t e m e n t that ' a c o l l i m a t o r a d d e d to the f r o n t of a t r a n s d u c e r r e d u c e s the b e a m s p r e a d and p r o d u c e s a s m a l l e r and s t r a i g h t e r sound b e a m ' is not c o r r e c t , s i n c e the b e a m s p r e a d following a b e a m limiting a p e r t u r e m u s t be g r e a t e r than f r o m a l a r g e r t r a n s d u c e r face. Wheel and b u b b l e r t r a n s d u c e r s a r e a l s o c o v e r e d . The s e c t i o n on coupling m a t e r i a l s can a l s o be m i s leading s i n c e although the s t a t e m e n t that a coupling fluid should be midway in a c o u s t i c i m p e d a n c e b e t w e e n the t r a n s d u c e r and s p e c i m e n i s n e a r l y enough c o r r e c t , it i s not made plain that this condition is h a r d l y e v e r a p p r o a c h e d in practice. V a r i o u s d i f f e r e n t t e s t blocks a r e c o v e r e d and w a r n i n g s a r e given of the d i f f e r e n c e s between e c h o e s f r o m r e a l and a r t i f i c i a l d e f e c t s . The r e s t of the book d e s c r i b e s v e r y adequately the d i f f e r e n t c o n t r o l s on an u l t r a s o n i c t e s t set and how they should be used. All t y p e s of equipment a r e v e r y fully c o v e r e d a s is the p r e s e n t a t i o n of i n f o r m a t i o n on a facsimile plotter,
radiation h a z a r d . The implication could be drawn that this h a z a r d e x i s t s with o t h e r f o r m s of u l t r a s o n i c inspection. At each a p p r o p r i a t e point in the book the use and c o n s t r u c t i o n of a p p r o p r i a t e t e s t blocks is always included. The u l t r a s o n i c c l a s s r o o m training handbook, a s with the o t h e r books of this type, c o n c e n t r a t e s the contents of the p r o g r a m m e d i n s t r u c t i o n handbooks into a f o r m which this r e v i e w e r finds m o r e a c c e p t a b l e . It also t a k e s m a t t e r s f u r t h e r and adds additional useful m a t e r i a l . It would s e e m that s o m e of the i n t r o d u c t o r y p a r a g r a p h s have been s h o r t e n ed in a m a n n e r leading to s t a t e m e n t s which could e a s i l y be m i s i n t e r p r e t e d . A s an example, the s t a t e m e n t is made that ' N o r m a l adults may h e a r n o t e s of f r e q u e n c i e s higher than 16, 000 c y c l e s p e r s e c o n d (16 Kc) - - up to about 20,000 c y c l e s p e r second (20 Kc)'. Without additional definition of the l i m i t s of u l t r a s o n i c radiation and of n o r m a l h e a r i n g the s t a t e m e n t is m i s l e a d i n g and such h e a r i n g would p r o b a b l y be exceptional. The s e c t i o n on coupling m a t e r i a l s again gives the i m p r e s s ion that many of t h e s e have an a c o u s t i c i m p e d a n c e midway between the t r a n s d u c e r and the s p e c i m e n w h e r e a s , when coupling to m e t a l s , none in g e n e r a l use has this value. The fact that all couplants a r e a c o m p r o m i s e could be made m o r e c l e a r . In s o m e p l a c e s a p a r t i c u l a r i l l u s t r a t i o n could be taken to i l l u s t r a t e a g e n e r a l principle, such a s that the echo f r o m p o r o s i t y in a weld defect will a p p e a r on the time b a s e b e f o r e that f r o m slag. The i l l u s t r a t i o n should have b e e n explained in m o r e detail o r a s i m p l e r i l l u s t r a t i o n chosen. The section on checking t r a n s d u c e r c h a r a c t e r i s t i c s is well up to date and v e r y useful, having so far a p p e a r e d mainly in r e p o r t s with l i m i t e d circulation. The book e n d s with a f u r t h e r c o m p a r i s o n of d i f f e r e n t techniques indicating with i l l u s t r a t i o n s w h e r e u l t r a s o n i c s may b e s t be used.
MAGNETIC PARTICLE TESTING
The l a s t of the u l t r a s o n i c p r o g r a m m e d i n s t r u c t i o n h a n d books r e i t e r a t e s the t y p e s of u l t r a s o n i c i n s p e c t i o n s y s t e m which can be u s e d and d e a l s with the r e l a t i v e a d v a n t a g e s and d i s a d v a n t a g e s of contact s c a n n i n g and i m m e r s i o n . S p e c i m e n s for which u l t r a s o n i c i n s p e c t i o n is unsuitable a r e shown and the r e a s o n s a r e explained. A useful, table g i v e s the f r e quency r a n g e s which m a y be u s e d f o r d i f f e r e n t t y p e s of m a t e r i a l s but the use of the l o w e r c a s e ' m ' for the p r e f i x ' m e g a ' a p p e a r s again. A m i n o r i r r i t a t i o n is the m i x t u r e of singular and plural, ie ' t h i s p h e n o m e n a o c c u r s only when sound b e a m s p a s s f r o m one m e d i a to a n o t h e r ' , in an o t h e r wise good d e s c r i p t i o n of the e f f e c t s of m a t e r i a l g r a i n s i z e .
A p p r o x i m a t e l y half of the p r o g r a m m e d i n s t r u c t i o n handbook on m a g n e t i c p a r t i c l e t e s t i n g i s c o n c e r n e d with m a g n e t i c t h e o r y although it i s c o m p l e t e l y n o n - m a t h e m a t i c a l . It p r o g r e s s e s in e a s y s t a g e s through field p a t t e r n s in v a r i o u s s h a p e s of m a g n e t i c m a t e r i a l s to the d i s t o r t i o n s c a u s e d by d e f e c t s in m a g n e t i c s p e c i m e n s and the p o s i t i o n s w h e r e m a g n e t i c p a r t i c l e s would collect. T h i s c o n c e n t r a t i o n on the qualitative explanation of m a g n e t i c t h e o r y is well worthwhile a s the c o r r e c t i n t e r p r e t a t i o n of i n d i c a t i o n s in r e a l s p e c i m e n s m u s t depend upon the o p e r a t o r ' s ability to v i s u a l i s e the d i r e c t i o n fields will take. F i e l d s around c o n d u c t o r s a r e also well explained, a s a r e the d i s t r i b u t i o n s of ac and dc fields within b a r s and tubes. The c a u s e s of i r r e l e v a n t i n d i c a t i o n s a r e c l e a r l y explained, the explanations following n a t u r a l l y f r o m the p r e v i o u s theory. The a p p e a r a n c e of d e f e c t s using v a r i o u s types of magnetic p a r t i c l e a r e once again shown c l e a r l y by m e a n s of well s e l e c t e d p h o t o g r a p h s of defective s p e c i m e n s . The B/H c u r v e is explained c l e a r l y in s t a g e s through the book, culminating in the final section on d e m a g n e t i s a t i o n .
A useful s e c t i o n g i v e s t a b l e s and g r a p h s f r o m which it i s p o s s i b l e to calculate the c o r r e c t wedge a n g l e s to g e n e r a t e d i f f e r e n t types of wave in v a r i o u s m a t e r i a l s . A c o m p r e h e n s i v e s e c t i o n d e a l s with weld i n s p e c t i o n and the v a r i o u s a i d s available for locating d e f e c t s within the weld when using manual i n s p e c t i o n t e c h n i q u e s . The use of high f r e q u e n c y t r a n s d u c e r s in i m m e r s i o n t e s t i n g i s well c o v e r e d t o g e t h e r with m e a n s for d e t e r m i n i n g flaw p o s i t i o n s by i n t e r r u p t i o n and anguiation of the incident b e a m . D e t a i l e d a p p l i c a t i o n s follow, m o s t l y c o n c e r n e d with w e l d s in plate and tube, although spot weld i n s p e c t i o n and d e t e c t i o n of flaws in bonded s t r u c t u r e s a r e included,
The m a g n e t i c p a r t i c l e c l a s s r o o m t r a i n i n g handbook b e g i n s with a s h o r t e r s e c t i o n on m a g n e t i c t h e o r y but n e v e r t h e l e s s c o v e r s a w i d e r field, still without involving anything but the s i m p l e s t m a t h e m a t i c s . M o r e attention is paid to the m a g n e tic m e d i a and thei~ p r e p a r a t i o n t o g e t h e r with the r e a s o n s the d i f f e r e n t t y p e s a r e u s e d in p a r t i c u l a r c a s e s . M e a n s of p r e s e r v i n g and r e c o r d i n g the i n d i c a t i o n s a r e d i s c u s s e d and all m e t h o d s a r e c o v e r e d . In condensing this book f r o m the p r e v i o u s one, the s e c t i o n on n o n - r e l e v a n t indications has all but d i s a p p e a r e d , which is a pity, a s an I n s p e c t o r who finds n o n - e x i s t e n t d e f e c t s i s a l m o s t a s much trouble a s one who fails to find s o m e of the r e a l ones.
All m a n n e r of f a l s e indications a r e shown and the ways to d i s t i n g u i s h t h e m explained. A point i s made, which i s often lost sight of, i s that a l a r g e t r a n s d u c e r will have a s m a l l e r b e a m angle and h e n c e may give b e t t e r r e s o l u t i o n at a d i s tance than a s m a l l e r one. The d e s c r i p t i o n of r e s o n a n c e t e c h n i q u e s is m o s t thorough, but one is a little s u r p r i s e d to s e e the point m a d e at this stage in the book that t h e r e is no
The final p a r t of this book once again r e p e a t s the e x c e l l e n t p h o t o g r a p h s of d e f e c t s and c o m p a r i s o n of techniques which a l r e a d y a p p e a r in the o t h e r c l a s s r o o m t r a i n i n g handbooks. Although it would involve m o r e work it would be b e t t e r if each of t h e s e s e c t i o n s c o n c e n t r a t e d on d e f e c t s d e t e c t a b l e by the method d e s c r i b e d in the book and i l l u s t r a t e d them by p i c t u r e s of indications given by this t e s t method.
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n o n - d e s t r u c t i v e t e s t i n g F e b r u a r y 1970
EDDY CURRENT TESTING Eddy c u r r e n t t e s t i n g i s c o v e r e d in two p r o g r a m m e d i n s t r u c tion handbooks. Half of the f i r s t book i s devoted to a gentle i n t r o d u c t i o n to the u n d e r l y i n g t h e o r y of the g e n e r a t i o n of eddy c u r r e n t s in s p e c i m e n s using e n c i r c l i n g coil, i n s i d e coil and s u r f a c e coil m e t h o d s , d e f e c t s h a r d l y b e i n g m e n t i o n e d , Once again, the t r e a t m e n t i s a l m o s t e n t i r e l y nonm a t h e m a t i c a l but is v e r y t h o r o u g h and should b e e a s i l y u n d e r standable_. The r e a d e r i s i n t r o d u c e d to a l l the v a r i a b l e s in m a t e r i a l s which c a n a f f e c t i n d i c a t i o n s and to the s p u r i o u s i n d i c a t i o n s due to ' l i f t off' v a r i a t i o n s and lack of p r o p e r c e n t e r i n g , although t h e r e is s o m e confusion between fill f a c t o r and c e n t e r i n g , The second half of the book i s devoted to a v e r y r e a d a b l e d e s c r i p t i o n of ac t h e o r y a s it a p p l i e s to eddy c u r r e n t testing. Some m a t h e m a t i c a l t r e a t m e n t i s i n e v i t a b l e but it is kept to a m i n i m u m and at e a c h stage the a p p l i c a t i o n of the t h e o r y to a p r a c t i c a l p r o b l e m h e l p s to r e t a i n the s t u d e n t ' s i n t e r e s t . T h i s i s not an e a s y s u b j e c t to t e a c h without p r e v i o u s g r o u n d w o r k and t h i s e f f o r t i s v e r y c r e d i t a b l e . It is h a r d to b e l i e v e that anyone who could follow this book would need the type of i n t r o d u c t i o n to ndt c o n t a i n e d in t h e s e v o l u m e s .
c o n c i s e f o r m and at the s a m e t i m e goes m o r e deeply into the subject. There is an interesting section on conductivity showing how t h i s i s g o v e r n e d by the a t o m i c and m o l e c u l a r s t r u c t u r e of an e l e m e n t or alloy and how t h i s s t r u c t u r e i s a l t e r e d b y h e a t t r e a t m e n t , cold working i etc. M o r e a t t e n t i o n i s paid to p r a c t i c a l s y s t e m s and e x a m p l e s a r e given of p r o b l e m s and how t h e s e a r e b e s t solved. A s with all the c l a s s r o o m t r a i n i n g handbooks, useful c h a r t s and g r a p h s a r e given which would n e e d to b e r e f e r r e d to by an I n s p e c t o r e n gaged in eddy c u r r e n t testing. The s e c t i o n c o v e r i n g the s e l e c t i o n of t e c h n i q u e s for p a r t i c u l a r p r o b l e m s again a p p e a r s in t h i s handbook, p r e s u m a b l y on the a s s u m p t i o n that books c o v e r i n g only one s u b j e c t m a y be p u r c h a s e d i n s t e a d of the c o m p l e t e set.
SUMMARY The books c o v e r i n g r a d i o g r a p h i c i n s p e c t i o n w e r e u n f o r t u n a t e l y l o s t in the p o s t but p e r h a p s t h e s e can be r e v i e w e d at a l a t e r date.
The next book d e a l s in m o r e detail with the d i f f e r e n t types of coil which can b e u s e d and e x p l a i n s the v a r i o u s d i s p l a y s which can d i s t i n g u i s h b e t w e e n p e r m e a b i l i t y , d i m e n s i o n a l , and conductivity c h a n g e s in the s p e c i m e n . The e x p l a n a t i o n s a r e c l e a r and thorough. The m e t h o d s of s e t t i n g s t a n d a r d s a r e d i s c u s s e d and a useful t a b l e of c o n d u c t i v i t i e s of d i f f e r e n t m e t a l s and al]~ys is given in the s e c t i o n dealing with the s o r t i n g of m a t e r i a l s by eddy c u r r e n t m e a n s . The l a t t e r p a r t of the book goes into m o r e d e t a i l of the a p p l i c a t i o n s of diff e r e n t coils to a p p r o p r i a t e s p e c i m e n s and shows how f a l s e i n d i c a t i o n s can be avoided o r how the r e q u i r e d s i g n a l m a y b e o b t a i n e d f r o m a m o n g s t f a l s e i n d i c a t i o n s . T h e book ends with a g r a p h enabling one to choose the c o r r e c t f r e q u e n c y to obtain a d e s i r e d p e n e t r a t i o n with v a r i o u s d i f f e r e n t materials,
To s u m up, t h e s e v o l u m e s contain a good collection of worthwhile p r a c t i c a l i n f o r m a t i o n b a c k e d up by v e r y good i l l u s t r a t i o n s . The f o r m in which s o m e of it i s p r e s e n t e d would indicate t h a t it i s a i m e d a t an i n t e l l i g e n c e which is below that u s u a l l y c o n s i d e r e d n e c e s s a r y in an I n s p e c t o r and it c e r t a i n l y a s s u m e s no p r e v i o u s knowledge of any of the s u b j e c t s . It should b e s t r e s s e d t h a t the a p p r o a c h i s s t r i c t l y p r a c t i c a l and the c o u r s e would t u r n out an I n s p e c t o r capable of s t a r t i n g work in the ndt field with an adequate u n d e r s t a n d i n g of what he i s doing, but no depth of knowledge. The c h a t t y a p p r o a c h i s p r o b a b l y m o r e a c c e p t a b l e in the USA than in this country; it i s c e r t a i n l y s u r p r i s i n g to s e e the a n s w e r to a question in a t e c h n i c a l book b e g i n n i n g 'Yep, t h a t ' s r i g h t ' and 'NO ? ? ? Holy Cow !'. Only the c l a s s r o o m t r a i n i n g handbooks could b e c o n s i d e r e d a s r e f e r e n c e books and the o t h e r s m u s t be r e a d a s a c o u r s e of i n s t r u c t i o n .
The c l a s s r o o m t r a i n i n g handbook, a s m i g h t b e expected, c o v e r s a l l the ground of the o t h e r two books, but in m o r e
D. Dean
LETTER TO THE EDITOR Crack depth d e t e r m i n ~ i o n With r e f e r e n c e to NON-DESTRUCTIVE TESTING, Vol 2, No 3 (August 1969) p131, we u n d e r s t a n d f r o m your e d i t o r i a l , e s p e c i a l l y p a r a g r a p h 5, t h a t in your opinion c r a c k depth d e t e r m i n a t i o n i s s t i l l l a r g e l y u n r e s o l v e d . With t h i s we e m p h a t i c a l l y d i s a g r e e a s f a r a s c r a c k s in i r o n and s t e e l a r e concerned. You r e c e i v e d a s h o r t while ago a p a p e r by o u r D r D e u t s c h d e s c r i b i n g e x t e n s i v e l y the p o s s i b i l i t i e s of exact c r a c k depth m e a s u r e m e n t . The c o n t e n t s of t h i s p a p e r w e r e b a s e d on a r e p o r t given by D r D e u t s c h d u r i n g the m e e t i n g at Keele of the N o n - D e s t r u c t i v e T e s t i n g Society of G r e a t B r i t a i n .
The method u s e d by u s h a s b e e n developed to a high l e v e l of p e r f o r m a n c e and the c r a c k depth m e a s u r i n g i n s t r u m e n t s m a d e by u s a r e working to the full s a t i s f a c t i o n of all o u r c l i e n t s in all p a r t s of the world. KARL DEUTSCH ( M a n u f a c t u r e r s of t e s t i n g and m e a s u r i n g equipment) 5600 Wuppertal 1, P o s t f a c h 3115, Germany. ( E d i t o r ' s note: D r D e u t s c h ' s p a p e r w a s r e c e i v e d in this office, but u n f o r t u n a t e l y i t s length p r o h i b i t e d p u b l i c a t i o n in t h i s journal)
ERRATUM N o n - d e s t r u c t i v e t e s t i n g of high p r e s s u r e g a s p i p e l i n e s R. F. L u m b , NON-DESTRUCTIVE TESTING, Vol 2, No 4 ( N o v e m b e r 1969) pp 259-268
p p p p it
259: Fig 1 is upside down. 260: F i g 3, s e c t i o n s b and c a r e upside down. 264: Fig 12, a r e f e r e n c e to R e f e r e n c e 18 i s omitted. 265: T a b l e 1, the r e f e r e n c e to Fig 12 is i n c o r r e c t , should b e Fig 13. n o n - d e s t r u c t i v e t e s t i n g F e b r u a r y 1970
61
Non-destructive testing h a n d b o o k s G e n e r a l D y n a m i c s , C o n v a i r Division, 1967 A s e t of ' p r o g r a m m e d i n s t r u c t i o n ' and ' c l a s s r o o m t r a i n i n g ' handbooks d e s i g n e d f o r the t r a i n i n g of ndt i n s p e c t o r s and o p e r a t o r s . T h e s e v o l u m e s c o v e r the following a s p e c t s of ndt p r a c t i c e : (1) I n t r o d u c t i o n (2) Eddy c u r r e n t t e s t i n g (3) M a g n e t i c p a r t i c l e t e s t i n g (4) U l t r a s o n i c t e s t i n g (5)
Liquid p e n e t r a n t t e s t i n g
INTRODUCTION One is s u r p r i s e d when f i r s t opening the i n t r o d u c t o r y book to find the left h a n d p a g e s p r i n t e d u p s i d e down. T h i s i s not a p r i n t e r ' s e r r o r , but i s p a r t of the t e a c h i n g technique i n c o r p o r a t e d in the book. At e a c h s t a g e the r e a d e r i s p o s e d q u e s t i o n s and a s a r e s u l t of h i s a n s w e r i s r e f e r r e d to a new page in the book w h e r e t h i s p a r t i c u l a r a n s w e r i s d i s c u s s e d , If the a n s w e r i s not c o r r e c t the r e a d e r i s s e n t to c h o o s e another, The book then goes on to show how a l l d e f e c t s can be c a t e g o r i s e d a s d i s c o n t i n u i t i e s and g i v e s s o m e v e r y obvious e x a m p l e s of t h e s e in the f o r m of q u e s t i o n s which could only be a n s w e r e d i n c o r r e c t l y by a m o r o n . The next s e c t i o n c o n t a i n s a d e s c r i p t i o n of the s t e e l - m a k i n g p r o c e s s and shows c l e a r l y how i n c l u s i o n s , p o r o s i t y a n d pipe o c c u r . T h i s o c c u p i e s 27 p a g e s but could h a v e b e e n c o n d e n s e d into f a r fewer,
The f i r s t book s t a r t s by s t r e s s i n g that only d e f e c t s r e a c h i n g the s u r f a c e can be d e t e c t e d by t h i s m e t h o d and e x p l a i n s the i m p o r t a n c e and m e t h o d s of cleaning. A w a r n i n g i s given about the toxic and i n f l a m m a b l e n a t u r e of s o m e c l e a n i n g fluids and of the r i s k of closing d e f e c t s by shot b l a s t i n g . The q u a l i t i e s r e q u i r e d of a dye p e n e t r a n t a r e d i s c u s s e d and the c l a s s i f i c a t i o n into f l u o r e s c e n t and n o r m a l l y v i s i b l e dyes i s explained. The use of b l a c k light is mentioned, but t h i s i s s a i d to b e a h a r m l e s s r a d i a t i o n b e t w e e n the v i s i b l e and the u l t r a - v i o l e t . Since the two a r e a d j a c e n t in the s p e c t r u m t h i s n e e d s a m p l i f i c a t i o n , and a w a r n i n g should be given of the p o s s i b l e d a n g e r s of e x c e s s i v e e x p o s u r e to u l t r a - v i o l e t r a d i a t i o n if adequate f i l t r a t i o n i s not used. T h e r e follows the next step of application, and w a r n i n g s a r e given about allowing sufficient dwell t i m e and using the p e n e t r a n t b e t w e e n fixed t e m p e r a t u r e l i m i t s . R e m o v a l of e x c e s s p e n e t r a n t i s c o v e r e d in c o n s i d e r a b l e d e t a i l and c a r e ful d i s t i n c t i o n i s m a d e between the m e t h o d s u s e d for d i f f e r ent types of p e n e t r a n t . The c o r r e c t u s a g e of both wet and d r y d e v e l o p e r s i s dealt with v e r y well and w a r n i n g s a r e given of the p i t f a l l s which m a y be e n c o u n t e r e d . T h e final s t e p s of i n s p e c t i o n and cleaning a r e a c c o m p a n i e d by a c l e a r s e l e c t i o n of i l l u s t r a t i o n s showing the a p p e a r a n c e of p e n e t r a n t in v a r i o u s t y p e s of defect. The a d v a n t a g e s of u s i n g m a g n e t i c and f i l t e r e d p a r t i c l e t e s t s a r e then explained followed by a long s e c t i o n which is p a r t i a l l y a r e c a p i t u l a t i o n and p a r t i a l l y an e x e r c i s e in applying what h a s b e e n l e a r n e d to a c t u a l p r o b l e m s . The final p a r t of the book shows typical i n s p e c t i o n s e t - u p s and d e s c r i b e s s p e c i a l p e n e t r a n t s which m u s t b e u s e d when c o m p a t i b i l i t y is a p r o b l e m . The C l a s s r o o m T r a i n i n g Handbook on liquid p e n e t r a n t t e s t i n g I found to b e laid out in a m a n n e r m u c h m o r e to m y liking and to contain c o n s i d e r a b l y m o r e d e t a i l e d i n f o r m a t i o n .
The next page c o n t a i n s four s e c t i o n s e a c h with a w o r d m i s s ing o r p a r t i a l l y m i s s i n g and an a r r o w pointing o v e r l e a f , The f i r s t i n c o m p l e t e s t a t e m e n t i s ' T h e r e a r e - arrows on t h i s e n t i r e page (write in the c o r r e c t numl~er of a r r o w s ) ' Comment is superfluous, If one i s not put off by the n a i v e t y of s o m e of what h a s gone b e f o r e and r e a d s on, a useful section follows in which the n a t u r e of d e f e c t s in b a r stock and p l a t e i s e x p l a i n e d and the r e a d e r i s shown how t h e s e o r i g i n a t e f r o m the d e f e c t s in b l o o m s to b e c o m e s e a m s , s t r i n g e r s , etc. P r o b a b l y the b e s t s e c t i o n in the book c o n c e r n s forging and c a s t i n g p r o c e s s e s and the d e f e c t s which a r e likeIy to occur, with c l e a r e x p l a n a t i o n s of the f o r m a t i o n of laps, b u r s t s , hot t e a r s and cold s h u t s . T h e r e a r e a m p l e c l e a r i l l u s t r a t i o n s of all t h e s e conditions. A f t e r i n v e r t i n g the book, one r e a d s b a c k t h r o u g h pages c o n c e r n e d with f u r t h e r types of c a s t i n g defects, The f o r m a t i o n of s l u g s and d e f e c t s in w e l d s in tubing i s explained, followed by e x t r u s i o n d e f e c t s and g r i n d i n g cracks, D e f e c t s due to h e a t t r e a t m e n t a r e m e n t i o n e d and explosive f o r m i n g and the r e s u l t a n t d e f e c t s a r e also c o v e r e d . E x a m p l e s a r e quoted of the i m p o r t a n c e of s t r e s s r a i s e r s in i n i t i a t ing d e f e c t s . The final s e c t i o n d e a l s c l e a r l y with the f o r m a tion of c o m m o n d e f e c t s in w e l d s b a c k e d up by adequate illustrations.
A f t e r an i n t r o d u c t i o n giving t e s t i n g philosophy the g e n e r a l p r i n c i p l e s a r e e x p l a i n e d in a c o n c i s e m a n n e r , i l l u s t r a t e d by c h a r t s of the v a r i o u s p r o c e s s e s . The following two c h a p t e r s list the e q u i p m e n t and m a t e r i a l s r e q u i r e d a n d d e s c r i b e the t e c h n i q u e s for u s i n g t h e m . A useful table i s i n c l u d e d giving t i m e s for v a r i o u s p a r t s of the p r o c e s s e s to d e t e c t a wide v a r i e t y o~ flaws in m a n y d i f f e r e n t m a t e r i a l s . W a r n i n g s of f a l s e i n d i c a t i o n s a r e c o n t a i n e d in the c h a p t e r on i n t e r p r e t a t i o n of r e s u l t s and this is c l e a r l y i l l u s t r a t e d with p h o t o g r a p h s of defective p a r t s . The f o r m a t i o n of c r a c k s in a r t i f i c i a l t e s t b l o c k s is d e s c r i b e d in the section on quality c o n t r o l of p e n e t r a n t s , e m u l s i f i e r s and d e v e l o p e r s . The book c o n c l u d e s with a s e c t i o n which i s m o s t valuable, but would s e e m b e t t e r s u i t e d to a g e n e r a l book on t e s t i n g since it c o m p a r e s the e f f e c t i v e n e s s of d i f f e r e n t ndt techniques for each type of defect. I do not think anyone could q u a r r e l s e r i o u s l y with the r e c o m m e n d a t i o n s and once a g a i n it is v e r y e f f e c t i v e l y i l l u s t r a t e d with e x a m p l e s of defective p a r t s which m u s t have taken a long t i m e to collect. T h i s s e c t i o n should be r e a d by any ndt p r a c t i t i o n e r who i s i n c l i n e d to be p a r t i s a n about his f a v o u r i t e technique.
The addition of i n s t r u c t i o n in how d e f e c t s a r e f o r m e d to an ndt c o u r s e i s well w o r t h w h i l e and should i n c r e a s e the value of an I n s p e c t o r who m a y b e able to a s s i s t with the e l i m i n a tion of d e f e c t s a s well a s t h e i r detection,
T h e f i r s t volume c o v e r i n g u l t r a s o n i c t e s t i n g i s e n t i t l e d ' B a s i c P r i n c i p l e s ' and i n t r o d u c e s the r e a d e r to the s u b j e c t via the m e d i a of a s e r i e s of b a l l s i m p a c t i n g upon each o t h e r in t u r n and v i b r a t i o n of p l a t e s s t r u c k with a h a m m e r . The c o n c e p t s of a cycle of oscillation, f r e q u e n c y and p e r i o d a r e c l e a r l y explained. T r a n s m i s s i o n of sound through v a r i o u s m e d i a i s then c o v e r e d , but the p r o b l e m s of a n a i r b a r r i e r a r e not too c l e a r l y e x p l a i n e d and one could f o r m the i m p r e s s i o n that the change of v e l o c i t y was the main p r o b l e m . The s t a t e m e n t that ' a i r does not do a v e r y good job of t r a n s m i t t i n g sound' i s d e m o n s t r a b l y u n t r u e and m o r e could have b e e n made of the i n t e r f a c e p r o b l e m .
LIQUID P E N E T R A N T TESTING Liquid p e n e t r a n t t e s t i n g i s c o v e r e d in two handbooks, the f i r s t a p r o g r a m m e d i n s t r u c t i o n book s i m i l a r in style to the i n t r o d u c t o r y book, and the o t h e r i n t e n d e d for c l a s s r o o m training,
ULTRASONIC TESTING
n o n - d e s t r u c t i v e t e s t i n g F e b r u a r y 1970
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A b r i e f d e s c r i p t i o n of a t r a n s d u c e r , its b e a m d i v e r g e n c e , the n e a r and f a r z o n e s and the m e a n i n g of wavelength a r e all adequately c o v e r e d . The d e s c r i p t i o n g i v e s the i m p r e s s i o n that attenuation in signal o c c u r s only in the far zone, but this may not be intended. The r e a d e r i s then i n t r o d u c e d gradually to the laws g o v e r n i n g p r o p a g a t i o n of u l t r a s o u n d in m a t e r i a l s and a c r o s s i n t e r f a c e s and v e r y c l e a r e x p i a n a t i o n s a r e given of the d i f f e r e n t types of wave and how they a r e g e n e r a t e d . It i s s u r p r i s i n g that although the d e p e n d e n c e of t r a n s m i s s i o n a c r o s s an i n t e r f a c e on a c o u s t i c a l i m p e d a n c e is mentioned, the f o r m u l a is not given in the s a m e way a s most others, The book e n d s with explanations of p u l s e r e f l e c t i o n , through t r a n s m i s s i o n and r e s o n a n c e t e s t i n g and points out the p r o b l e m s of p o o r s u r f a c e coupling and s o m e of the ways in which s p u r i o u s e c h o e s can occur. The g e n e r a l layout of [he book i s s i m i l a r to the i n t r o d u c t o r y volume including the self-testing sections, The second p r o g r a m m e d handbook on u l t r a s o n i c t e s t i n g b e gins with a d e t a i l e d introduction to the d i f f e r e n t types of u l t r a s o n i c contact t r a n s d u c e r s and e x p l a i n s how they a r e coupled to s p e c i m e n s . P o s s i b l y a m i s p r i n t i s the use of the lower c a s e ' m ' f o r the p r e f i x ' m e g a ' and this will no doubt be c o r r e c t e d in l a t e r editions, The use of v a r i o u s t y p e s of l e n s e s f o r b e a m shaping and defect r e s o l u t i o n i s well explained but the s t a t e m e n t that ' a c o l l i m a t o r a d d e d to the f r o n t of a t r a n s d u c e r r e d u c e s the b e a m s p r e a d and p r o d u c e s a s m a l l e r and s t r a i g h t e r sound b e a m ' is not c o r r e c t , s i n c e the b e a m s p r e a d following a b e a m limiting a p e r t u r e m u s t be g r e a t e r than f r o m a l a r g e r t r a n s d u c e r face. Wheel and b u b b l e r t r a n s d u c e r s a r e a l s o c o v e r e d . The s e c t i o n on coupling m a t e r i a l s can a l s o be m i s leading s i n c e although the s t a t e m e n t that a coupling fluid should be midway in a c o u s t i c i m p e d a n c e b e t w e e n the t r a n s d u c e r and s p e c i m e n i s n e a r l y enough c o r r e c t , it i s not made plain that this condition is h a r d l y e v e r a p p r o a c h e d in practice. V a r i o u s d i f f e r e n t t e s t blocks a r e c o v e r e d and w a r n i n g s a r e given of the d i f f e r e n c e s between e c h o e s f r o m r e a l and a r t i f i c i a l d e f e c t s . The r e s t of the book d e s c r i b e s v e r y adequately the d i f f e r e n t c o n t r o l s on an u l t r a s o n i c t e s t set and how they should be used. All t y p e s of equipment a r e v e r y fully c o v e r e d a s is the p r e s e n t a t i o n of i n f o r m a t i o n on a facsimile plotter,
radiation h a z a r d . The implication could be drawn that this h a z a r d e x i s t s with o t h e r f o r m s of u l t r a s o n i c inspection. At each a p p r o p r i a t e point in the book the use and c o n s t r u c t i o n of a p p r o p r i a t e t e s t blocks is always included. The u l t r a s o n i c c l a s s r o o m training handbook, a s with the o t h e r books of this type, c o n c e n t r a t e s the contents of the p r o g r a m m e d i n s t r u c t i o n handbooks into a f o r m which this r e v i e w e r finds m o r e a c c e p t a b l e . It also t a k e s m a t t e r s f u r t h e r and adds additional useful m a t e r i a l . It would s e e m that s o m e of the i n t r o d u c t o r y p a r a g r a p h s have been s h o r t e n ed in a m a n n e r leading to s t a t e m e n t s which could e a s i l y be m i s i n t e r p r e t e d . A s an example, the s t a t e m e n t is made that ' N o r m a l adults may h e a r n o t e s of f r e q u e n c i e s higher than 16, 000 c y c l e s p e r s e c o n d (16 Kc) - - up to about 20,000 c y c l e s p e r second (20 Kc)'. Without additional definition of the l i m i t s of u l t r a s o n i c radiation and of n o r m a l h e a r i n g the s t a t e m e n t is m i s l e a d i n g and such h e a r i n g would p r o b a b l y be exceptional. The s e c t i o n on coupling m a t e r i a l s again gives the i m p r e s s ion that many of t h e s e have an a c o u s t i c i m p e d a n c e midway between the t r a n s d u c e r and the s p e c i m e n w h e r e a s , when coupling to m e t a l s , none in g e n e r a l use has this value. The fact that all couplants a r e a c o m p r o m i s e could be made m o r e c l e a r . In s o m e p l a c e s a p a r t i c u l a r i l l u s t r a t i o n could be taken to i l l u s t r a t e a g e n e r a l principle, such a s that the echo f r o m p o r o s i t y in a weld defect will a p p e a r on the time b a s e b e f o r e that f r o m slag. The i l l u s t r a t i o n should have b e e n explained in m o r e detail o r a s i m p l e r i l l u s t r a t i o n chosen. The section on checking t r a n s d u c e r c h a r a c t e r i s t i c s is well up to date and v e r y useful, having so far a p p e a r e d mainly in r e p o r t s with l i m i t e d circulation. The book e n d s with a f u r t h e r c o m p a r i s o n of d i f f e r e n t techniques indicating with i l l u s t r a t i o n s w h e r e u l t r a s o n i c s may b e s t be used.
MAGNETIC PARTICLE TESTING
The l a s t of the u l t r a s o n i c p r o g r a m m e d i n s t r u c t i o n h a n d books r e i t e r a t e s the t y p e s of u l t r a s o n i c i n s p e c t i o n s y s t e m which can be u s e d and d e a l s with the r e l a t i v e a d v a n t a g e s and d i s a d v a n t a g e s of contact s c a n n i n g and i m m e r s i o n . S p e c i m e n s for which u l t r a s o n i c i n s p e c t i o n is unsuitable a r e shown and the r e a s o n s a r e explained. A useful, table g i v e s the f r e quency r a n g e s which m a y be u s e d f o r d i f f e r e n t t y p e s of m a t e r i a l s but the use of the l o w e r c a s e ' m ' for the p r e f i x ' m e g a ' a p p e a r s again. A m i n o r i r r i t a t i o n is the m i x t u r e of singular and plural, ie ' t h i s p h e n o m e n a o c c u r s only when sound b e a m s p a s s f r o m one m e d i a to a n o t h e r ' , in an o t h e r wise good d e s c r i p t i o n of the e f f e c t s of m a t e r i a l g r a i n s i z e .
A p p r o x i m a t e l y half of the p r o g r a m m e d i n s t r u c t i o n handbook on m a g n e t i c p a r t i c l e t e s t i n g i s c o n c e r n e d with m a g n e t i c t h e o r y although it i s c o m p l e t e l y n o n - m a t h e m a t i c a l . It p r o g r e s s e s in e a s y s t a g e s through field p a t t e r n s in v a r i o u s s h a p e s of m a g n e t i c m a t e r i a l s to the d i s t o r t i o n s c a u s e d by d e f e c t s in m a g n e t i c s p e c i m e n s and the p o s i t i o n s w h e r e m a g n e t i c p a r t i c l e s would collect. T h i s c o n c e n t r a t i o n on the qualitative explanation of m a g n e t i c t h e o r y is well worthwhile a s the c o r r e c t i n t e r p r e t a t i o n of i n d i c a t i o n s in r e a l s p e c i m e n s m u s t depend upon the o p e r a t o r ' s ability to v i s u a l i s e the d i r e c t i o n fields will take. F i e l d s around c o n d u c t o r s a r e also well explained, a s a r e the d i s t r i b u t i o n s of ac and dc fields within b a r s and tubes. The c a u s e s of i r r e l e v a n t i n d i c a t i o n s a r e c l e a r l y explained, the explanations following n a t u r a l l y f r o m the p r e v i o u s theory. The a p p e a r a n c e of d e f e c t s using v a r i o u s types of magnetic p a r t i c l e a r e once again shown c l e a r l y by m e a n s of well s e l e c t e d p h o t o g r a p h s of defective s p e c i m e n s . The B/H c u r v e is explained c l e a r l y in s t a g e s through the book, culminating in the final section on d e m a g n e t i s a t i o n .
A useful s e c t i o n g i v e s t a b l e s and g r a p h s f r o m which it i s p o s s i b l e to calculate the c o r r e c t wedge a n g l e s to g e n e r a t e d i f f e r e n t types of wave in v a r i o u s m a t e r i a l s . A c o m p r e h e n s i v e s e c t i o n d e a l s with weld i n s p e c t i o n and the v a r i o u s a i d s available for locating d e f e c t s within the weld when using manual i n s p e c t i o n t e c h n i q u e s . The use of high f r e q u e n c y t r a n s d u c e r s in i m m e r s i o n t e s t i n g i s well c o v e r e d t o g e t h e r with m e a n s for d e t e r m i n i n g flaw p o s i t i o n s by i n t e r r u p t i o n and anguiation of the incident b e a m . D e t a i l e d a p p l i c a t i o n s follow, m o s t l y c o n c e r n e d with w e l d s in plate and tube, although spot weld i n s p e c t i o n and d e t e c t i o n of flaws in bonded s t r u c t u r e s a r e included,
The m a g n e t i c p a r t i c l e c l a s s r o o m t r a i n i n g handbook b e g i n s with a s h o r t e r s e c t i o n on m a g n e t i c t h e o r y but n e v e r t h e l e s s c o v e r s a w i d e r field, still without involving anything but the s i m p l e s t m a t h e m a t i c s . M o r e attention is paid to the m a g n e tic m e d i a and thei~ p r e p a r a t i o n t o g e t h e r with the r e a s o n s the d i f f e r e n t t y p e s a r e u s e d in p a r t i c u l a r c a s e s . M e a n s of p r e s e r v i n g and r e c o r d i n g the i n d i c a t i o n s a r e d i s c u s s e d and all m e t h o d s a r e c o v e r e d . In condensing this book f r o m the p r e v i o u s one, the s e c t i o n on n o n - r e l e v a n t indications has all but d i s a p p e a r e d , which is a pity, a s an I n s p e c t o r who finds n o n - e x i s t e n t d e f e c t s i s a l m o s t a s much trouble a s one who fails to find s o m e of the r e a l ones.
All m a n n e r of f a l s e indications a r e shown and the ways to d i s t i n g u i s h t h e m explained. A point i s made, which i s often lost sight of, i s that a l a r g e t r a n s d u c e r will have a s m a l l e r b e a m angle and h e n c e may give b e t t e r r e s o l u t i o n at a d i s tance than a s m a l l e r one. The d e s c r i p t i o n of r e s o n a n c e t e c h n i q u e s is m o s t thorough, but one is a little s u r p r i s e d to s e e the point m a d e at this stage in the book that t h e r e is no
The final p a r t of this book once again r e p e a t s the e x c e l l e n t p h o t o g r a p h s of d e f e c t s and c o m p a r i s o n of techniques which a l r e a d y a p p e a r in the o t h e r c l a s s r o o m t r a i n i n g handbooks. Although it would involve m o r e work it would be b e t t e r if each of t h e s e s e c t i o n s c o n c e n t r a t e d on d e f e c t s d e t e c t a b l e by the method d e s c r i b e d in the book and i l l u s t r a t e d them by p i c t u r e s of indications given by this t e s t method.
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n o n - d e s t r u c t i v e t e s t i n g F e b r u a r y 1970
EDDY CURRENT TESTING Eddy c u r r e n t t e s t i n g i s c o v e r e d in two p r o g r a m m e d i n s t r u c tion handbooks. Half of the f i r s t book i s devoted to a gentle i n t r o d u c t i o n to the u n d e r l y i n g t h e o r y of the g e n e r a t i o n of eddy c u r r e n t s in s p e c i m e n s using e n c i r c l i n g coil, i n s i d e coil and s u r f a c e coil m e t h o d s , d e f e c t s h a r d l y b e i n g m e n t i o n e d , Once again, the t r e a t m e n t i s a l m o s t e n t i r e l y nonm a t h e m a t i c a l but is v e r y t h o r o u g h and should b e e a s i l y u n d e r standable_. The r e a d e r i s i n t r o d u c e d to a l l the v a r i a b l e s in m a t e r i a l s which c a n a f f e c t i n d i c a t i o n s and to the s p u r i o u s i n d i c a t i o n s due to ' l i f t off' v a r i a t i o n s and lack of p r o p e r c e n t e r i n g , although t h e r e is s o m e confusion between fill f a c t o r and c e n t e r i n g , The second half of the book i s devoted to a v e r y r e a d a b l e d e s c r i p t i o n of ac t h e o r y a s it a p p l i e s to eddy c u r r e n t testing. Some m a t h e m a t i c a l t r e a t m e n t i s i n e v i t a b l e but it is kept to a m i n i m u m and at e a c h stage the a p p l i c a t i o n of the t h e o r y to a p r a c t i c a l p r o b l e m h e l p s to r e t a i n the s t u d e n t ' s i n t e r e s t . T h i s i s not an e a s y s u b j e c t to t e a c h without p r e v i o u s g r o u n d w o r k and t h i s e f f o r t i s v e r y c r e d i t a b l e . It is h a r d to b e l i e v e that anyone who could follow this book would need the type of i n t r o d u c t i o n to ndt c o n t a i n e d in t h e s e v o l u m e s .
c o n c i s e f o r m and at the s a m e t i m e goes m o r e deeply into the subject. There is an interesting section on conductivity showing how t h i s i s g o v e r n e d by the a t o m i c and m o l e c u l a r s t r u c t u r e of an e l e m e n t or alloy and how t h i s s t r u c t u r e i s a l t e r e d b y h e a t t r e a t m e n t , cold working i etc. M o r e a t t e n t i o n i s paid to p r a c t i c a l s y s t e m s and e x a m p l e s a r e given of p r o b l e m s and how t h e s e a r e b e s t solved. A s with all the c l a s s r o o m t r a i n i n g handbooks, useful c h a r t s and g r a p h s a r e given which would n e e d to b e r e f e r r e d to by an I n s p e c t o r e n gaged in eddy c u r r e n t testing. The s e c t i o n c o v e r i n g the s e l e c t i o n of t e c h n i q u e s for p a r t i c u l a r p r o b l e m s again a p p e a r s in t h i s handbook, p r e s u m a b l y on the a s s u m p t i o n that books c o v e r i n g only one s u b j e c t m a y be p u r c h a s e d i n s t e a d of the c o m p l e t e set.
SUMMARY The books c o v e r i n g r a d i o g r a p h i c i n s p e c t i o n w e r e u n f o r t u n a t e l y l o s t in the p o s t but p e r h a p s t h e s e can be r e v i e w e d at a l a t e r date.
The next book d e a l s in m o r e detail with the d i f f e r e n t types of coil which can b e u s e d and e x p l a i n s the v a r i o u s d i s p l a y s which can d i s t i n g u i s h b e t w e e n p e r m e a b i l i t y , d i m e n s i o n a l , and conductivity c h a n g e s in the s p e c i m e n . The e x p l a n a t i o n s a r e c l e a r and thorough. The m e t h o d s of s e t t i n g s t a n d a r d s a r e d i s c u s s e d and a useful t a b l e of c o n d u c t i v i t i e s of d i f f e r e n t m e t a l s and al]~ys is given in the s e c t i o n dealing with the s o r t i n g of m a t e r i a l s by eddy c u r r e n t m e a n s . The l a t t e r p a r t of the book goes into m o r e d e t a i l of the a p p l i c a t i o n s of diff e r e n t coils to a p p r o p r i a t e s p e c i m e n s and shows how f a l s e i n d i c a t i o n s can be avoided o r how the r e q u i r e d s i g n a l m a y b e o b t a i n e d f r o m a m o n g s t f a l s e i n d i c a t i o n s . T h e book ends with a g r a p h enabling one to choose the c o r r e c t f r e q u e n c y to obtain a d e s i r e d p e n e t r a t i o n with v a r i o u s d i f f e r e n t materials,
To s u m up, t h e s e v o l u m e s contain a good collection of worthwhile p r a c t i c a l i n f o r m a t i o n b a c k e d up by v e r y good i l l u s t r a t i o n s . The f o r m in which s o m e of it i s p r e s e n t e d would indicate t h a t it i s a i m e d a t an i n t e l l i g e n c e which is below that u s u a l l y c o n s i d e r e d n e c e s s a r y in an I n s p e c t o r and it c e r t a i n l y a s s u m e s no p r e v i o u s knowledge of any of the s u b j e c t s . It should b e s t r e s s e d t h a t the a p p r o a c h i s s t r i c t l y p r a c t i c a l and the c o u r s e would t u r n out an I n s p e c t o r capable of s t a r t i n g work in the ndt field with an adequate u n d e r s t a n d i n g of what he i s doing, but no depth of knowledge. The c h a t t y a p p r o a c h i s p r o b a b l y m o r e a c c e p t a b l e in the USA than in this country; it i s c e r t a i n l y s u r p r i s i n g to s e e the a n s w e r to a question in a t e c h n i c a l book b e g i n n i n g 'Yep, t h a t ' s r i g h t ' and 'NO ? ? ? Holy Cow !'. Only the c l a s s r o o m t r a i n i n g handbooks could b e c o n s i d e r e d a s r e f e r e n c e books and the o t h e r s m u s t be r e a d a s a c o u r s e of i n s t r u c t i o n .
The c l a s s r o o m t r a i n i n g handbook, a s m i g h t b e expected, c o v e r s a l l the ground of the o t h e r two books, but in m o r e
D. Dean
LETTER TO THE EDITOR Crack depth d e t e r m i n ~ i o n With r e f e r e n c e to NON-DESTRUCTIVE TESTING, Vol 2, No 3 (August 1969) p131, we u n d e r s t a n d f r o m your e d i t o r i a l , e s p e c i a l l y p a r a g r a p h 5, t h a t in your opinion c r a c k depth d e t e r m i n a t i o n i s s t i l l l a r g e l y u n r e s o l v e d . With t h i s we e m p h a t i c a l l y d i s a g r e e a s f a r a s c r a c k s in i r o n and s t e e l a r e concerned. You r e c e i v e d a s h o r t while ago a p a p e r by o u r D r D e u t s c h d e s c r i b i n g e x t e n s i v e l y the p o s s i b i l i t i e s of exact c r a c k depth m e a s u r e m e n t . The c o n t e n t s of t h i s p a p e r w e r e b a s e d on a r e p o r t given by D r D e u t s c h d u r i n g the m e e t i n g at Keele of the N o n - D e s t r u c t i v e T e s t i n g Society of G r e a t B r i t a i n .
The method u s e d by u s h a s b e e n developed to a high l e v e l of p e r f o r m a n c e and the c r a c k depth m e a s u r i n g i n s t r u m e n t s m a d e by u s a r e working to the full s a t i s f a c t i o n of all o u r c l i e n t s in all p a r t s of the world. KARL DEUTSCH ( M a n u f a c t u r e r s of t e s t i n g and m e a s u r i n g equipment) 5600 Wuppertal 1, P o s t f a c h 3115, Germany. ( E d i t o r ' s note: D r D e u t s c h ' s p a p e r w a s r e c e i v e d in this office, but u n f o r t u n a t e l y i t s length p r o h i b i t e d p u b l i c a t i o n in t h i s journal)
ERRATUM N o n - d e s t r u c t i v e t e s t i n g of high p r e s s u r e g a s p i p e l i n e s R. F. L u m b , NON-DESTRUCTIVE TESTING, Vol 2, No 4 ( N o v e m b e r 1969) pp 259-268
p p p p it
259: Fig 1 is upside down. 260: F i g 3, s e c t i o n s b and c a r e upside down. 264: Fig 12, a r e f e r e n c e to R e f e r e n c e 18 i s omitted. 265: T a b l e 1, the r e f e r e n c e to Fig 12 is i n c o r r e c t , should b e Fig 13. n o n - d e s t r u c t i v e t e s t i n g F e b r u a r y 1970
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