A new method for the detection of very small leaks in pipe systems

VACUUM Classified A b s t r a c t s Abstract No. ~ud Raerone~

I --

General

Science

and

Engineering

~

I

Contd.

permissible level in ~,c/cm a. T h e s e m a x i m u m permissible levels are given in a table, r e p r o d u c e d below. F r o m Maximum

P e r m i s s i b l e L e a k s i n A it*

Radiosco pa H a ~Na ~

KVa C r 51 Mn56 Xea~a po2t0

U (natural) pu2a~ Beta-gamma emitter (isotope unknown) Alpha emitter (isotope unknown)

3I P L

(lc/cm,)

2 × 1 0 "s 2 X 10-~ 2 >< 1 0 -s 8 × 1 0 "~ 4><, 1 0 -6 2 ~ 10 "n 7 × 10 -n 1.7 X 1 0 - n 2 :< 1 0 "l~ 1 X l 0 -~ 5 > : 1 0 "~'°

*Reproduced from Radiologieal Handbook, U.S. Dept. ltealth, Educatiou and Welfare (1954).

Article by J. P. Vorkarnp & S. L. Williams .¥ucleonic~

x4, Juno 1956 54-57

',3/I

Article by P. Niviere Gen. Chim.

75, May 1956 122-123

1 ~S

s u c h d a t a can be deduced, for e x a m p l e , t h a t a m a x i m u m leak r a t e for fission gases w i t h a m a x i m u m permissible level of 2 × 10 -e t~c/cm 3 (based on X e *aS) w o u l d be 2 × 104 t,c/hr, in a 107-ft 3 building. A n allowable l e a k r a t e of 10 -6 cma/sec, is conceivable. H e n c e , specialised t e c h n i q u e s are n e c e s s a r y for r a p i d detection. E x c e s s i v e l e a k a g e c a n p r o d u c e a direct r a d i a t i o n h a z a r d . A g r a p h is given s h o w i n g t h e dose r a t e t h a t m i g h t be e x p e c t e d f r o m leaks in a sodium-cooled p l a n t . T h e l e a k - t e s t i n g m e t h o d c h o s e n d e p e n d s on t h e t y p e of h e a t - t r a n s f e r fluid a n d m a t e r i a l of c o n s t r u c t i o n used. F o r p r e s s u r i s e d - w a t e r a n d l i q u i d - m e t a l s y s t e m s , s u m m a r i s e d d a t a is given c o m p a r ing t h e m a s s spectromer, t h e h a l o g e n sniffer, t h e soluble-dye test, a n d t h e u s e of radioisotopes. T h e m a s s spectrom e t e r is t h e m o s t sensitive t e c h n i q u e . T h e u n i t specially designed for l e a k - t e s t i n g i n d i c a t e s 1 p a r t of h e l i u m in 2 × 105 p a r t s of air a n d is t h u s capable of d e t e c t i n g a l e a k of a b o u t 2 × I0 -4 m c f h . To a t t a i n u l t i m a t e sensitivity, however, t h e surfaces to be t e s t e d m u s t be s c r u p u l o u s l y cleaned a n d e x t r e m e care is required. T h u s , in p r a c t i c a l field work, 0.005 m c f h is t h e limit. A progressive p r o c e d u r e m a k i n g u s e of several t e s t s is preferred. F i r s t a h y d r o s t a t i c t e s t w i t h w a t e r s h o u l d be u s e d for c o m p o n e n t s a n d s u b - a s s e m b l i e s , t h e n t h e s o a p - b u b b l e t e s t for t r a c i n g of large l e a k s in t h e a s s e m b l e d s y s t e m . A f t e r r e p a i r i n g l e a k s so found, a h y d r o s t a t i c w a t e r t e s t s h o u l d be p e r f o r m e d on h i g h p r e s s u r e s y s t e m s ; e x p o s u r e of t h e s y s t e m to 1.5 t i m e s t h e design p r e s s u r e m a y open u p a d d i t i o n a l leaks. F i n a l l y t h e h a l o g e n or h e l i u m sniffer or s t a n d a r d m a s s s p e c t r o m e r leak t e s t i n g s h o u l d be applied. D e t a i l s g i v e n of a case s t u d y of l e a k - t e s t i n g a n all-metal, leak-welded sodium-cooled p l a n t of several h u n d r e d cubic feet.

A N e w M e t h o d for t h e D e t e c t i o n of V e r y Small L e a k s in Pipe S y s t e m s F r a n c e . A m e t h o d is described for leak d e t e c t i o n in c o m p l i c a t e d piping s y s t e m s . As the>- occur, in particular, in refrigerating plant, o p e r a t e d b y c o n d e n s a t i o n of a m m o n i u m gas w i t h o u t a n y m o v i n g part. Such p l a n t consists in p a r t of o x y - a c e t y l e n e welded iron pipes in spiral s h a p e w h i c h m u s t be k e p t free of t h e m o s t m i n u t e leaks a n d porosities in order to m a i n t a i n efficiency over t h e years. T h e p r e v i o u s m e t h o d of t e s t i n g i n v o l v e d i m m e r s i o n in w a t e r a n d filling t h e s y s t e m w i t h air a t 40 kg/cnl 2. Small leaks giving o n l y one b u b b l e e v e r y few m i n u t e s are easily m i s s e d in t h i s m e t h o d . T h e n e w m e t h o d provides for t h e filling of t h e s y s t e m w i t h a c o m pressed a i r - a m m o n i u m gas m i x t u r e a t 40 k g / c m 2 a n d a p p l y i n g a p a s t e c o n t a i n i n g p h e n o l p h t h a l e i n to t h e o u t s i d e of t h e pipes. A n y leaks p r e s e n t c a u s e t h e p e n e t r a t i o n of a m m o n i a to t h e o u t s i d e a n d t h i s is i m m e d i a t e l y d e t e c t e d b y a red s t a i n a p p e a r i n g in t h e p a s t e d u e to t h e a m m o n i a r e a c t i o n w i t h t h e p h e n o l p h t a l e i n . T h e a c t u a l p a s t e u s e d is a m i x t u r e of b a r i u m s u l p h a t e a n d water, to w h i c h glycerine (about 1:2) a n d c o m m e r c i a l p h e u o l p h t h a l e i n solution (25 c.c. of 5 0 alcoholic solution for each k i l o g r a m of paste) is added. T h e a p p l i c a t i o n of t h e p a s t e is as e a s y as t h a t of paint.

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I m p r o v e m e n t s r.t. L e a k D e t e c t i n g A p p a r a t u s for Use w i t h E x h a u s t i n g M a c h i n e r y See A b s t r a c t No.: 74/I

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L e a k - T e s t i n g of T y p e - 3 4 7 Stainless Steel W e l d s See A b s t r a c t No.: 93/I

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Conditioning P l a n t for S t e a m Turbine L u b r i c a t i n g Oils See A b s t r a c t No.: 167/III

Vacuum Vol. V I

October, 1956