Drawing shows some of the methods available for detecting microscopic leaks in equipment. Unshaded portion is the tank's jacket, which is filled with the medium used in the test. W i t h method 7 , for e x a m p l e , the jacket is filled with ammonia. W h e n the ammonia seeps through the microscopic leak, it shows up as a purple streak when it comes in contact with the bromocresol purple reagent brushed on the interior o f the tank. W i t h method 3, helium would be used in the jacket of the tank. AMMONIA
RADIOACTIVE PHOSPHATE
1.
Halide Leak Detector
Fairly sensitive, m o d e r a t e cost, takes f a i r amount o f time 2.
Halide Torch
- MCTHYlEMf R4.UE, FLUOKESGBN, OR OTHERS
Easy t o use, questionable f o r microscopic leaks, inexpensive 3.
H e l i u m M a s i Spectrometer
G o o d sensitivity, m a y b e t o o b u l k y f o r some j o b s , f a i r l y expensive, but can b e rented 4.
Infrared Leak Detector
C a n b e a u t o m a t e d , f a i r l y e x p e n s i v e , easy t o use, g o o d sensitivity 5.
Sensitivity lems 6.
l i m i t e d , contamination
prob
Radioactive Tracer Methods
Expensive, s a f e t y consuming 7.
NITROUS OXIDE
Dye Penetration
precautions a r e
time
Bromocresol Purple
G o o d sensitivity, inexpensive, use, safe
easy
to
How to Find Microscopic Leaks in Process Equipment b y PHILIP WINTER, H. R. BILFORD, CARL E. JACOB, and R. A. KEMMERER Bristol Laboratories, Inc., Syracuse, Ν. Υ.
W h a t ' s the best way to find microscopic leaks in process equipment? Confronted with the actual problem, and the need to find a n d eliminate the leak quickly a n d eco nomically, the engineer has at his disposal a n u m b e r of different methods. Some m a y be suitable and capable of doing the j o b quickly. O t h e r methods m a y not be applicable in the same case. In our plant, we developed leaks—too tiny to be de tected by ordinary methods—in two large production fermentcrs, one equipped with interior cooling coils and the other with a jacket for cooling. T h e problem was serious because contaminants, chiefly bacterial, were coming from the cooling water and playing havoc with production. r W h e n several of the plant personnel got together to discuss how we should go about finding
these leaks, there was a variety of ideas, but little agree ment. I n a p p r o a c h i n g this particular problem, we considered both new and established methods. Some of our experi ences in the search for a method that would work best for us are outlined here. Some other methods or equip m e n t might work better in solving your microscopic leak detection problem. Using at least one of the methods described here, however, you will be off to a good start. T h e general problem of sh yellow by the presence of a halide gas. If the coils or jacket of equipment is filled with a mixture of Freon gas and air, leaks can be detected by exploring the outside area with the torch
Can be used to locate leaks that are too tiny for detection with soapy water. Sensitivity is reported to be about 20 parts of refrigerant gas per million parts of air. Open flame may be a disadvantage
Helium Mass ^nortmmptpr "
Sorts out elements according to relative mass weights and counts the number of atoms present. Helium mass spectrometer is designed to detect helium, the leak-detecting agent
Leaks on the order of 10 - 1 0 cc. per second can be detected. The instrument is being used in connection with certain equipment for atomic energy work and the handling of liquid oxygen. The unit is portable, although somewhat bulkier than the halide leak detector. It is also equipped with a suction hose and funnel through which air is drawn. Presence of helium is indicated by a warning signal system. In locating leaks in jacketed vessels, fill jacket with helium or air-helium mixture. Then check interior tank surface for leak; or, fill jacket with helium or air-helium mixture and apply vacuum to tank proper. Check vacuum exhaust for presence of helium (indicates presence of leak, but does not define area of leak) ; or, maintain jacket under high vacuum while bombarding localized interior areas with helium gas stream. While doing this, check vacuum exhaust from jacket for presence of helium.
Involves induction of nitrous oxide into a closed system and detection of its presence *^ e g a s e s c a P e s I r o m t n e system
Sensitivity is stated to be one part nitrous oxide in 1 to 20 million parts of air. A leak of 3 X 10 _ s cc. per second can be detected under certain sample flow conditions. By manually moving a probe over the nitrous oxide pressurized system, the operator is given both visible and audible indication of a leak. Variations in loudspeaker pitch and meter reading lead to location of leak point. The new instrument is used by automobile manufacturers to test air suspension systems before units are applied to cars.
Infrared Leak Detector
as
S p o t Checking and Dye Penetrants
Methylene Blue. A deeply penetrating and readily available dye. In our tests, we used a water solution of about 0.4 pound per 100 gallons of water. A disadvantage is its limited sensitivity. Fluorescein. A sharply penetrating dye which fluoresces vividly under ultraviolet light. We plahned to add this dye under pressure to the jacket and after a waiting period, examine the interior of the tank under ultraviolet light. However, even though tank interior areas appear shiny and clean under normal light, inspection under ultraviolet light revealed extensive fluorescence. This precluded the possibility of using fluorescein. Zyglo leak detector is marketed by Magnaflux Corp. The leak shows up as a visible fluorescent spot or line under black light, as shown in photograph ât right. Commercial Spot Leak Checkers. Leak-Tec is a formula marketed by American Gas & Chemicals, Inc., New York, Ν. Υ. When spread over the surface to be tested, the compound forms a white foam and live bubbles at the area of the leak. It is furnished in handy polyethylene bottles.—Turco Products, Los Angeles, Calif., markets a product called Dy-Chek for location of flaws in metal structures. Turco's system involves (1) thorough cleaning of the metal surface, (2) applying Dy-Chek penetrant, (3) removing surface penetrant with Dy-Chek remover-emulsifier, (4) drying the area, (5) applying Dy-Chek developer by spray, and (6) interpreting results. Red indications appear at the location of the defects. Ritter Chemical Co., Amsterdam, N. Y., has a similar product called Chex-All. The surface is prepared as above, and penetrant sprayed or brushed on the surface. After about 10 minutes the penetrant is wiped off and the Chex-AU developer is sprayed on the area. Defects show upon drying developer. One gallon of penetrant covers up to 3000 square feet. Spotcheck is a dye penetrant developed by Magnaflux Corp.
Radioactive Tracer
The most applicable and readily available tracer material is probably radioactive phosphorus, P 32 . The minimum amount required to help find the leak in our tanks was calculated to be 37.85 curies, but ten times that amount might have been necessary to ensure a successful test. For some applications, cost may make use of the material prohibitive. Tracers Expensive auxiliary equip a r e m o r e o r i e s s difficult to obtain and long delays are involved in the procedure required. ment is needed and lengthy methods are involved in disposal of radioactive material. Test operations require safety precautions beyond the scope of practicability at most plants.
Methods
Chemical Reactions
Various chemical reactions may be used as sensitive indicators of leaks in process equipment. reactions: S0 2 + 2NH 3 + H 2 0 - * (NHi) 2 S0 3 (white mist)
» Bromocresol PurDle ,. J? , Method
54 A
Here are several such (1)
Pb(Ac) 2 + H 2 S
—
PbS + 2HAc
(2)
2AgN0 3 + H 2 S
—
Ag2S + 2HNÛ3
(3)
Ammonia gas reacts with bromocresol purple in solution at just below pH 5.0, with the ammonia gas changing the color of ' **ye s o n j t ' o n from a light yellowish green to vivid purple Our requirements for the solution were: 1. It must adhere well to the tank wall when applied with a brush. 2. It must react promptly to give a purple color with ammonia. 3. It must be readily and completely removable at conclusion of tests. Here is our recipe : Take 40 mg. of bromocresol purple and dissolve in 4 ml. of 0.02iV sodium hydroxide. Dilute to 100 ml. In a separate container, add 10 grams of starch to 500 ml. of boiling water. Stir to form a slurry. Add the dye solution to the starch slurry. To this mixture, add 5 ml. of Tween 40 wetting agent. Adjust pH to 5.0 with dilute hydrochloric acid. To test, put a small portion of the indicating agent on a small piece of paper and move the paper rapidly
t le
INDUSTRIAL AND ENGINEERING CHEMISTRY
Process Equipment Cost About $750
Supply Sources General Electric Co. Beckman Instruments, Inc. Veeco Vacuum Corp.
If Prest-O-Lite soldering torch available, only Any refrigeration or air-conditioning equipextra tip is needed, about $7. Cost of com- ment supply house plete unit, about $70
General Electric halide leak detector showing probe and control unit
$3500 to $4500. Equipment may be leased Beckman Instruments, Inc. under special arrangements Veeco Vacuum Corp. General Electric Co. Consolidated Electrodynamics Corp
$4500
Perkin-Elmer Corp. Beckman Instruments, Inc.
Methylene Blue Nominal Any scientific supply house Fluorescein Nominal Any scientific supply house Zyglo Nominal Magnaflux Corp. Leak-Tec Recent introductory cost $15 per case of twelve 4-ounce bottles American Gas & Chemicals, Inc. Dy-Chek Turco Products Per gallon in 5-gallon cans about $5 Per gallon in 55-gallon drums $2.30 Chex-All Ritter Chemical Co. Spot check, complete kit $36 Magnaflux Corp.
About $1000 per curie
Beckman helium mass spectrometer, showing some details of inside construction
Beckman infrared t y p e leak detector. This detector uses nitrous oxide
LEAK TIC
camsmxni
In 1, when the two gases come into contact with each other in the presence of a small amount of moisture, a white mist occurs. Both gases are hazardous and care must be exercised in their use. In Reactions 2 and 3, the black sulfides form at the site of the leak. Most of the reactions we looked at were found to be impractical in view of the type of reaction involved or the danger of introducing toxic elements in microscopic amounts, the positive removal of which might prove difficult later. through the air, horizontally about 12 inches away from an open top of a bottle of standard ammonia reagent. Immediate appearance of purplish color on paper shows agent is ready for trial application. Otherwise, slight additional pH adjustment may be necessary. Our application procedure was : The tank jacket was drained and dried, then filled with ammonia gas under 43 p.s.i. and allowed to stand overnight. The adjusted bromocresol solution was applied section by section with a brush to the interior tank wall. The method is time-consuming, but safe, and the cost is low. As interior of the tank wall was being checked, the indicator reagent suddenly turned purple along a 3-foot horizontal section of a weld seam near center of tank wall. Repair of the seam eliminated the leak. A product based on the bromocresol purple principle is available from Chemical Products Corp., Seattle 88, Wash.
Leak detector in a squeeze bottle
Zyglo leak detector shows up as fluorescent spot or line under black light VOL. 50, NO. 5
·
MAY 1958
55 A
