Spark testing

Before an item of equipment lined with ebonite or any soft rubber leaves the workshop it is tested for non-porosity. According to regular practice, the only reliable method of determining this is that which makes use of a spark tester or inductor and a test voltage of 20,000 to 25,000 volts. For this purpose the spark tester or the inductor has been proved successful. 

The following guide should be used while inspecting and spark testing of rubber lined tanks. 

The probe shape is very important. The wand should be L shaped, measuring 12 on both sides of the L. This will allow coverage of 12 per pass with the wand. The wire diameter should be approximately 3/32 , with a 1/2 radius at the bend. Also, the tip should be turned up to eliminate the end discharge. On the intricate parts of the configuration, a fan probe is recommended, similar to a snare drum brush. Care should be exercised not to stop and concentrate on any one area. The wand should be passed over the rubber in a continuous sweeping stroke, approximately 10 inches per second. 

It is imperative to proportion the spark voltage settings to the thickness of the lining to be tested. The following range of voltage is recommended as a starting point for calibration  

Materials such as neoprene and graphite loaded linings require even lower voltage ranges 7,500 volts for 1/8 and 3/16 , and 

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In enamels for chemical plant such as autoclaves it is not only the degree of acid resistance which is important but also the freedom of the finish from minute flaws detectable by high frequency spark testing or chemical methods. The chemical methods depend upon a colour change when the reagent such as ammonium thiocyanate reacts with the iron exposed at the bottom of the pinhole or flaw in the finish. Alternatively, an electric cell can be formed via the exposed iron in the flaw and detected chemically. 

Holiday detection or spark testing may be specified in the contract with details of the appropriate instrument and testing procedure. In certain cases. 

ECTFE (60,90) adhesive Full vacuum up to 120°F Spark Testing recommended... 

Dispersion and up to 80 mils when multicoat Vacuum ok Spark Testing... 

Bottles and vials are not subjected to such a vacuum test because of the flexibility of the rubber closure. However, bottles that are sealed under vacuum may be tested for vacuum by striking the base of the bottle sharply with the heel of the hand to produce a water hammer sound. Another test is the spark test, in which a probe is applied outside the bottle. When it reaches the air space of the bottle, a spark discharge occurs if the headspace is evacuated. 

The most practical tests specifically followed for rubber lining are hardness test, spark test and immersion test. Hardness test is invariably the most frequently prescribed test for rubber lining quality by clients, though it is an inadequate test. The term hardness is a vague one the different expressions such as "Scratch Hardness","Cutting Hardness" "Abrasion Hardness" etc. illustrate that different concepts of hardness exist. 

Spark testing should be performed by qualified persons with a high frequency... 

An alternative method is to use high-voltage spark testing (500 V to 30 kV) either in the DC or the AC mode. There are several methods for carrying out these tests, shown here. 

Steel Structure Paint Council white metal blast surface preparation Proposed test method for pinhole detection by high-voltage spark testing by DC... 

Different values for the minimum ignition energy are obtained in low voltage circuits with an ohmic (R) and inductive (L) load. As a switching element, a spark test apparatus with counter-rotating tungsten wires and a cadmium... 

Part 3 Spark test apparatus for intrinsically safe circuits... 

Table 6.38 Reference gas-air mixtures to be used in the spark test apparatus (at T = 293 K and p = 1.013 105Pa)...

So, in a research project, PTB Physikalisch-Technische Bundesanstalt, Germany, has investigated the influence of real cables on spark ignition theoretically and in practical trials using the spark test apparatus. ... 

Spark test apparatus applied to intrinsically safe electrical circuits. 

The shafts shall be tightened when entering the explosion chamber (1). This chamber shall withstand an explosion pressure of 1.5 MPa (=15 bar). Figure 8.12 shows a longitudinal section drawing of the spark test apparatus and Fig. 8.13 this apparatus in its entirety (cover of explosion chamber removed, however). 

Due to its construction, there are some limitations for the spark test apparatus ... 

The spark test apparatus must not influence the circuit to be tested, e.g. the circuit inductance must not be increased by the apparatus inductance. So, the parameters of the apparatus are ... 

Figure 8.11 Spark test apparatus. Functional scheme. Dimensions are given in mm.

With this spark test apparatus, the reference curves (minimum ignition curves) of Figs 6.162 to 6.167 (showing price ratio ex-protected to non-ex-protected cage induction motors versus rated power types of protection -(E) Ex e IIT3 (E) Ex d IIC T4 and (E) Ex d IIB T4) have been established with reference gas-air mixtures according to Table 6.38. 

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