Rubber Lining Testing

Unless test coupons are produced alongside the lining, the only method of testing the vulcanisation state is with a hand hardness meter. A Shore A or IRHD meter is used for soft rubber linings and a Shore D meter for ebonites. The usual specification is that the hardness has to conform to 5° of the specified hardness. There is no quantitative non-destructive test for the strength of the bond between the lining and the substrate and so such tests are usually carried out in the laboratory on a sample prepared from the materials used. 

Any leaks at the metal joints found during hydraulic testing should be repaired before the start of rubber lining and not during the operation. 

Pressure vessels and pipes should be subjected to hydraulic testing before rubber lining. 

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. 

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

Though a standard norm or absolute reference value is not available for comparison in any of the international standard specifications and the technical and research publications with respect to the chemical resistance properties of rubber, liquid immersion tests certainly provide relative and useful data with which the suitability of anticorrosive rubber lining compounds can be assessed with a fair degree of accuracy. For this reason manufacturers and applicators of rubber lining resort to tests under simulated conditions instead of accelerated ageing immersion or swelling tests. 

If temperatures are not specified in the specification, the immersion tests have to be carried out at room temperature. The volume of the immersion liquids should be adequate enough to immerse the sample of rubber. The test should be carried out in the absence of direct sunlight to avoid atmospheric oxidation. Test pieces from cut samples or counter samples from the finished rubber lining compound have to be buffed smooth. 

This glossary explains terms related to the manufacture, preparation, application and testing of rubber linings and allied materials... 

Test methods for determining chemical resistance of plastics Effects of liquids on rubbers, test method Test method for chemical resistance of protective linings Test method for determining chemical resistance of fiberglass-reinforced thermosetting resin... 

Chemical resistance test for rubber linings by Atlas blind flange test Determination of effects of liquid chemicals on plastics Determination of environmental stress cracking (ESC) by the bent strip method... 

The spark test equipment tests rubber linings for the presence of pin holes and it consists of a main or direct current (DC) operated generator or interrupter, to which a Tesla coil is added within a tuned circuit. The coil operates best at a fairly high frequency and is capable of generating a very high peak alternating current (AC) voltage. 

A number of specifications and codes of practice are followed throughout the world for rubber lining, the major ones being from the ASTM, the BS Specifications, the German Institute for Standardisation (DIN) and the Japanese Industrial Standards (JIS) which give exhaustive information on rubber lining procedures, testing methods and code of practice. 

ASTM D2240-05 [4] deals with the procedure for rubber lining and equipment. ASTM D429-03el [5] deals with adhesion to rigid substrates. The Annual Book of ASTM Standards Part 38 Section 09 [6, 7] is a useful reference for rubber products, industrial specifications and related test methods. 

The media filters shown in Figure 4.4 are rubber-lined (5 mm thick) carbon steel (ASME coded-stamped) vessels, 2.4 m diameter (D) X 1.83 m SSH and rated for a working pressure of 7 bar g. The hydraulic test pressure rating is 10 bar g. The internal distribution system consists of a PVC upper distribution system and a header and lateral bottom collection system. Each vessel is provided with two 8 cm X 30 cm sight glasses and a 40 cm X 50 cm elliptical man-way. All face piping is PVC, and accessories include pneumatic... 

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