Plastic coupon

The weep point or strain-to-first-crack in a wall for filament-wound pipe constructed using isophthalic plastic is currently found to be not less than 0.009 in./in. This has been repeatedly demonstrated by careful coupon testing and burst testing of pipes with strain gauge instrumentation attached. 

ASTM D2688 provides a standard test method for measuring the corrosivity of water via weight loss coupons. And the fact is that unless a suitable protocol such as ASTM D2688 is employed for coupon preparation, installation, and subsequent cleaning, variable rates of corrosion are often obtained. Even when protocols are strictly enforced, some variation is usually found, and therefore it is common practice to employ several coupons at the same time, employing a steel or plastic bypass test rack. 

Coupon corrosion results are also influenced by the mounting and installation process within a bypass unit. Coupons must be mounted with plastic, or other suitable nonconducting, holders to ensure insulation from stray currents and electrolytic effects. The plane of the coupon should be parallel to the direction of flow and it should not touch the wall of the pipe. 

Install blank coupons made of plastic to determine the degree of fouling that the metal coupons will undergo. 

Steel, copper, and most other metal coupons should be cleaned by washing under running water and brushing to remove any loose deposits. If oily, first wash with acetone/isopropanol (IPA). Further clean by immersion in concentrated HCl for 15 seconds. Treat again with HCl and brushing or use of a plastic knife, if necessary, to remove tenacious deposits. Dip in acetone, then IPA, and finally dry in a desiccator prior to weighing. 

Fig. 1 shows the force-distance plots for the carbon, (a), and the glass, (b) laminates with a notch depth of 5mm (for all samples except (p = 15° glass, which had 4mm notches). It can be seen that the (p = 15° and 30° laminates were stressed to failure without any significant plasticity effects being evident. The 45° coupons, on the other hand, had much quasi-stable deformation before failure, while the 60° and 75° laminates broke very easily. 

This limited number of coupons, coupled with apparent variations in the plastic film process variables such as non-uniformity of orientation, coating thicknesses, results in property data scatter. When a small number of truly promising materials have been Isolated, large numbers of coupons should be tested, providing sufficient data for statistical treatment. 

Specific creep tests have not been developed for composites at the coupon level. Data have been obtained using several of the standard test geometries described above, but creep is normally considered less of a problem than fatigue. The creep tests for plastics. ISO 899 [31], can be used for guidance with the standard composite specimens. 

The corrosion coupons are 31.75 mm diameter discs 3.175 mm thick and with a hole in the centre to fit over an insulated stainless steel rod. Plastic insulators separate individual coupons. The coupons are not preoxidized at elevated temperature in water but have the normal air formed oxide. This condition should make them more sensitive to any water chemistry changes. Four basic types of corrosion coupon are being tested in the L basin and RBOF water environments ... 

The widespread application of fiberglass-reinforced plastic (FRP) composites has prompted comparative testing for resistance to bleaching solutions [107], Coupons were prepared in accordance with ASTM C 581 (Practice for Determining Chemical Resistance of Thermosetting Resins Used in Glass Fiber-Reinforced Structures Intended for Liquid... 

Screws and nuts made of nylon or plastic shonld be nsed to hold the coupons to the conpx>n holder. Mixed metallurgy should be avoided. Coppier-base screws and nuts should not be used to hold carbon steel or stainless steel coupx>ns. Galvanized screws and nuts should never be used. 

Too high a fiow rate will keep debris off of the coupons and may initiate erosion attack on copp>er-base alloys. Low fiow rates may result in excessive corrosion and fouling. Normally, fiow rates of 1-2 m/s (3 to 5 ft/s) are adequate. The coupx)n rack should be connected to the return riser to the tower or at the exit of the hottest part of the system using plastic piping or any other material that will not influence coupmn corrosion rates. For example, do not use galvanized pip>e, coppjer pip e, or brass v Jves to connect the... 

The standards are published in both collective book form and in separate pamphlet form. The Annual Book of AS TM Standards is published yearly in 47 volumes called Parts , Standards can be located by subject or number from the Content Listings in the front of each book. Of interest are Parts 34 and 36, which deal with plastics, and Part 48, the index of all standards. Prices of each part vary. At present Parts 34,35,36, and 48 sell for 18.00, 31.00, 24.00 and 4.00, respectively. Individual standards in lots less than 50 may be purchased by coupon only. A five-coupon book is available at 6.00 and a 25-coupon book at 30.00. Orders should be directed to ASTM, 1916 Race Street, Philadelphia, PA 19103. 

RTR pipe designers also use a S-S curve but instead of a yield point, they use the point of first crack (empirical weep point). Either the ASTM hydrostatic or coupon test determines it. The weep point is the point at which the RTR matrix (plastic) becomes excessively strained so that minute fractures begin to appear in the structural wall. At this point it is probable that in time even a more elastic liner on the inner wall will be damaged and allow water or other liquid to weep through the wall. Even with this situation, as is the case with the yield point of steel pipe, reaching the weep point is not catastrophic. It will continue to withstand additional load before it reaches the point of ultimate strain and failure. By using a more substantial, stronger liner the weep point will be extended on the S-S curve. 

Figure 9.32 Metal coupons in a plastic test rack exposed at the Kennedy Space Center beach corrosion test site besides a CLIMAT coupon. (Courtesy of Battelle)...

A cell consisting of a hollow plastic cylinder is quite adequate for this test. The test coupon can be inserted between the hollow cylinder and the solid base, which also serves as the bottom of the cell (Fig. 7.9). A... 

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