3.5 Lines and Valves

The following are recommended engineering practices for ethylbenzene:

• lines smaller than 25 mm in diameter should not be used,
• a minimum of flanged connections is preferred because of leak potential,
• lines should not be buried because of the difficulty of checking for leakage,
• all lines should be sloped so they can be completely drained for maintenance,
• newly installed lines should be pressure tested by an approved method before insulation.

Thermal expansion in blocked ethylbenzene lines which are exposed to the sun without relief protection can cause high pressure, which can result in failure of gaskets, pump seals, and pump housings. If burial is preferred, the regulatory requirements to protect soil and ground water should be observed. A dip pipe should extend to the bottom of the tank and be provided with a pinch hole (siphon break). The electrical continuity across connections should be checked to ensure grounding. Lines constructed of carbon steel are acceptable, but copper, bronze, or plastic should not be used. Large lines are usually joined by welded flanges, while for smaller lines threaded joints are satisfactory. Ethylbenzene can dissolve pipe dope and thus cause product colouration and contamination. To avoid this, the pipe threads can be wrapped with PTFE [poly(per)tetrafluoroethylene] tape.

As with all transport equipment, caution should be taken with the choice of valve. All valves should be protected against climatic extremes, shock and mechanical stress. A fusible airline or equally effective safety shutoff valve should be installed to close off lines in case of excessive external heat. Emergency block valves for isolation of equipment by remote activation may be considered on storage tanks, unloading stations and long pipelines holding large amounts of ethylbenzene. Plug cocks and ball valves, lined with fluoro-elastomer, give excellent service with stainless steel balls. Gate valves are less satisfactory, but usually cheaper, and may be used. Lubricated plug cocks and non-lubricated ball-type valves are satisfactory. The piping system should use either ball valves or plug valves. Gate valves may be considered for applications with infrequent use. The piping system should use plug valves rather than ball-valves for all manually and infrequently operated valves. To limit emissions from packed glands, bellow valves may be considered. Drain line valves should be provided with a cap or end-flange. Valves must be protected against freezing, heat shock, or mechanical stress.

Details on material compatibility with ethylbenzene are found in Appendix 3.

CEFIC
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Patrick Detournay
T +32 2 676 72 05
E pdt@cefic.be