Before I would include the rubber I would check if it is realy necessary. For instance we hade NB700 pipes with 12 mm WTH and 4 mm rubber, which has a dencity of 1.06. Pipe has seawater inside. I would not worry too much with the rubber. Mayby I ask our customer if they considered. Nuclear Power Station Cooling Water (safety class 2).
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Regards,
Jouko
jouko@jat.co.za