Materials of construction
Proper selection of construction materials for 2-EHN service is essential to ensure the integrity of the handling system and to maintain product quality. Although stainless steel tanks are always preferred, 2-EHN may be stored in mild steel tanks, provided they are kept free from water bottoms through regular maintenance.
Mild steel in general is a material that requires careful consideration for use in a 2-EHN handling system. 2-EHN, in the presence of water bottoms, can hydrolyze slowly to form nitric acid, which can increase the corrosion rate of mild steel. For this reason, stainless steel is the preferred material for storage of 2-EHN.
Galvanized steel, copper and copper bearing alloys are unsuitable for any 2-EHN service. Special care should be taken when selecting such items as pumps and valves, to ensure that no copper alloys (e.g. brass or bronze) are used in bearings or other internal components that may come in contact with the product.
Elastomers and gaskets
2-EHN is an excellent solvent which can degrade the performance of some seals and gaskets. Careful selection is therefore necessary.
Piping / Lines / Hoses
Â Use non-insulated mild steel or stainless steel (SS) piping.
Any steam or electrical tracing must be physically disconnected.
Wherever possible, dedicated lines for 2-EHN are to be preferred to avoid safety or environmental problems.
Experimental fire testing, run by Shell, of gantry-type pipe work filled with an additive containing approximately 70% of 2-EHN, showed that a pressure relief valve set at 10 bar was sufficient to relieve pressure caused by the self-heating accelerated decomposition of 2-EHN.Â The pressure relief valve should discharge to a safe location.
Â SS full-bore ball valves are preferable.
Traditional ball, gate and butterfly valves may also be used.
SS, cast iron and cast steel are all suitable materials.
Copper, Zinc and its alloys, aluminium and most plastics are inadequate or incompatible materials.