6.  SAFETY MEASURES IN EQUIPMENT DESIGN

Till now we have discussed about number of safety measures for preventing or controlling hazards. Some of these measures are significant in equipment design problems. Here main focus is on considering equipment such as pressure vessels (i.e. reactors, heat exchangers etc.) and the equipment which involves rotary motion (example filters, agitators etc.). During the design stages of these items of equipment some important safety measures need to be considered are discussed in the following sections.

6.1 About material of construction

The selection of materials certainly involves a compromise between factors such as strength, corrosion resistance, elasticity, toughness, wear, fatigue resistance and ease of fabrication, as well as availability and cost. In some cases process conditions vary a good deal, which makes the choice of material difficult. The choice of the material is largely based on experience and even small variations in the constituents of the fluid streams make considerable difference to the material to be used. At the design stage, all reasonable hazards should be identified and listed, and a limit set for each variable which can lead to such a hazard. For instance, the consequences of material failure or deterioration should be considered, with limits for wear or corrosion being established. To ensure safe operation a critical analysis of the process conditions and material handled must be made.

6.2 Precautions in design and construction

It is generally known that preventing the effects of industrial accidents/hazards necessitates, above all, a high safety standard of potentially dangerous plants. These will vary according to the type of equipment. A properly designed piece of equipment will have in-built safety and loss prevention features. To prevent such failures the ideas and experience which are already available at various points in connection with emergency measures should be incorporated. These might include, for example, unit reliability and flexibility, ease of operations, provision for future expansion, inspection and maintenance, emergency shutdown facility, standardization of equipment for rapid replacement, design to withstand probable pressure and temperature range, with facility to over pressure/temperature control etc. But at the same time it is not possible to give the list of precautions for each and individual unit operations, some are specified below.

6.3 Pressure vessels

For design and construction of pressure vessel and storage tanks Indian standards codes should be followed and vessels should be tested at 1.3 times the design pressure ( Mahajani and Umarji, 2009 ). The design should be made to keep the vessels as simple as possible and it should not be overloaded with supplementary equipments. Thick weld joints made on the vessel should be given special attentions. The fatigue strength should be regularly monitored particularly if the vessel is exposed to pressure cycling, system changes, vibrations or similar factors which are likely to create fatigue conditions. Important point need to consider is that flange joints must be leak proof. All pressure vessels should be provided with pressure relief devices.