Chemical are transfer by pipeline and also by different types of containers. Their Safety aspects are stated below.
Pipelines are required to carry a variety of materials such as water, steam, air, oil, gas (inert or toxic, vapour or compressed), brine, solvent and other liquid and gaseous chemicals. From storage tanks to process vessels, from process vessels to product tanks and there to filling (loading) points, pipelines are required. They may be above ground, underground or as per requirement, Some 20 to 30% costing is estimated and pipelines and their fittings like flange, valves, gauges, nipples, glands, bends, elbows, plugs, reducers, joints, couplings, vents, drains etc. Pipe work may be of cast iron, mild steel, stainless steel, lead, copper, plastic i.e. PVC, PP. HDPE, rubber, canvas, glass, FRP, glass lined, rubber lined, Teflon coated, asbestos cement, ICC, stone, ceramic etc.
Criteria for Piping Installation:
Main factors are – Material of construction, design and layout, supports and clamps, welding or flange joints, packing and gaskets, valves and other fittings, easy approach for working platform and testing and maintenance.
Material of construction is selected depending on nature (corrosively, toxicity, flammability etc.), quantity weight, flow, pressure) and other parameters like temperature, viscosity, colour, expansion etc. Thickness of pipe, its quality, welding pattern, flanging are to be considered while selecting for high pressure and temperature. For extremely hazardous chemicals, pipes are tested for inter granular corrosion and certified before used. Insulation is applied to preserve heat and tracing (contact tubing) for supplying heat to the inner material.
Various code like Indian Standards (hundreds of Indian Standards are prescribed for variety of pipes, their fittings, threads, colour code etc, see BIS handbook), ASME (American Code), British Standard (e.g BS 1710, 1319, 537, 4159) and International Standard ISO R 508 for colours for pipes for inland installations and on board ship, Indian Boiler Regulations also provide details for pipe selection, design, fabrication and testing for boiler purposes.
Safety Aspects of Pipe work:
Generally probability of leakage pipelines is proportional to the length of pipelines, number of joints, valves, vents, bleeds, drains etc. and complexity such as number of pump connections, recycle streams, hours of working etc. Therefore it is advisable to-
- Minimise pipe length, branches and joints, and flanges on vacuum lines.
- Provide welding joints for highly flammable or toxic chemical, good gaskets and gland packing flange guard to deflect leak downward, flexibility to allow thermal expansion, bellows subjected to axial movement, drains and traps at visible places, removable plugs on sample points, adequate pipe support, walkways, platforms or working place, proper slopping for draining, overhead clearance for vehicle movement (about 6 m), ergonomic design for valves to be operated and gauges to be seen, earthing and bounding to remove static charge due to flow, overflow return from measuring vessel to a storage tanks, painting with colour coding (IS:2379) and cathodic protection where required.
More pipe work in dyke is not desirable particularly with hazardous chemical, as it may be trapped in fire in the dyke. Similarly pipelines of flammable or toxic chemical should not be laid in tunnel, as its leak may spread from one area to another area. Electric cables or hot lines and flammable gas or liquid lines should not run side by side. Solvent line should not be laid below the corrosive line. Seam joints of rubber lined pipes should be kept upward.
Piping arrangement should be such that in case of failure at any point, the system can be quickly isolated by closing valves, without disturbing the rest of the system. Flushing arrangement should be provided for easy start up and maintenance. Pipe alleys should not run over the walking alleys, normal layout should be near the walls or in sides. To allow for thermal expansion special joints or loops should be provided.
Emergency control valves should be easily accessible. By-pass valves should be within easy reach.
Auto control valve should have bypass or manual valve which may be required in the event of failure of auto control valves. Particularly at the outlet of bulk storage of hazardous chemicals, manual and remotely controlled auto isolation valve both should be provided as near as possible to the outlet. Pressure relief device, liquid seal, manual vent etc. should be provided to depressurise the system where necessary.
Many different type of valve exist. It is essential to choose the type best suited for the particul operation it has to perform. For instance, if ball valves are to be fitted in a high pressure position, they should be trunnion mounted. Where positive segregation of products is required, say at a multi-product manifold, it is essential to provide block and bleed valves for continuous monitoring of valve seats and seals, For positive isolation some form of soft seat with a wedge gate action is desirable.
Pumps must be designed not only to suit the immediate pipeline requirements, but should take into account future development. Thus, it may be necessary to stipulate a pump casing pressure much higher than the pump can generate, if series or boosting pumping is envisaged. Care should be taken to insure that additional or larger impellers can be fitted as the system demand grows. The maximum operating pressure for the pump mechanical seals should match the pump capabilities. It may be necessary to provide product filtration to protect the minimum clearance of the pump moving parts, particularly on modern high efficiency pumps.
Flexible pipes, joints and hoses should be safe, sound and properly tested. Bolted clips are preferred to jubilee clips. Proper supports or hangers are necessary.
Glass piping, equipment or gauge needs external protection to protect against external impact or internal bursting and flying fragments coming out.
Layout drawing of piping and fittings should be maintained and corrected when any changes are incorporated.
Use of plastic piping is increasing. When it is used for hazardous gas like hydrocarbon, LPG, chlorine etc. utmost care is required to ensure safe joint. Normally metal compression fitting (rings and nuts) are used. Softer ring is preferred over hard compression ring. Nut should not be loosened. It should be frequently checked for leakage. When any leakage is noticed, first the supply cylinder valve should be closed instead of operating any electric switch or spark generating device.
Semi-conductive material for hoses preferred over non-conductive. Connection or opening the line for repair or maintenance. For outside servicemen it is most useful.
Colour bands are superimposed on the ground colour. Minimum width of colour band is 25 mm. Width ratio of first band to second band should be 4:1.
Size of lettering should be as under:
|Outer Dia of Pipe
|20 to 30||10|
|30 to 50||20|
|50 to 80||30|
|80 to 150||40|
Where flow direction is to be indicated, arrows or letters are painted near valves, junctions etc. and at suitable intervals along the pipe.
Precautions in Breaking Pipelines:
Following precautions are necessary while opening or breaking any pipeline:
- Prepare work permit Tag the joint or portion to be broken.
- Close or lock the isolation valves to stop flow in the line to be opened. Isolate the area.
- Stop pump and motor. Remove fuse so that motor cannot be started.
- Drain, vent and cool the line completely. See that the pressure is zero and the pipe is cool.
- Wear PPE like hand gloves, face shield, apron, respirator etc. depending on chemical. Keep fire extinguisher ready.
- Support the line on both the sides of joint. If it can fall, hold it by a lifting machine. Flange nuts and bolts should be opened slowly. A temporary flange guard should be put so as to protect from splashes or dripping. First the farthest nut-bolt should be loosened so that splash if any may not come toward the body. Dripping, if any, should be allowed fully. Then the adjacent nut bolts should be opened. To separate flanges, a metal wedge may be used if necessary. Final bolt will be opened only after completion of dripping. Spark should be avoided.
- After removing choking by scrapping, digging or drilling the removed section of the line, valve etc should be decontaminated by water, air or purging inert gas. If this is not possible, it should be tagged with warning indicating the contaminant.
- Use stable platform working by sitting on other pipelines, ladder or structure is risky.
- Safety shower, running water hose, fire, extinguisher, absorbent etc. should be kept ready for use.
- More precautions should be taken while opening dead lines or pipes whose content is not known.
- Direct cutting by hacksaw or gas flame without knowing the content is hazardous. Flammable, corrosive or toxic content must always be removed first.
From storage at production place, chemicals are transferred or transported to an user place or another storage place. It may be from one place to another outside place or within the factory premises.
Chemicals are transferred in solid, liquid or gaseous forms. Solids are transferred in lumps or power from and may generate dust, for which dust compression or extraction system is necessary. Liquids are transferred by gravity, pumping or by water, air or inert gas pressure. Splashes from vessels, pipes, joints, pumps, glands, valves and cracks are possible. Control of flow rate, safety showers, absorbents and personal protective equipment become necessary. Gases can leak through cylinders, valves, pipes, joints, vessels, gauges etc. Flow rate control, scrubber, condenser, venting and safe discharge are essential.
(1) Through pipelines: Most plants have a system of storage tanks for liquids or even materials which can be easily melted. The liquids are pumped to measuring tanks from where they are charged to the reactors.
Safe practice is to pump to the measuring tank and an overflow line returning to the tank.
The pipelines can be of various materials depending upon the nature of chemicals handled steel, stainless steel, polythene, polypropylene, PVC, glass, lead, glass lined, rubber lined. The pipelines should be well laid, giving adequate support, provision for maintenance, and painted for correct identification, as per IS:2379. Pipelines carrying LPG and flammable material should be properly bonded and earthed Isolation valves should be provided for easy control in case of breakage and maintenance.
(2) Drums: While handling liquids from drums, the material can be emptied by sucking into a measuring vessel or by pumping out, using a small pump that could go into the bung opening or by a gear pump. Air pressure should not be used, more so with toxic or corrosive liquids. Transfer by vacuum and using necessary PPE is the best procedure.
Solids can be discharged into reactors by drums tilters or emptied onto specially designed screw conveyor. Cut drums should not be invariably as workers are not careful to hammer down the sharp edges. Partially used drums must be covered, special protection should be taken to preserve the chemical and the product identified. Empty drums are not really empty, if they have been used for solvents unless specially cleaned.
Dangerous chemicals like dimethyl sulphate, benzoyl chloride, etc. require elaborate cleaning to really wash out the traces of harmful ingredients.
(3) Naked carboy and glass bottles should never be transported. They should be transported in wooden crates or cases, properly closed and handled to avoid damage to the container.
(4) Plastic Carboys are very easy to handle and sturdy. Special spouts are usually provided to prevent spillage.
(5) Conveyor belts are frequently employed for handling large quantities of chemicals. When dealing with organic powers, steps should be taken to see that static charge is not generated.
(6) Pneumatic conveyors are increasingly used for transportation from one place to another within plant.
(7) Gas cylinders should be handled with the right type of tackle, trolley and certainly not thrown down. They should be protected against the heat and impact. When kept vertical, they should be clamped or tied to prevent fall.