Chemicals are transferred by pipeline and also by different types of containers. The safety aspects are stated below.
Safe transfer of Chemical by Pipeline
Pipelines are required to carry a variety of materials such as water, steam, air, oil, gas (inert or toxic, vapor 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. Pipework 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:
The 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 the working platform, and testing, and maintenance.
The material of construction is selected depending on nature (corrosively, toxicity, flammability, etc.), quantity weight, flow, pressure) and other parameters like temperature, viscosity, color, expansion, etc. The thickness of the 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 intergranular 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 a variety of pipes, their fittings, threads, color code, etc, see BIS handbook), ASME (American Code), British Standard (e.g BS 1710, 1319, 537, 4159) and International Standard ISO R 508 for colors for pipes for inland installations and onboard ship, Indian Boiler Regulations also provide details for pipe selection, design, fabrication, and testing for boiler purposes.
Safety Aspects of Pipework:
Generally, the probability of leakage pipelines is proportional to the length of pipelines, the number of joints, valves, vents, bleeds, drains, etc. and complexity such as the number of pump connections, recycle streams, hours of work, etc. Therefore it is advisable to-
- Minimize 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 the 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 storage tanks, painting with color-coding (IS:2379) and cathodic protection where required.
More pipework in dyke is not desirable particularly with hazardous chemicals, as it may be trapped in a fire in the dyke. Similarly, pipelines of the flammable or toxic chemicals should not be laid in the tunnel, as its leak may spread from one area to another area. Electric cables or hotlines and flammable gas or liquid lines should not run side by side. The solvent line should not be laid below the corrosive line. Seam joints of rubber lined pipes should be kept upward.
The 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 insides. 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.
The auto control valve should have a 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 devices, liquid seal, manual vent, etc. should be provided to depressurize the system where necessary.
Many different types of valves exist. It is essential to choose the type best suited for the particular 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 a 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 ensure 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.
The 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.
A softer ring is preferred over a hard compression ring. The 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.
Color bands are superimposed on the ground color. The minimum width of the color band is 25 mm. The width ratio of the first band to the second band should be 4:1.
The 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:
The following precautions are necessary while opening or breaking any pipeline:
- Prepare work permits 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 the pump and motor. Remove the fuse so that the 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 the chemical. Keep fire extinguisher ready.
- Support the line on both sides of the 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. The final bolt will be opened only after the completion of dripping. Spark should be avoided.
- After removing choking by scraping, 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 a warning indicating the contaminant.
- Use a 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 deadlines 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 the production place, chemicals are transferred or transported to a 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 that 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 conveyors. Cut drums should not be invariable 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 sulfate, benzyl 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 the static charge is not generated.
(6) Pneumatic conveyors are increasingly used for transportation from one place to another within the plant.
(7) Gas cylinders should be handled with the right type of tackle, trolley, and certainly not thrown down. They should be protected against heat and impact. When kept vertical, they should be clamped or tied to prevent falls.