PIPING-KNOWLEDGE

EQUIPMENT LAYOUT

Basic engineering supplier provide the initial information for doing equipment layout work. Piping Department does layout studies in consultation with process, civil, electrical, instrumentation, operations, maintenance and construction for preparing the equipment layout.
With the help of PFD, P&ID, Site Plan, Vendor data, Equipment Data sheets, Plant North, prevailing wind direction and below mentioned points, equipment general arrangement should be prepared to finalize overall plot size required, major structural requirement, pipe rack widths, access roads and widths etc. Plot Level and grading plan to be taken from Civil and incorporated in the Equipment Layout.
To start equipment layout ,one should have basic idea of flow sequence of raw material and finished product. The sequence of flow should start from one end near battery limit. This battery limit basis should be finalized on basis of overall site plan and interconnecting piping.
The major equipment's as per PFD and basic equipment list should then divided into sub system or blocks which consist of interconnected equipment's. Interconnection between various system to be studied. Once the interconnectivity is established , next step is to arrange equipment as per inter-distance and access requirement obtained from OISD-118 or Project specification.
Study should be required to find out which equipment should be elevated for gravity flow requirement, or which can be elevated for saving floor space, economy and other related advantages and disadvantages. Planning should be done for staircase location, fire and emergency exit and drop zone from the structure.

Various Factors to be considered to develop equipment layout :

PROCESS REQUIREMENT
LAYOUT SPACE AVAILABILITY
EQUIPMENT SIZE
UNDERGROUND FACILITIES REQUIREMENT
PIPE RACK
ROAD, ACCESSWAY, PAVING
PLANT LAYOUT SPECIFICATION
ECONOMIC PIPING
COMMON OPERATION
FUTURE EXPANSION

EQUIPMENT LOCATION PHILOSOPHY :

Process unit shall be located on high ground to avoid flooding.
process units should be located in block type layout for fire fighting purpose.
PIB, control rooms and substation shall be located at edge of unit adjacent to road at a safe distance from equipment.
Road access to be provided from all four directions to a process unit for effective fire fighting and dead ends to be avoided.
Equipment should be arranged alongside the rack as rack is consider main artery of a unit.
Wind direction: Equipment layout should be done considering prevailing wind direction to avoid travel of hydrocarbon/toxic gases.
Equipment in Process unit shall be arranged in a sequential order of process flow to minimize pipe run length.
Layout should allow easy access to all equipment and adequate space and access for piping and instrumentation.
Emergency escape route ,provide alternate escape routes from potentially dangerous areas subject to fire and hazards.
Equipment layout and plot plan is used to schedule erection sequence of plant equipment at grade or in structures which include rigging studies for large lifts, Cranes & Derricks.
Inter distance between equipment and various facilities to be in accordance with OISD-STD-118 & project specification & requirement.

Plant layout needs statutory approvals before implementation. Some of the statutory approving codes are:

1. Indian Factories Act

2. Indian Explosives Act

3. Petroleum Act

4. Central / State Pollution Control Board Law

5. Indian Electricity Rules

6. CIVIL aviation rule - National Airports Authority

7. Insurance Association of India - Fire Protection manual.

8. N. F. P. A. Code of Practice.

Following Design Data Required:

Licensor/basic engineering supplier data : Capacity of process unit, indicative equipment approximate dimension, Block flow diagram, Utility requirement.
Process Data : PFD, P&ID , Process data sheet, Hazardous nature of unit, Operating philosophy.
Civil Data : Plot Level, Grading plan.
Metrological Data: Wind direction, Rainfall
Electrical data: Electrical hazardous area classification, substation size.
Instrumentation data : Analyzer house requirement, PIB sizes.
PDP data : Site plan & ISBL/OSBL battery limit interface location.
Statutory requirement : OISD,PESO,IBR,OSHA etc.

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BUTTERFLY VALVE

Butterfly valves are quarter-turn valves that are popular for on-off or modulating services. They are lightweight, have a small installation footprint, lower cost, quick operation, and are available with large orifice sizes. The “butterfly” is a disk connected to a rod. When the valve opens, the disk rotates to allow fluid to pass through. It closes when the rod rotates the disc by a quarter turn to a position perpendicular to the flow direction.

3 Main Butterfly Valves Types:

1) Zero-Offset Butterfly Valves:

Concentric or Rubber Seated are other names for the Zero-offset Design. Zero-offset means there is no offset by the stem of the valve. the valve seals via interference along the disc edge at the stem between disc and the rubber seat.

The rubber seated valves has the lower (up to 250 psi) and withstands heat up to 400°F. Its rubber seat encases the body to prevent contact with material which maintains the purity of media.

2) High-Performance Double Offset Butterfly Valves:

This type of valve is refereed to as double offset because the offset is in two places, at the line of the disc seat/body seal, and the bore. Off-center positioning increases durability for the seal. High-performance valves tolerate pressure up to 1440 PSI and temp up to 1200°F.

3) Triple Offset Butterfly Valve:

The best type of butterfly valve for high-pressure systems is the triple offset butterfly valve. This valve is most advanced with Lower emissions and is designed to work with various environments. Its heat tolerance is 1200°F as it can withstand 1480 psi.

working principle

The construction of a butterfly valve is relatively simple, with the rotation of the valve disc controlling the fluid flow. In the closed position, the disc blocks the valve bore while in the open position, the disc is oriented perpendicular to the flow direction to allow flow. Butterfly valves generally provide bi-directional flow and shutoff capability. However, they are not full-bore, which renders them unsuitable for pigging or swabbing. The body material is ductile iron with an epoxy powder coat on both internal and external surfaces. The valves are typically operated by handwheels, gears, or actuators, or a combination thereof, according to the specific application requirement and technical specifications.

Butterfly valve parts

Below are the major butterfly valve components:

Valve Body
The valve body fits between the pipe flanges - the most common end connection types being flanged, double lug, and wafer types.
Disc
Attached to the valve body is the disc that functions as a gate that stops or throttles fluid flow; it can be considered equivalent to a gate in a gate valve, or a ball in a ball valve. The disc is typically bored to receive the stem, or shaft. There are many variations in disc design, orientation, and material in order to improve flow, sealing, and/or operating torque.
Seat
Lining the internal valve body is a strong elastomer or metal anti-leak seal that secures the disc in place in the closed position in order to achieve complete shutoff. stainless steel weld filled and microfinished integral body seat ensures a corrosion and erosion resistant seat face.
Stem
The valve shaft, often also referred to as the stem, is the component that connects the disc to the actuation mechanism and transmits the torque through itself.
Seals
Seals are present at multiple interfaces within the valve to either ensure a tight seal during operation or to isolate the process media from the valve’s internal components for a more flexible and cost-efficient design.

Sealing on seat face is ensured by a continuous T-profile resilient sealing ring which is held on the periphery of the disc by a retaining ring, preventing the sealing ring from rolling out. In the closed position, the sealing ring is pressed against the seat face, providing a tight seal on both the upstream and downstream ends. In the open position, the sealing ring is completely unstressed due to the double eccentric disc design.

Advantages of butterfly valves

Depending on the application, butterfly valves can offer significant advantages over other types of valves, especially for dimensions over DN 200 (200 mm) in size:

Lightweight and Compact: With a compact design and a smaller face to face dimension, butterfly valves have a considerably less installation footprint and offer savings in the form of lower installation costs including labour cost, equipment, and piping support.
Low Maintenance Requirements: An inherently simple, economic design that consists of few moving parts, and hence fewer wear points, significantly reduces their maintenance requirements.
Fast Acting: A 90° rotation of the handle, or the actuation mechanism, provides a complete closure or opening of the valve. However, with larger butterfly valves, a gearbox is often required as part of the actuation mechanism which reduces the operational torque and simplifies the operation of the valve but comes at the expense of speed.
Low Cost: Owing to their simple design, butterfly valves require less material and are simpler to design and manufacture and are often the more economical choice compared to other valve types.

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Flare System & its Requirements

Gas flaring is a combustion device to burn associated, unwanted or excess gases and liquids released during normal or unplanned over-pressuring operation in many industrial processes, such as oil-gas extraction, refineries, chemical plants, coal industry and landfills.

Flare systems provide for the safe disposal of gaseous wastes. Depending on local environmental constraints, these systems can be used for:

1) Extensive venting during start up or shutdown
2) Venting of excess process plant gas
3) Handling emergency releases from safety valves, blow-down, and depressuring systems

- Design will vary considerably, depending on the type of connected equipment and complexity of overall system. A flare system generally consists of an elevated stack, means to maintain burning conditions at the top of stack.

- Whenever industrial plant equipment items are over pressurized, the pressure relief valves provided as essential safety devices on the equipment automatically release gases and sometimes liquids. Those pressure relief valves are required by industrial design codes and standards, as well as by law.

- The released gases and liquids are routed through large piping systems called flare headers, to a vertical elevated flare. The released gases are burned as they exit the flare stacks. The size and brightness of the resulting flame depend on the flammable material’s flow rate in terms of joules per hour.

Working of flare system:

Based on height of flare tip, flares can be categorized into two types:

Ground flare:

1) Open ground flare
2) Enclosed ground flare

Elevated flare:

1) Self supported flare
2) Derrick supported flare
3) Guyed stack flare

Types of flare based on mixing at flare tip:

1) Steam assisted flares
2) Air assisted flares
3) Pressure assisted flare
4) Non-assisted flare

Ground Flare:

A Ground Flare is where the combustion takes place at ground level. It varies in complexity and may consist either of conventional flare burners discharging horizontally with no enclosure or of multiple burners in refractory-lined steel enclosures. Ground flares is the preferred choice only if plant is located in an area where it is highly desirable to have a flare which is not visible in public.

Open Ground Flares:

Here Flare Headers distribute and the flaring occurs at ground, with the area surrounded by radiation fences. Most have multiple burners that combine to flare large amounts of gas. The burners are located either in a refractory lined enclosure or in a pit. Open ground flare can combust large quality than enclosed flares. Another type of ground flares is the horizontal flare which is located in an open pit.

Enclosed ground flares:

Enclosed ground flares are the most practical ground flare type for industries located in city areas. While they are expensive, they provide a means of smokeless combustion without a flame visible to the surrounding area. Hot combustion gases from an enclosed ground flare are discharge to the atmosphere through an opening at the top of the refractory lined enclosure.

Elevated Flares:

For safety reasons it’s a advantage to have flares at considerable height from ground. Elevated flares are preferred over enclosed ground flares due to lower costs. Elevated flares are also preferred over open pit ground flares due to lower land requirements.

Self-supported flares:

The self-supporting stack is a freestanding stack anchored to a base Self-supported flare system is used for lower heights when radiation exerted is low. It uses less space for installation. Self-supporting flares are generally used for lower flares tower heights 9mtr to 30mtr but can be designed for up to 75mtr.

Derrick supported flares:

The derrick supported stack is located in the centre of a derrick structure and is held to the structure by tie rods and guides. Derrick supported flares can be built to a considerable height since the system load is spread over the derrick structure. Derrick supported flare system is optimum installation for higher heights where high radiation is exerted. Derrick supported flares are the most expensive design for a given flare height. The derrick supported stacks have been built for around 120mtr Height.

Flare gas transportation Piping:

Waste gases from vents, blowdown gases released from pressure relief devices are sent to the flare stack through the gas collection header. This piping should be designed to have minimum pressure drop. Potential dead legs and liquid traps are avoided. Use of valves in this line should be kept to minimum and when used should be sealed to open position. The piping should be equipped for purging so that explosive mixtures do not occur in the flare system either on start up or during operation. Minimum slope of the flare header shall be 1:450 (as per API 521).

Vessels & Drums used in Flare system:

Mainly four type of vessels or drums used in design of flare system:

1) Knockout drum

2) Blowdown drum

3) Quench drum

4) Seal drum

Knockout Drum:

Liquid present in the vent stream or liquid that may be condense out in collection header and transfer lines are removed by the Knockout drum. The knockout drum may be horizontal or vertical type.

A knockout drum is required where enough hydrocarbon liquids are entrained with or condensed from gas to avoid possible fire hazards from liquid droplets falling out of the flare. The function may be combined with that of blowdown drum to provide a single drum, where small quantities of liquid are involved.

The knockout drum may be either horizontal or vertical. Horizontal drums are more common for large relief loads for the following reasons:

-The required elevation of the relief header is lower than for a vertical drum.

-The horizontal drum would cost less than the vertical drum which has equivalent capacity.

Blowdown drum:

Blowdown drum is used when sizable liquid releases from process is required to be captured. The releases may be intentional like drainage from liquid drain system during shutdown or start up- or emergency vents of PSV discharge. The drum may be capable of accepting the anticipated liquid loads without filling beyond maximum operating level of drum. This maximum operating level must provide a gas flow path with sufficiently low gas velocity to allow gravity separation and prevent re-entrainment beyond design droplet size. Blowdown drums is located near sources, close to battery limits of a process unit or area to reduce to reduce amount of piping subject to two phase slug flow.

Quench drum:

A quench drum can be used to condense vapour discharge from relief device for either later return into the process after relieving condition has passed or for disposal to sewer. Generally a Quench drum is provided whenever the material being relieved is too valuable to be burned in a flare or too toxic to be relieved to atmosphere. A Quench drum can be used to cool hot material so that the entire relief system does not need to be designed for higher temperature. Other purpose for quench drum is to quench runaway reactions.