Piping Engineering
Recall Piping Engineering is a specialized discipline of Mechanical
Engineering which covers the design of piping and layout of equipment and
process units in chemical, petrochemical or hydrocarbon facilities
Most of the plant facilities in the petrochemical and hydrocarbon industry will
use ASME B31
Within industry, piping is a system of pipes used to convey fluids (liquids
and gases) from one location to another. The engineering discipline of
piping design studies the efficient transport of fluid.
A PIPE is a round tubular to distribute fluids and gases, designated by a
nominal pipe size (NPS or DN) that represents a rough indication of the pipe
conveyance capacity;
A TUBE is a round, rectangular, squared or oval hollow section measured by
outside diameter (OD) and wall thickness (WT), .
Tubes can come in different shapes such as square, rectangular and cylindrical,
whereas piping is always round.
The circular shape of the pipe makes the pressure force evenly distributed.
Pipes accommodate larger applications with sizes that range from a ½ inch to
several feet
PIPING FAILURES
Failures can be catastrophic, with significant losses due to damage as well as the cost
of life and pipe replacement.
Piping failures are often the first sign of a corrosion problem
WHAT IS PIPE CORROSION?
The corrosion of steel piping and its related components is a continuous and virtually
unstoppable process.
The end product, rust, is the result of an electrochemical reaction through which the
higher energy processed metal is slowly reverted back to its naturally occurring form –
metal ore.
The global cost of corrosion has been estimated at $2.5 trillion.
Beyond the astronomical cost, corrosion can stop production, cause injuries, and put a
worker’s life in danger. On top of all that, it’s sneaky and hard to spot with the naked
eye.
What Causes Corrosion?
The simplest cause of corrosion is contact. That can be when metal comes in
contact with all kinds of things, including water, oxygen, grime, or other metal.
Any of these elements can set off the problem, but each kick-starts corrosion for
different reasons.
Corrosion is a chemical reaction that plagues metals. The problem starts when a
piece of metal loses electrons and is weakened. Those electrons are encouraged to
leave when the metal is in contact with an electrolyte, like water, and electrongreedy materials.
Suddenly, the metal is vulnerable to other destructive chemical reactions. The result
can be things such as rust, cracks, and holes.
TYPES OF CORROSION
Pitting Corrosion: This type of corrosion causes tiny pits to form along the length
of the metal pipe, thus the term pitting corrosion.
Crevice Corrosion: This is where fluid ions concentrate in crevices around welds,
flanges and other types of pipe connections.
The resulting ion buildup can degrade material more quickly, which is why when
piping system leaks happen they tend to occur at the seams first.
Crevice corrosion is why there are a number of standards for welding metals, such
as stainless steel pipe, as well as many welding techniques and weld finishing
grades.
Pipe Thread Leaks
Pipe threads are an inherent point of weakness, Leaks occurring from pipe threads
are a common sight and it is usually a first sign of a corrosion problem.
Galvanic Induced Failure
Galvanic corrosions occur when different metals are in contact with each other. It
commonly occurs when carbon steel pipes are threaded to brass valves, and more
serious galvanic corrosion happens at galvanized steel to brass valve connections.
Weathering Damage
Most weathering damage occurs over a long time period due to a lack
of maintenance and the corrosion will reduce the pipe wall thickness
subjecting the pipe to leak easily.
In such cases, it is necessary to identify the structurally weaken and
damaged locations via methods such as ultrasonic thickness gauging).
Thereafter, preventive maintenance strategy e.g. applying composite
wrapping repair to reinforce the pipe wall thickness and removing the
effects of weathering directly on the pipe surface will help extend the
pipe service lifespan.
Corrosion Under Insulation
Corrosion under insulation is a widespread and typically hidden threat.
The issue can arise due to insufficient insulation thickness,
inappropriate insulation type or it is improperly installed.
Pipe leaks can occur regularly due to the difficulty to detect leaks
before it happens. It is advisable to apply readily available pipe leak
repair kits on such impromptu incidents.
Microbiologically Influenced Corrosion
Microbiologically influenced corrosion (MIC) is, by far, the most severe
and threatening form of corrosion to HVAC piping and fire protection
systems.
It is caused by the presence of various microbiological agents under
specific environmental conditions and can in some cases result in an
advanced and widespread failure of entire piping systems within only a
few years.
MIC is commonly found in closed chill water piping, especially those
winterizing with glycol, and has been documented to destroy copper,
brass, and stainless steel pipe.
Seamed Pipe Failure
Seamed pipe has a greater vulnerability to corrosion at the seam due to
many causes. In many examples, poor manufacturing practices
produce an internal or external seam which is incomplete. On the
inside, this incomplete weld seam then becomes a focal point for rust
to establish and promote higher corrosion activity, often leading to
pinhole failure.
Cooling Tower and Exchanger Corrosion
Algae and other organic growths not only interfere with operations, bu
t also accelerate many other corrosion processes and promote
microbiologically influenced corrosion. In many cases, cooling tower
maintenance and the removal of rust deposits is performed without
ever investigating the underlying cause of the problem –
Copper Pipe Corrosion
 Copper pipes are not immune to the effects of corrosion. In fact there are many
copper pipe corrosions, leaks and failures occurring.
 Failures at copper piping systems are mostly related to specific conditions or
events, such as acidic and low pH water
 galvanic activity and improper grounding or stray voltage, or high steel
corrosion activity resulting in the migration of iron oxide into the copper lines.
Consequences of Corrosion
The effects and severity of corrosion within a piping system will vary depending
on the application, but generally speaking corrosion can lead to the following
issues:

Pressure rating decreases on account of thinning pipe walls.

Flow rate can be slowed demanding more from pumps.

Fluid purity can be contaminated as the corroded pieces float away. This is a
significant concern for applications with high purity standards (e.g.
semiconductor plants).

Installation Costs will increase, as highly skilled laborers are required to weld
the system. This level of craftsmanship comes at a significant cost.
Pipe Repairs
Pipe repairs take various forms ranging from temporary pipe clamps to
pipe leak repair kits and the replacement of the pipe section.
Very often, one or multiple individual failures are fixed without further
investigation of the hidden cause.
it is necessary to adopt preventive maintenance measure to perform
composite wrapping or repairs on the affected pipe section before a
catastrophic failure happens.
5 WAYS TO PREVENT PIPE CORROSION
1. For Pipes, Watch Your Water
Water is a major corrosion causer. Especially in copper piping, too low of a pH level
can hurt the pipe’s lining. The EPA recommends you make sure your water’s pH
hovers between 6.5 and 8.5.
You’ll also want to monitor the oxygen levels in your water. Oxygen leads to rust,
and it can cause buildups and blockages.
Another good idea is to keep water temperatures low when possible. Hotter water
tends to be more corrosive.
2. Keep Pipes Clean
Microbiologically induced corrosion (MIC) happens when metals are exposed to
corrosive bacteria. It’s smart to clean pipes to prevent MIC, especially when pipes
are in contact with sulfides regularly.
3. Add Protection to All Metals
Protective linings or special coatings can prevent corrosion in pipes as
well as other surfaces. That includes things such as beams, joints, and
bolts.
For instance, galvanization works by adding a layer of zinc to metallic
surfaces such as steel or iron.
It’s also wise to use a sealant to keep corrosive bacteria from settling into
joints or crevices in the first place.
4. Keep Structures Stable
Friction, jiggling, and bouncing wear on metal. When openings start to
form, corrosive material sets in, and it can lead to crevice corrosion.
A good way to prevent crevice corrosion is to use a restraint. Things such
as U-bolts, straps, and clamps cut down vibrations that can lead to
corrosion.
5. Protect Against Metal-to-Metal Contact
 Not all metals get along. Galvanic corrosion happens when one
metal pulls electrons from another metal. The result is a weakened
section and a compromised structure.
 The best way to protect against metal-to-metal corrosion is to
insulate the metal. For piping, consider installing insulators, such
as wear pads or pipe shoes. Insulators add a buffer between
metals, so the metal stays durable longer
Piping Components and Fittings
 Fittings are used in pipe systems to connect straight pipe or
tubing sections, to adapt to different sizes or shapes, to
branch or re-direct the piping system and if necessary to
provide a joining method if 2 dissimilar piping materials are
used in the one system
The most common type of pipe fittings are:
 Elbow
 Tee
 Cross
 Reducer
 Cap
 Union
Elbow:
It is a component used in piping fittings to change the direction of a pipe run by 90 Deg or 45
Deg.
90° Elbow
45° Elbow
Tee
A tee is used to either combine or split a fluid flow. Most common are equal tees which have the
same body and branch diameter but there is also a wide range of reducing tees where either the
branch or the body is a different diameter relative to each other.
A swept tee is where the branch enters the body at an arc and is used to minimize the
frictional losses and promote flow in the system. A wye tee is where the branch is stabbed into
the body at an angle and is usually used where the branch is a smaller diameter than the main pipe.
Difference between a swept tee and a wye tee
Reducer
Reducers are used to join 2 different pipe sizes together. They can be either
concentric or eccentric which refers to the relative position of the center lines of the outlet and
inlet. Special attention must be given when using reducers in a horizontal orientation as the slope
will prevent free draining of a system if not installed correctly.
Concentric Reducer
Eccentric (bottom flat) reducer
Cap or Plug
A type of pipe fitting which is liquid or gas tight, and is used to cover the end of a pipe. A cap has
a similar function to a plug. For screwed systems the cap would have female threads where a plug
would have male threads.
Cap
Hex Plug
Cross
A cross has one inlet and three outlets, or vice versa and like tees come in equal and reducing
forms. A cross is more expensive than two tees but has the advantage of reduced space and requires
less labour to install.
FITTINGS FOR PIPE JOINTS
BSP fittings are a family of fittings used to connect up threaded pipe and equipment.
Butt weld or socket weld fittings are a type of fittings used for forming circumferential
butt weld joints in pipework systems.
They are used for critical systems and in areas where pipe-work is permanent and are
designed to provide good flow characteristics
Screwed Unions
A union is similar to a coupling, except it is designed to allow quick and convenient
disconnection of pipes for maintenance or fixture replacement. While a coupling is usually
a permanent joint or requires the ability of being able to rotate all the pipe to one side of it
to unscrew it, a union provides a simple nut transition, allowing easy release at any time.
BSP union
Flanges
Flange designs are available as:
 Weld neck
 Slip-on
 Socket Weld
 Threaded
 Stub-end or Lap flange
 Blind Flange
Weld Neck Flange
Weld neck flanges are used in critical applications. These are circumferentially welded
onto the system at their necks which means that the integrity of the butt-welded
area can easily be examined by X-ray radiography. The bores of
both pipe and flange match thus reducing turbulence and erosion.
Weld Neck Flange
Socket Flange
A socket flange is counter-bored to accept the pipe, which is then fillet welded. The
bore of both the pipe and the flange are the same to ensure good flows.
Socket Flange Flange
Slip-On Flange
A slip-on flange is slipped over the pipe and then fillet welded. Easy to use in
fabricated applications.
Slip-on Flange
Screwed Flange
A screwed or threaded flange requires no welding and is used to connect other
threaded components in low pressure non-critical applications.
Screwed Flange
Lap Flange
Lap flanges (or backing flanges) are used with a stub end which is butt-welded to the
pipe with the lap flange acting as a loose collar behind it. Thus the stub end always
provides the sealing face. This type of joint is easily assembled and aligned, and it is
favoured in low pressure applications. To reduce costs the ‘backing’ flanges can be
made from a lower grade of material such as stainless steel in Hastelloy systems.
Lap Flange
Blind Flange
A blind flange or sometimes called a blanking flange, this is used for blanking off
pipelines, valves and pumps and as an inspection cover.
Blind Flange
Valves for Piping Systems
Fluids and gassed do not just flow freely through piping systems. They must be regulated and at
certain points stopped. There are a number of different types of valves used in piping systems, the
most common types of stop valves being:
 Ball valve
 Butterfly valve
 Globe valve
 Check valves
 Diaphragm valve
 Process control valves
 Safety Relief valves
Ball Valve
A ball valve is a valve with a spherical centre which controls the flow through it. The sphere has a
hole, or port, through the middle so that when the port is in line with both ends of the valve, flow
will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow
is blocked. The handle or lever is also inline with the port through the sphere which allows the
operator to know whether the valve is opened or closed.
Manual Ball valve
Butterfly Valve
The butterfly valve like the ball valve are are part of the family of quarter turn valves, i.e. they only
require a quarter turn to achieve their fully open position. The butterfly valve can be used for
isolating or regulating flow.
The closing mechanism takes the form of a disc whose position is again indicated by the position
of the opening lever. Butterfly valves are generally favored because they are lower in cost to other
valve designs as well as being lighter in weight, meaning less support is required. The disc is
positioned in the center of the pipe, but unlike a ball valve, the disc is always present within the
flow, therefore a pressure drop is always induced in the flow, regardless of valve position.
Actuated Butterfly valve with visual indicator
Globe Valve
A globe valve is a type of valve used for regulating flow in a pipeline, consisting of a movable disktype element (the plug) and a stationary ring seat in a generally spherical body. (See section
through a globe valve below. While they can be used as a shut-off valve they are not generally
selected for this function alone as the baffle inside the valve restricts flow even when the valve is
fully open.
In a globe valve, the plug is connected to a stem which is operated by screw action in manual
valves. Typically, automated valves use sliding stems. Automated globe valves have a smooth
stem rather than threaded and are opened and closed by an actuator assembly. When a globe
valve is manually operated, the stem is turned by a hand wheel which requires 3 to 4 complete
revolutions to open or close the valve.
Check Valve
A check valve, non-return valve or one-way valve is a mechanical valve, which normally allows
fluid (liquid or gas) to flow through it in only one direction. An important concept in check
valves is the cracking pressure (or opening pressure) which is the minimum upstream
pressure at which the valve will operate. Typically the check valve is designed for and can
therefore be specified for a specific cracking pressure.
Full bodied swing check valve