Learn Basic of Piping Engineering: Chapter-2

CHAPTER 2

PIPE

INTRODUCTION:

Ø A pressure tight cylinder used to convey fluids under pressure through materials of

commercially available designation.

Ø Pipe is always designated through nominal bore size(NBS) also called as nominal pipe

size(NPS)

Ø A pipeline conveys a fluid from one given point of the plant usually called inlet

point of the line, to another part of the plant usually called outlet point of the line.

NOMINAL PIPE SIZE (NPS):

Pipe size is specified with two non-dimensional numbers: a Nominal Pipe Size (NPS) and a schedule (SCH). The relationship of these numbers to the actual pipe dimensions is a bit strange.

The NPS is very loosely related to the inside diameter in inches, but only for NPS 1/8 to NPS 12.

For NPS 14 and larger, the NPS is equal to the outside diameter (OD) in inches. For a given NPS, the OD stays constant and the wall thickness increases with larger SCH. For a given SCH, the OD increases with increasing NPS while the wall thickness increases or stays constant.

NOMINAL DIAMETER (DN):

It is same as nominal pipe size, but in mm.

SCHEDULE (WALL THICKNESS):

Schedule:

Carbon steel : 5, 10, 20, 30, 40, 60, 80, 100, 120, 160.

Stainless steel : 5S, 10S, 20S, 30S, 40S, 60S, 80S.

Weight series:

STD : Standard
XS : Extra Strong
XXS : Double Extra Strong

Wall thickness is designated by schedule number or descriptive classification, rather than the actual wall thickness. The original thicknesses were referred to as standard (STD), extra strong (XS) and double extra strong (XXS).

Wall thickness for the schedule 40 and STD are same for sizes ⅛ to 10”.schedule 80 and XS also have the same wall thickness for ⅛ to 8” diameter pipe.

CODES:

Ø ASME B36.10 - CARBON STEEL

Ø ASME B36.19 - STAINLESS STEEL

MATERIAL:

Carbon steel:

Steel is basically a solution of carbon (C) into iron (Fe). The presences of

carbon into the crystal structure of the iron improve very much the mechanical characteristics of the iron alone. Carbon steel is a conventional denomination for steel that has almost no other metallic elements added into it.

Carbon steel material specification ASTM A106 is available in grades A, B

and C. These refer to the tensile strength of the steel, with grade C having the highest strength.

Common practice is to manufacture the pipe as A106 grade B

ASTM A53 is also commonly specified for galvanized or lined pipe or as an

alternate to A106.the testing requirement for A53 are less stringent(rigorous or tight) than for A106. Three types of carbon steel pipe are covered by A53. These are type E or Electric resistance welded, type F or Furnace-butt welded, and type S or Seamless. Type E and S are available in grade A and B, comparable to grades A and B of A106.

Stainless steel:

Austenitic stainless steel pipe commonly referred to as “Stainless Steel” is

virtually non-magnetic. Stainless steel is manufactured in accordance with

ASTM A312 when 8” or smaller sizes are needed. There are eighteen different grades, of which type 304L is the most widely used.

Grade 316L has high resistance to chemical and salt water corrosion and is

best suited for welding. Large sizes (8” and up) of stainless steel pipe are covered by ASTM A358. Extra light wall thickness (schedule 5S) and light wall thickness (schedule 10S) stainless steel pipe is covered byASTM A409.

PIPE MANUFACTURING METHOD:

Ø Seamless

Hot rolled, cold drawn etc

Ø Electric resistance welding

No material is added during welding process

Ø Electric fusion welding

Filler material is added during welding process

CHARACTERISTICS OF A PIPELINE:

Ø Nominal pipe size(NPS)

Ø Wall thickness

Ø Type of joint between pieces

Welded joints

Ø Butt welded

Ø Socket welded

 Threaded joints

 Flanged joints

Ø External finishing

 Painting

 Insulation

OTHER CHARACTERISTICS OF A PIPELINE:

Routing:

Ø The routing is how the Pipeline is developed into the space.

Ø There are rules and regulations to route a Pipeline according the

“Good Engineering Practice”

Ø Cold Pipelines connecting static objects (something that does not move

like Tanks, Vessels, other Pipelines, and Headers) can be straightly

routed between the inlet and the outlet point.

Ø Cold Pipelines connecting machines that vibrate or rotate may need a

flexible part between the inlet and the outlet point.

Ø Hot Pipelines must be flexible enough to adsorb the thermal expansion

of the Pipeline from cold to hot condition

Supporting System:

Ø Every Pipeline must be supported. Not all Pipelines are supported in

the same way.

Ø Cold Pipelines can be supported everywhere with fixed points

Ø Hot Pipelines cannot be supported only with fixed points, but certain

points must be only guided, meaning that in those points the Pipeline

retains a certain numbers of degree of freedom in certain directions,

while are constrained in certain other directions.

TYPE OF JOINT BETWEEN PIECES:

1. Butt welded joint:

The end is machined to allow head to head full penetrating welding

2. Socket welded joint:

A socket is provided where pipe can be inserted

3. Threaded joint:

Parts to be connected are threaded.

PIPE ENDS:

Pipe may be obtained with

Ø Plain ends are cut square and reamed to remove burns. This

type of end is needed when being joined by mechanical couplings, socket weld fittings, or slip-on flange.

Ø Bevelled ends are required for most butt weld application.

Ø Threaded ends are used with screwed joints and are ordered

noting threaded on both ends or one end.

Various combination of pipe end:

POE: Plain one end
PBE: Plain both end
BOE: Bevelled one end
BBE: Bevelled both end
TOE: Threaded one end
TBE: Threaded both end

PIPE REPRESENTATION:

Up to 12 inch

Above 14 inch

SPECIFICATION OF A PIPE:

Example:

Size : NPS 12”

Diameter : DN 300

Wall thickness: Sch. 40

Material : ASTM A106 Gr. B

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Thursday, February 10, 2011