Piping Engineering / Design Blog.



Posted by Antony Thomas at Wednesday, October 26, 2011

What’s in ASME B31.1 (Power Piping)?

Ø  Scope

Ø  Organization
of the Code

Ø  Fluid
Service Requirements

Ø  Bases
for Allowable Stresses

Ø  Material

Ø  Pressure
Design Requirements

Ø  Valve

Ø  Fabrication and Installation

Ø  Inspection, Examination and Testing


Rules for this Code
Section have been developed considering the needs for applications which
include piping typically found in electric power generating stations,
industrial and institutional plants, geothermal heating

Systems and central and district
heating and cooling systems.

Power piping systems as
covered by this Code apply to all piping and their component parts…They include
but are not limited to





air     [100.1.2]

External Piping (BEP)

Generally defined as
piping between the boiler and the first block valve.

Ø Technical
requirements are in accordance with B31.1

Ø Administrative
requirements are defined in ASME B&PV Code Section I and include
requirements for

B&PV Code stamp

Data reports

Quality control


of the Code

I Scope and Definitions

II Design

III Materials

IV Dimensional

V Fabrication, Assembly,
and Erection

VI Inspection,
Examination and Testing

similar to ASME B31.3 except

II Rules for Design of
Safety Valve


IV Corrosion Control

V Recommended Practice
for Operation,

Maintenance and

VII Design of Restrained
Underground Piping

provides specific requirements for

Ø Boiler
External Piping (Steam, Feedwater,

Ø Blowoff,
Blowdown and Drains)

Ø Blowoff
and Blowdown Piping (Non-BEP)

Ø Instrument,
Control and Sample Piping

Ø Spray
Type Desuperheater Piping

Ø Pressure
Reducing Valves

Ø Pressure
Relief Piping

Ø Piping
for Flammable or Combustible Liquids

Ø Piping
for Flammable Gases and Toxic Fluids

Ø Piping
for Corrosive Fluids

Ø Temporary

Ø Steam
Trap Piping

Ø Pump
Suction and Discharge Piping

Ø District
Heating and Steam Distribution Systems

Service Requirements

Ø B31.1
does not define specific fluid services, but does have limitations for piping
systems handling certain fluids

Ø Specific
requirements for components and joints are described in paras. 105-118.

Ø Furnace
butt welded pipe is not permitted for flammable, combustible or toxic fluids

Joint Fluid Service

Ø Socket
welding size limited for BEP and toxic fluids

Ø Threaded
joints size limited by temperature and pressure; example maximum pressure for
NPS 3 joint is 400 psi (2750 kPa)

Ø Pipe
thinner than STD WT may not be threaded

Ø Pipe
shall be Sch 80 seamless for

Steam over 250 psi (1750 kPa)

Water over 100 psi (700 kPa) and 220ºF (105ºC)

tubing compression and flared tubing limited to 2 in. (50 mm)

Ø Brazed
joint may not be used for flammable or toxic fluids in fire hazard areas

Ø Soldered
joints may not be used for flammable or toxic fluids

Ø Soldered
joints may not be used in piping subject to vibration

Joint Requirements

B31.1 has detailed
requirements for flanged

joints. Requirements

Class 150 steel flanges bolted to Class 125

cast iron flanges are required to be flat faced…gasket required
to be full face.

Bolting dimensions for both US customary and metric bolting

·       Bolt
material requirements as a function of flanges and gaskets

Bases for
Design Stresses

– (materials other than gray iron, malleable iron and bolting)
below the creep range, the lowest of

the specified minimum tensile strength divided by 3.5

1/3 of tensile strength at temperature

2/3 of specified minimum yield strength

2/3 of yield strength at temperature; except for austenitic
stainless steels and nickel alloys with similar behavior, 90% of yield strength
at temperature

Material Requirements

Ø Materials
for BEP must meet ASME B&PV Code requirements; unlisted materials may not
be used

Ø Unlisted
materials may be used for OD tubing compression and flared tube fittings.

Ø Use at
temperatures above maximum in stress tables generally not permitted.

Ø No
rules for use at temperatures below -20ºF (-29ºC)

Pressure Design

The rules for pressure
design are essentially the same as for ASME B31.3, but they are not identical.

The two Section
Committees are working to make the requirements the same.

Design Pressure &

Allowance for pressure and temperature

variation: The
Code allows the design pressure to be set below the most severe coincident
pressure and temperature for the

following variations:

Ø Can
exceed allowable by 20% for no more than 1 hr/event and no more than 80 hr/year

Ø Can
exceed allowable by 15% for no more than 8 hr/event and nor more than 800 hr/year

allowance for pressure and temperature

variation -

Ø Except
as limited by component standards

Ø Except
as limited by manufacturers

Ø No
limitations on cast iron or other non-ductile

Ø components

Ø No
limitations on yield strength

Ø No
limitations on longitudinal

Ø No
limitations with respect to test pressure

Ø No
permission from the owner required


Can be used within their pressure-temperature ratings and any
additional limitations described in the Code

Shall be of a design…which the manufacturer recommends for the


Ø must
have “blow-out proof” stems

required for NPS 3 and larger above

Ø 600 psi
(4150 kPa)

Ø screwed
bonnets not permitted for steam

Ø above
250 psi (1750 kPa)

and Installation

Ø Welder
& brazer qualification and bending & forming requirements are very
similar but not identical

Ø Preheating
and heat treatment

Ø requirements
are different

requires neither preheating or heat

Ø treatment
for carbon steel with thickness less

Ø than or
equal to 3/4 in. (19.0 mm)

Ø B31.1
requires preheating to 200ºF (95ºC) or heat treatment for the same thickness

and Installation

Ø Minimum
socket weld size is 1.09 times nominal wall thickness versus B31.3 requirement
for 1.25 time pressure design Thickness

Ø Flange
faces are required to be fitted so that gasket contact surfaces bear uniformly
on the gasket

Ø Bolts
must be threaded through the nut.

Examination and Testing

Ø Similar
distinction between inspection and examination, but no specific “owner’s

Ø Authorized
inspector required for boiler external piping, ASME B&PV Code, Section I

Ø B31.1
does not include the concept of random with progressive examination… either
100% or none

Visual examination is required
for all welds with para. 136.4.2 acceptance criteria

No surface cracks

No surface undercut <1/32 in. (1.0 mm)

Limits on weld reinforcement

No surface lack of fusion

No incomplete penetration…applies when inside surface is readily

BEP requires hydrotest in accordance with

ASME B&PV Code, Section I

Non BEP requires hydrotest or, at the owner’s option, pneumatic,
sensitive leak or initial service leak testing.

Lines open to the atmosphere do not require testing

Joints must be exposed for examination during leak testing,
except that insulated systems may be tested by fluid loss over time method.

Pressure must be held a minimum of 10 minutes, and then may be
reduced to design pressure for leak examination period.

Stress during hydrotest is limited to 90% SY, rather than 100%

Hydrotest pressure is 1.5 times the design pressure…no
temperature correction

Pneumatic testing requires owner’s approval

Pneumatic test pressure is 1.2 to 1.5 times the design pressure

Download the Entire file by clicking the below link
Whats in ASME B31.3


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