WHAT'S IN ASME B31.1 POWER PIPING?

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
Requirements

Ø  Pressure
Design Requirements

Ø  Valve
Requirements

Ø  Fabrication and Installation

Ø  Inspection, Examination and Testing

B31.1
Scope

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. (100.1)

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

•    
steam

•    
water

•    
oil

•    
gas

•    
air     [100.1.2]

Boiler
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

•     
Inspection

Organization
of the Code

I Scope and Definitions

II Design

III Materials

IV Dimensional
Requirements

V Fabrication, Assembly,
and Erection

VI Inspection,
Examination and Testing

Appendices
similar to ASME B31.3 except

II Rules for Design of
Safety Valve

Installations

IV Corrosion Control

V Recommended Practice
for Operation,

Maintenance and
Modification

VII Design of Restrained
Underground Piping

B31.1
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
Piping

Ø Steam
Trap Piping

Ø Pump
Suction and Discharge Piping

Ø District
Heating and Steam Distribution Systems

Fluid
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
Requirements

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)

Ø OD
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

Flanged
Joint Requirements

B31.1 has detailed
requirements for flanged

joints. Requirements
include:

·      
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

Most
Materials – (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

B31.1

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 &
Temperature

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 -
conditions:

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

Valve
Requirements

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

Nonstandard
Valves Shall be of a design…which the manufacturer recommends for the
service

All
Valves

Ø must
have “blow-out proof” stems

Ø OS&Y
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)

Fabrication
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

ØASME B31.3
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
range

Fabrication
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.

Inspection,
Examination and Testing

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

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
accessible

·      
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%
SY

·      
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

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Whats in ASME B31.3