Selection and Limitations of Piping Components
Contents:





Pipes and Fittings
Comments on selection and Limitations of Components
Piping Joints
Fabrication, Assembly and Erection of Process Plant Piping
Examination , Inspection and Testing
Pipe and Fittings
Furnace lap weld ferrous pipe, furnace butt-weld ferrous pipe, spiral-weld ferrous pipe, and
fusion-welded steel pipe (made to ASTM A134, A53, Type F, API 5L furnace butt welded and
A211) are not permitted for hydrocarbons or other flammable fluids within process unit limits
or for hazardous fluids in any location. Non-ferrous pipe made by similar manufacturing
process is similarly restricted.
The use of bell-and-spigot fittings is limited to water and drainage service. Also, pipe
couplings made of cast, malleable, or wrought iron are not permitted for flammable fluids
within process limits or hazardous fluids in any area. In addition, they cannot be used for
flammable fluids outside process unit limits at design temperatures above 300°F or design
pressures above 400 psig.
Comments on Selection and Limitations of Components
There are many Code mandated restrictions for the use of fittings, bends, intersections, and
valves which are not universally applicable to all process plant services, and such components
are not easily codified. Some guides, however, are of value to the designer and are listed:

Welding fittings are usually preferred to flanged fittings, not only for economic reasons
but because the potential for leakage is reduced.

Pipe bends are preferred to butt welding elbows for reciprocating compressor suction
and discharge piping, vapour relief-valve discharge piping, and piping conveying
corrosive fluids (such as acid where turbulence in a fitting may cause excessive
corrosion).

Bends or dead end tees should be used for piping which conveys pulverized abrasive
solids suspended in gas in the dilute phase. Dead end tees (so arranged that the flow
will impinge against the dead end) have a longer life than bends in abrasive service
and should be used if the system can be designed to accommodate the resulting
increase in pressure drop.

Bends should be used for dense phase flow of pulverized abrasive solids and for all
piping which handles either pulverized or granular solids suspended in liquids or
granular solids suspended in gases.

If the flow is through a branch into a header (or run pipe) in a piping system which
transports pulverized abrasive solids suspended in gas in the dilute phase, a dead end
cross (so arranged that the flow will impinge against the dead end) should be used.

In services with very high corrosion rates, butt welding fittings with the same inside
diameter (ID) as the attached pipe (if not the same, consider taper boring the
component with the smaller ID) are preferred to threaded and socket welding fittings.

Threaded cast iron fittings should not be used in pressurized process and utility
piping.

Threaded plugs are preferred to pipe caps for threaded end closures to reduce dead
end corrosion problems.

In most process plants, internal corrosion is a greater problem than external
corrosion. Consequently, it is common practice that all 3/4 in and larger steel and cast
iron (and all 2 1/2 in and larger brass) gate, globe, and angle valves (located above
grade) be of the outside screw and yoke type.