What Is a Manifold Pipe?

Quick Answer

A manifold pipe (or piping manifold) is a section of large-bore pipe with multiple branch connections that collects flow from several sources or distributes flow to multiple destinations. Manifolds serve as central collection or distribution points in piping systems. The main pipe is called the “header” and the branches are connected using tees, weldolets, or branch fittings.

Manifolds are common in oil and gas production facilities, refinery process units, power plants, and pipeline stations. They reduce the number of individual piping runs and simplify flow control by centralizing valves in a single accessible location.

Types of Piping Manifolds

Type	Function	Typical Application
Production manifold	Collects well flow from multiple wells	Oil/gas production facilities
Test manifold	Routes individual wells to test separator	Well testing and allocation
Injection manifold	Distributes injection fluid to wells	Water/gas injection systems
Steam header	Distributes steam to multiple consumers	Power plants, refineries
Instrument manifold	Multi-valve assembly for instrument isolation	Pressure transmitter hook-ups
Subsea manifold	Collects subsea well flow	Deepwater production
Pipeline header	Connects multiple pipelines at station	Pipeline terminal/station

Manifold Design Considerations

Parameter	Design Criteria
Header size	Based on total flow and velocity limit (typically 3-6 m/s for liquid, 15-25 m/s for gas)
Branch size	Based on individual flow and velocity limit
Branch spacing	Minimum 2x header OD between branch centers
Branch connection type	Tee (equal branches), weldolet/reinforced branch (reduced branches)
Valve type	Gate valves (isolation), globe valves (throttling)
Material	Per process conditions: A106 Gr. B (carbon steel), A312 (stainless), A335 (alloy)
Design code	ASME B31.3 (process), ASME B31.1 (power piping)
Pipe schedule	Per wall thickness calculation plus branch reinforcement

Branch Connection Methods

Method	Size Ratio (Branch/Header)	Standard
Butt-weld tee	1:1 to 1:2	ASME B16.9
Reducing tee	1:2 to 1:4	ASME B16.9
Weldolet	Up to 1:2	MSS-SP-97
Reinforced branch	Up to 1:4	ASME B31.3
Self-reinforced tee	1:1 (extra heavy wall)	ASME B16.9
Pad reinforcement	Any ratio	ASME B31.3

ASME B31.3 requires reinforcement calculations for all branch connections. The branch weakens the header by removing pipe wall material. Reinforcement (from excess header wall, branch wall, or welded pads) must compensate for this lost area.

Wellhead Production Manifold

A typical oil field production manifold includes:

Component	Purpose
Header pipe	Collects flow from all wells
Block valves (per well)	Isolate individual wells
Check valves	Prevent backflow between wells
Pressure gauges/transmitters	Monitor individual well pressures
Test connection	Route well flow to test separator
Blowdown valve	Emergency depressurization
Pig launcher/receiver	Pipeline pigging access

Pro Tip

Spacing branch connections too close on a manifold header creates stress concentration zones where the reinforcement areas of adjacent branches overlap. ASME B31.3 requires that branch reinforcement zones do not overlap. As a practical rule, maintain a minimum center-to-center spacing of 2x the header outside diameter between branches. For large-bore, high-pressure manifolds, perform a finite element analysis (FEA) to verify the stress distribution.

Materials

Service	Header Material	Specification
Sweet crude/gas	Carbon steel	ASTM A106 Gr. B
Sour crude/gas	Sour service CS	ASTM A106 Gr. B (NACE MR0175)
High temperature	Chrome-moly	ASTM A335 P11/P22
Corrosive service	Stainless/duplex	ASTM A312 TP316L, A790
Steam header	Carbon or alloy	A106 Gr. B or A335

Read the full guide to pipe types