What Is a Pipe Rack? Design and Types

A pipe rack is an elevated steel structure designed to support and route process piping, electrical cable trays, and instrument cable runs between equipment in industrial facilities such as refineries, petrochemical plants, and LNG terminals. Pipe racks form the primary routing corridors (or “pipe alleys”) within a plant and are one of the largest structural steel items in any EPC project.

Pipe Rack Types

Pipe racks are classified by their structural configuration and the number of tiers (levels) they support:

Type	Description	Typical Application
Single-tier	One level of pipe supports on transverse beams	Small facilities, single pipe routes
Double-tier	Two levels; pipes on top, cable trays below (or vice versa)	Most common configuration in process plants
Multi-tier	Three or more levels stacked vertically	Large refineries, LNG plants with dense routing
T-type	Main rack with perpendicular branch racks	Routing to individual equipment items
Modular/pre-assembled	Factory-fabricated rack modules shipped to site	Offshore platforms, remote locations, fast-track projects
Pipe bridge	Long-span structure crossing roads, railways, or waterways	Between plant areas or over access roads

Structural Design Criteria

Pipe rack design follows structural steel codes (AISC, Eurocode 3, or IS 800) and is governed by the following load cases:

Load Category	Description	Standard
Dead load (D)	Self-weight of steel structure	ASCE 7 / EN 1991
Pipe operating load	Weight of pipes filled with operating fluid	Process data
Hydrotest load	Weight of pipes filled with water during hydrostatic testing	ASME B31.3
Thermal load	Pipe expansion and contraction forces transferred to supports	Stress analysis output
Wind load (W)	Lateral force on structure and piping per wind code	ASCE 7 / EN 1991-1-4
Seismic load (E)	Lateral force per seismic zone classification	ASCE 7 / EN 1998
Cable tray load	Weight of electrical and instrument cable trays	Electrical design
Live/maintenance load	Personnel access, maintenance platforms	Typically 2.0-2.5 kN/m2

Pro Tip

The hydrotest load case (pipes filled with water) is often the governing design condition for pipe rack beams, since water is significantly heavier than most process fluids. Always check hydrotest vs. operating load to size the beams correctly.

Typical Dimensions and Span Lengths

Parameter	Typical Range	Notes
Span (column spacing)	6 m to 9 m (20 to 30 ft)	6 m is standard; 9 m for lighter loads
Bay width (transverse)	4 m to 8 m (13 to 26 ft)	Depends on number of pipe rows
Tier height (clear)	2.5 m to 3.5 m (8 to 12 ft)	Minimum clearance for access and maintenance
Bottom tier elevation	4 m to 5.5 m (13 to 18 ft) above grade	To allow vehicle and pedestrian passage
Column sections	W-shapes (HEA/HEB) or built-up box sections	HEA/HEB beams are common
Transverse beams	W-shapes or built-up plate girders	Sized for hydrotest load
Bracing	X-bracing or V-bracing in vertical and horizontal planes	Every 3-5 bays

Materials

Pipe rack structural steel is typically specified as:

Component	Material Grade	Specification
Columns	S235/S275/S355 (EU) or A36/A572 Gr.50 (US)	EN 10025 / ASTM A36/A572
Beams	S235/S275/S355 or A36/A572 Gr.50	EN 10025 / ASTM A36/A572
Bracing	Angles, channels, or HSS sections	EN 10210 / ASTM A500
Base plates	Steel plates S235/S275 or A36	EN 10025 / ASTM A36
Bolts	Grade 8.8 or A325	EN 14399 / ASTM A325
Hot-dip galvanizing	For offshore or coastal environments	ISO 1461 / ASTM A123

Surface protection for onshore racks typically involves a multi-coat paint system (primer + intermediate + topcoat). Offshore pipe racks use hot-dip galvanized steel or duplex coating systems (galvanizing + paint).

Design Process

The pipe rack design workflow in an EPC project follows this sequence:

1. Plot plan / layout: Piping layout engineers define the routing corridors and pipe rack centerlines on the plot plan
2. Pipe stress analysis: Stress engineers calculate thermal expansion forces and identify support types (pipe shoes, anchors, guides)
3. Load tabulation: Piping group provides dead loads, operating loads, and hydrotest loads per support point
4. Structural analysis: Structural engineers model the rack in FEA software, apply all load combinations, and size members
5. Connection design: Beam-to-column connections, base plate design, and anchor bolt sizing
6. Fabrication drawings: Detailed shop drawings for steel fabrication and pipe support attachment details

Common Mistake

Undersizing transverse beams for the hydrotest load case is a frequent design error. During commissioning, all pipes on a rack level may be hydrotested simultaneously, creating loads 30-50% higher than the operating case.

Pipe racks account for a significant portion of structural steel tonnage in a plant (often 15-25% of total steelwork). Efficient rack design reduces both material cost and erection time.

Read the full guide to steel plates