What Is a Heat Exchanger? Shell and Tube

A heat exchanger is a device that transfers thermal energy between two or more fluids at different temperatures without mixing them. In oil and gas processing, heat exchangers are used to heat, cool, condense, or vaporize process streams. The shell-and-tube heat exchanger is the most common type in the industry, accounting for the majority of heat transfer equipment in refineries, gas plants, and petrochemical facilities.

Heat exchangers are classified as pressure vessels and are designed to ASME Section VIII and TEMA (Tubular Exchanger Manufacturers Association) standards.

Heat Exchanger Types and Applications

Type	Construction	Best For
Shell and tube	Bundle of tubes inside a cylindrical shell; one fluid flows through tubes, the other over the tube bundle	High pressure, high temperature, fouling services
Plate (gasketed)	Corrugated plates with gaskets; fluids flow in alternating channels	Clean services, moderate pressure, easy maintenance
Plate and frame (welded)	Welded plate packs without gaskets	Aggressive fluids, higher pressure than gasketed plates
Air-cooled (fin-fan)	Finned tube bundles with forced-draft fans; ambient air as cooling medium	Where cooling water is unavailable or expensive
Double pipe	Pipe-in-pipe; one fluid in inner pipe, the other in annulus	Small duties, high pressure, simple design
Spiral	Two curved plates forming spiral channels	Slurries, high-fouling fluids

TEMA Designations

Shell-and-tube exchangers are classified by a three-letter TEMA code describing the front head, shell, and rear head types:

Position	Common Types	Description
Front head	A (channel with removable cover), B (bonnet—integral cover)	Defines how tube-side access is provided
Shell	E (single pass), F (two-pass with longitudinal baffle), J (divided flow), X (crossflow)	Defines shell-side flow pattern
Rear head	L (fixed tubesheet), S (floating head), U (U-tube bundle)	Defines how differential thermal expansion is handled

A common designation is BEM (bonnet, single-pass shell, fixed tubesheet) for simple duties, or AES (channel, single-pass shell, floating head) for services requiring bundle removal and cleaning.

Common Mistake

Specifying a fixed-tubesheet exchanger (TEMA L or M rear head) when the temperature difference between shell-side and tube-side fluids exceeds approximately 50 degrees C can cause excessive thermal stress at the tubesheet. Use a floating head (S or T) or U-tube (U) design for large differential temperatures to allow independent expansion of the shell and tubes.

Key Design Parameters

Parameter	Typical Specification
Design code	ASME VIII Div.1 + TEMA Class R (refinery), C (commercial), B (chemical)
Tube OD	19.05 mm (3/4”) or 25.4 mm (1”) most common
Tube material	Carbon steel, stainless steel, duplex, titanium, Cu-Ni alloys
Shell material	SA-516 Gr.70 (carbon steel), SA-240 (stainless)
Baffle type	Segmental (single or double), disc-and-doughnut, helical
Fouling factor	0.00017 to 0.00035 m2K/W (depends on service)

Heat exchangers are critical components in virtually all oil and gas facilities, from crude preheat trains in refineries to gas cooling in upstream production.

Read the full guide to oil and gas equipment