API 660 REQUIREMENTS VS TEMA
For Shell & Tube
heat exchangers employed in refineries & petrochemical complexes, the
applicability of API 660 (ISO 16812) in addition to TEMA has becoming mandatory
by most end users and consultants. API 660 lays down most requirements based on
practical considerations & past experience.
Point No. 01
Tubesheet Cladding Thickness
API 660 Requirement :
Minimum 10 mm for expanded tube to tubesheet joints. Minimum
5 mm for welded tube to tubesheet joints.
TEMA Requirement :
For TEMA Class R & B, minimum 7.8 mm for expanded tube
to tubesheet joints and 3.2 mm for welded tube to tubesheet joints.
For TEMA Class, minimum 4.8 mm for expanded tube to
tubesheet joints and 3.2 mm for welded tube to tubesheet joints.
Point No. 02
Type of Exchangers
API 660 Requirement :
TEMA types “P” (Outside packed floating head) and “W”
(Externally sealed floating tubesheet) are not allowed.
TEMA Requirement :
As per TEMA RCB-5.2, Type “P” exchangers are allowed for all
classes R, C & B.
Type “W” (Externally sealed floating tubesheet) exchangers
shall be used only for water, steam, air, lubricating oil, or similar service.
For other limitations refer TEMA.
Point No. 03
Minimum Tube OD
API 660 Requirement :
The minimum outside diameter of the tubes shall be 19.05 mm
(3/4”).
TEMA Requirement :
As per TEMA minimum tube outside diameter can be 6.4 mm also.
Point No. 04
Tube Thickness
API 660 Requirement :
Minimum tube thicknesses are defined with reference to tube
material of construction.
TEMA Requirement :
No specific guidelines (numbers) are given in TEMA for
minimum tube thickness with reference to tube material of construction
Point No. 05
Backing Device Corrosion Allowance
API 660 Requirement :
Shell side corrosion allowance shall be included on the back
side of the floating[1]head backing device
TEMA Requirement :
As per TEMA floating head backing devices are not required
to have corrosion allowance.
Point No. 06
Tubesheet Extension
API 660 Requirement :
A full-diameter stationary tubesheet shall be provided for
removable bundle exchangers with Bonnets (TEMA “B”).
TEMA Requirement :
No specific guideline is given in TEMA for consideration of
tubesheet extension.
Point No. 07
Impingement Plate Thickness
API 660 Requirement :
Minimum thickness of the impingement plate shall 6 mm
(1/4”).
TEMA Requirement :
No specific guidelines (numbers) are given in TEMA for
minimum thickness of impingement plates.
Point No. 08
Impingement Plate
API 660 Requirement :
Perforated impingement plate baffles shall not be used.
TEMA Requirement :
Use of perforated distribution device is allowed as per TEMA
recommended good practice.
Point No. 09
Baffle Thickness
API 660 Requirement :
The thickness of carbon steel or low[1]alloy
steel (max. 9 % chromium) transverse baffles and support plates shall be not
less than twice the specified shell side corrosion allowance.
TEMA Requirement :
Thickness of baffles and support plates for all materials is
given with reference to various shell diameters and plate spacing. Also as per
TEMA, baffles and support plates does not require corrosion allowance.
Point No. 10
Seal Strips Thickness
API 660 Requirement :
Minimum thickness of seal strips shall be the nominal
thickness of the transverse baffles or 6 mm (1/4”), whichever is less.
TEMA Requirement :
No specific guideline is given in TEMA for the thickness of
seal strips.
Point No. 11
Washer Requirement for Studs
API 660 Requirement :
Hardened washers shall be provided under nuts for all bolts
having diameters of 38 mm (1½”) or larger. The washers shall be at least 6 mm
(1/4”) thick.
TEMA Requirement :
No specific guideline is given in TEMA.
Point No. 12
Gasket Construction
API 660 Requirement :
Gasket construction (Welded or Non[1]welded)
is defined with respect to size and type of gaskets. Requirements for serrated
gasket, jacketed gasket, corrugated gasket, and Spiral wound gasket are
specified separately.
TEMA Requirement :
No specific guideline is given in TEMA.
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