Calculating losses from steam traps

UNFCCC classification and loss computation based on working status

As per the United Nations Framework Convention on Climate Change (UNFCCC) steam traps can be classified as follows based on their working status.

Table: UNFCCC Steam trap classification based on working status

TerminologyDescriptionDefinition
OKGood TrapTrap in normal operating mode
BTBlow throughTrap has failed in an open mode with
maximum steam loss
LKLeakingTrap has failed in a partially open mode with a
steam loss of approximately 25% of maximum
RCRapid cyclingDisc trap going into failure mode
PLPluggedTrap has failed in a closed position
and is backing up condensate
FLFloodedTrap is assumed to be undersized and
unable to handle the condensate load
OSOut of serviceThe steam supply line is off and the trap
is not in service
NTNot testedTrap in service but not tested due
to inaccessibility

Computing steam loss through leaking steam traps

The United Nations Framework Convention on Climate Change (UNFCCC) has defined a methodology to compute the loss through leaking traps.

Type of failureFT ty
Blow-thru (BT)1
Leaking (LK)0.25
Rapid cycling (RC)0.2

The service factor “FT ty” takes into account that the steam loss depends on the trap size (orifice) in relation to the actual load, which differs based on applications. This value can be determined from the table below

ApplicationService Factor FS ty
Process steam traps0.9
Mainline and tracer steam traps1.4

Steam losses also depend on the actual size of the orifice. The flow coefficient “CV t,y.” is a function of the orifice size (in inches).

CVt,y= 22.1 × D²
Where D² is the diameter of the orifice in inches