New 1998 Boiler Performance Test Code

PTC 4.1 issued in 1964 and reaffirmed in 1991 was superseded and withdrawn in 1998 to be replaced by a new code PTC 4 that corrects many deficiencies of PTC 4.1 and makes the testing more accurate. However, PTC 4.1 in many parts of the world continues to be fol­lowed. Table 1.7 shows the essential differences between the two codes.

Even if the test uncertainty is eliminated and the tests are performed with the same type of instruments to the same levels of accuracy, the results of the tests conducted by the two methods would marginally vary. This is, first of all, because of slight differences in fuel efficiency as per PTC 4 and gross efficiency as per PTC 4.1 in the way the heat credits are treated. PTC 4 defines the reference temperature, makes heat credit accounting compul­sory, and adopts certain minor improvements in the calculation methods. PTC 4 is, on the whole, a more comprehensive test code based on modern measurement, data reduction, and calculation with uncertainty analysis included and is therefore superior to PTC 4.1. There are certain differences in the estimation of loss and credits between the two codes as shown in Table 1.8.

Performance Test

Performance Test


Codes (PTC) 4.1

Codes (PTC) 4


Gross versus

100 — (heat loss/fuel

100 — (heat loss — heat

Fuel efficiency replaces gross

Fuel efficiency

Input + heat credits) %

Credits/fuel input) %

Efficiency of PTC 4.1; fuel flow is directly calculable


Not considered

Uncertainty values

Mainly driven by economical


Listed in 1.3-1 and level to be agreed

Instrumentation and data sampling procedures chosen; Section 4 of PTC 4 provides background and guidance

Radiation and

ABMA radiation loss

Losses are accurately


Curve to be used

Evaluated; ABMA


Curve not used


Usually ambient; heat

25°C to be adopted and

With a fixed reference


Credits can be

Heat credits and loss

Temperature, all results are on


Are calculated

The same basis and are directly comparable


Energy absorbed by working fluid

Energy absorbed by working fluid that is not recovered within steam generator envelope; for example, steam to SCAPH


Better covered

Test objectives or performance parameters


Better defined

Corrections to design conditions

Flue gas

Based on measured O2 and CO2

Based on measured O2, both wet and dry

For efficiency calculations

Calculation of

Specific heat


In PTC 4, the enthalpies of dry

Losses and

Air, dry flue gas, moisture


Vapor, and fuels are defined by equations (curve fits)

Fuel analysis

Mass basis

Conversion from volumetric to mass is also provided


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