API MPMS 19.3C:1998(R2002) pdf download.Manual of Petroleum Measurement Standards Chapter 1 9.3- Evaporative Loss Measurement
1 Scope
This test method may be used to establish evaporative rim- seal loss factors for rim seals used on intermal floating-roof tanks. The test method involves measuring the weight loss of a test assembly over time. This standard specifies the test apparatus, the instruments, the test procedure, and the calcu- lation procedures to be used. The variables that are to be mea- sured are defined, and quality provisions are stipulated. The format for reporting the values of both the test results and their associated uncertainty are also specified. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the respon- sibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2 Normative References
The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the pos- sibility of applying the most recent editions of the standards indicated below.
3.2.4 Rim-Seal Loss Factors
The unit of reporting rim- seal loss factors is the pound-mole per foot of tank diameter per year, designated lb-mole/ft yr. The units of the rim-seal loss factor, Kr, do not actually indicate pound-moles of vapor loss over time, but rather are units of a factor that must be multiplied by the tank diameter and other factors (which are dimensionless) to determine the actual pound-moles of evaporative loss over time for a given liquid product. To convert the pound-mole per foot of tank diameter per year units of the rim-seal loss factor to a loss rate in terms of actual pound-moles per foot of tank diameter per year, the rim-seal loss factor, Kn is multiplied by the dimen- sionless coefficients P*, which is a function of the product vapor pressure and atmospheric pressure, and Kc, the product factor. A pound-mole, designated lb-mole, is an amount of a sub- stance the mass of which, when expressed in pounds, is equal to the numerical value of the molecular weight of the sub- stance. To then convert the actual pound-moles per foot of tank diameter per year to pounds per year of a given liquid product, the loss rate (K,P*Kd) is multiplied by the tank diameter, D, and the molecular weight of the liquid product in its vapor phase, Mv with molecular weight having units of pounds per pound-mole. Additional information on this for- mula may be found in API Publications 2517 and 2519, and in API MPMS, Chapter 19.2.