API MPMS 19.3B:1997(R2002) pdf download.Manual of Petroleum Measurement Standards Chapter 19.3- Evaporative Los Measurement
1 Scope
This test method may be used to establish evaporative rim- seal loss factors for rim seals used on external and internal floating-roof tanks. The test method involves passing a con- trolled flow rate of air through a test chamber that contains a test liquid and a test rim seal, and measuring the concentra- tion of the test liquid vapor in the air streams entering and leaving the test chamber. 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 measured 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.
4 Summary of Test Method
The test method described in this standard uses a mass bal- ance procedure to measure a rate of evaporative loss. A test chamber is ftted with a test rim seal. Spacers are placed between the test rim seal and the simulated tank shell of the test chamber to create a specified rim-seal gap area. The area below the test rim seal is flled to an appropriate height with a volatile hydrocarbon test liquid of known properties, such as normal-hexane or isohexane. A prescribed level of air flow rate through the test chamber is set. The concentration of the test liquid vapors in the air is measured at the test chamber inlet and outlet. A mass balance is then used to determine the loss rate of the volatile hydrocarbon test liquid vapor through the rim seal. The loss rate is then factored for the properties of the test liquid and the length of the test rim seal in order to determine an evaporative rim-seal loss factor for the test rim seal at that seal gap area.
5 Significance and Use
This test method establishes a procedure for measuring the evaporative rim-seal loss factor of rim seals that are used on external, covered, and internal floating-roof tanks. The testing is to be performed in a laboratory that has been approved by the API for this purpose, in accordance with the API Manual of Petroleum Measurement Standards, Chapter 19.3, Part G, “Certified Loss Factor Testing Laboratory Registration.” The values determined by this method are to be evaluated in accordance with the API Manual of Petroleum Measurement Standards, Chapter 19.3, Part F,“Evaporative Loss Factor for Storage Tanks Certifcation Program” in order to assign API- certified loss factors to the particular rim seal tested. The lab- oratory approval procedure, the test method, and the evalua- tion method together constitute a procedure by which manufacturers of floating-roof rim seals may obtain API-cer- tifed loss factors for rim seals of their proprietary design.