Nonetheless, over the years closed sampling equipment has improved, and some third-party companies now manufacture closed sampling equipment that has the capability to draw a sample that can be used for vapour pressure. This device allows for a running sample to be taken, and for the actual sampling tube to be removed from the sampling device and taken to the laboratory for testing. This results in needing a separate sampling tube for the sampling of each individual tank.
Additionally, the primary sample collector / container is an integral part of the sampling device, and it is not possible to detach this and allow the sample to be transported to the laboratory in the primary container. Many of these units require the sample to be decanted into the housing and then transferred to a secondary container, which is also not acceptable.
11.2 Sampling for Hydrogen Sulphide (H 2 S) Analysis Sampling for Hydrogen Sulphide (H 2 S) analysis is a specialized sampling application in the same way that sampling for vapour pressure analysis is. It is necessary to review the test method that will be used to perform the analysis to determine the actual sampling requirements. Almost all of these specialized requirements have to do with sample handling. In the main, samples are taken as specified in the usual manual sampling standards (API MPMS Ch. 8.1, ASTM D 4057 and ISO 3170) or the usual automatic sampling standards (API MPMS Ch. 8.2, ASTM D 4177 and ISO 3171). There are three more commonly used analytical test methods to test for H 2 S; however, these are not the only possible methods. Additionally, methods are constantly being updated and new methods are also added from time to
Some closed system samplers do not have the capability to take a running or all-levels sample.
As Vapour pressure is usually a critical specification that is often tested prior to acceptance of the cargo it is very important that we advise the client of the limitations of these devices where applicable so that alternative sampling methods can be agreed to, periodic spot line samples may be an alternative. If spot line samples are taken, a tap extender must be used so that the sample container can fill from the bottom, as shown in the below image.
11.1.4 Sample Handling
Prior to taking the sample, and where possible cool the sample bottles by immersing them in the product and then emptying the bottle back into the tank. This also rinses the bottle with the product to help ensure contaminants are removed.
• Running samples should be between 70% and 85% full when withdrawn from the tank
• Immediately cap the bottle and invert it.
time, so this review is not meant to be a substitution for reviewing the test methods themselves.
• If the bottle is greater than 85% full, discard the sample and take another one. • It is common practice to place inverted Vapour pressure samples in ice, which is carried in a cooler. • It is possible to use metal cans, provided that the sample is taken in the can and the cap can make a Vapour tight seal
The three methods in question are:
• ASTM D 5705 - Standard Test Method for Measurement of Hydrogen Sulfide in the Vapour Phase Above Residual Fuel Oils.
• Plastic bottles are not permitted
72
Made with FlippingBook Annual report maker