Abstract:
An apparatus and method for copper strip corrosion testing of high vapor pressure hydrocarbon products using a dual test chamber system to provide over pressure protection to the chambers and containment of the liquid and vapor being tested.

Description:
1. FIELD OF THE INVENTION 
     The present invention relates generally to the testing of high vapor pressure fluid products for corrosive contaminates. More particularly, the present invention relates to the testing for corrosive contaminates in Liquefied Petroleum Gases (LPG), propane, natural gasoline, condensates, raw natural gas condensates and other high vapor pressure hydrocarbon products. 
     2. BACKGROUND OF THE INVENTION 
     High vapor pressure hydrocarbon products are currently tested for corrosive contaminates using ASTM D-1838—Standard Test Method for Copper Strip Corrosion by LPG or other high vapor pressure hydrocarbon products. See  FIG. 2 . This involves using a specified test cylinder with a single cavity cylinder provided with a dip tube for venting some liquid from the cylinder (to prevent excessive pressure in the cylinder whenever the liquid-filled cylinder is warmed up) and a hook for hanging a copper strip in the remaining sample of the liquid LPG product or other high vapor pressure hydrocarbon products. 
     The procedure for collecting the sample and conducting the test are carefully defined in the standard, but once the sample has been caught and a portion of the liquid has been vented to the atmosphere using the dip tube, the test basically requires the cylinder containing the remaining liquid sample and the copper strip to remain in a water bath at 100 degrees Fahrenheit for one hour. The copper strip is highly polished before being inserted into the cylinder and should remain immersed in the liquid product during the test period. 
     Following the test period, the cylinder is de-pressured, then opened, so that the copper strip can be removed and examined. The strip is graded, depending on the degree and type of discoloration, by comparing the discoloration to a comparator chart, also specified by ASTM. Number  1  copper strips are generally considered acceptable in the industry (non-corrosive), but strips graded to be number  2  or higher are generally considered to be corrosive and off-spec. 
     The prior art system and method for testing has the unacceptable feature of hydrocarbons being released to the atmosphere immediately after the liquid sample is collected in the cylinder. The purpose of the venting is to provide some outage and prevent over-pressuring a liquid-filled cylinder if the ambient temperature is warmer than the cylinder containing the sample or when the cylinder is immersed in the 100 degree Fahrenheit water bath called for by the test procedure. This is particularly dangerous if there are nearby ignition sources, but constitutes an environmental issue as well. It is also unsafe if the hydrocarbons are contaminated with hydrogen sulfide or other poisonous gases. 
     ASTM Standard D1267-12 specifies a dual chamber test apparatus. However, this is a test for vapor pressure and is not usable with the test strips needed for corrosion testing. 
     What is needed is a test apparatus and method that prevents the venting of volatile samples into the atmosphere near the point where the sample was collected, especially if the discharge is into the ambient air, near an ignition source, or near personnel (such as in refinery, terminal, pipeline installation or natural gas processing plant operating areas where the samples are usually collected). 
     Further, what is needed is a test apparatus and method that provides for the safe expansion of the hydrocarbon sample in the event the test cylinder containing the sample is warmed up by the sun or the ambient temperature after the sample is collected, or when the sample is intentionally heated in the 100 degree Fahrenheit water bath required by the copper strip corrosion test method itself. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention is an apparatus and method for copper strip corrosion testing of high vapor pressure hydrocarbon products using a dual chamber test apparatus. The test apparatus is provided with a second test chamber in fluid communication with the first chamber containing the test strip. An isolation valve is located between the first and second chamber and allows for isolating the first chamber while pulling a sample. The isolation valve is then opened to allow for expansion of the sample into the second chamber during the testing. The additional volume thus provided allows room for thermal expansion should the sample apparatus be warmed during the testing process, as is the usual case. The second chamber may also be equipped with a pressure gauge and/or a purge valve. The entire apparatus must be fully designed to handle the operating conditions and fluids to be encountered during its intended use. 
     The present invention will prevent over pressuring of the test apparatus and does not require venting sample to the atmosphere near the point of sampling, which is a routine practice with the current sampling method in ASTM D-1838. In extreme cases, over pressure can cause injury of workers and property damage. Uncontrolled venting always constitutes an environmental concern. 
     The present invention also allows any necessary venting of product to the atmosphere to occur after the testing is complete and to be performed in a safe location, typically via a vent or vapor recovery system designed to handle such products. Venting near the point of sampling is not required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The preferred embodiment of the invention has been described. Other features, aspects, and advantages of the present invention will become better understood with regard to the following appended claims, and accompanying drawings (which are not to scale) where: 
         FIG. 1  is a diagram of the preferred embodiment of the present invention; and 
         FIG. 2  is the ASTM specification for the prior art copper strip corrosion test of high vapor pressure hydrocarbon products. 
     
    
    
     DETAILED DESCRIPTION 
     The test apparatus  10  of the present invention uses a first chamber  12  and a second chamber  14  in fluid communication with each other. An isolation valve  16  is located between the first chamber  12  and second chamber  14 . The isolation valve  16  is capable of isolating the first chamber  12  from the second chamber  14  or allowing free fluid communication between the first and second chambers  12  and  14 . See  FIG. 1 . In the preferred embodiment the first chamber  12  has an inlet valve  18  for filling the interior  20  of the first chamber  12  with liquid LPG or other high vapor pressure hydrocarbon products. It also contains a means for inserting, hanging and removing copper strips, and a means for cleaning and purging the cylinder. 
     The preferred embodiment includes a removable cap  22  which threadedly engages with the first chamber  12 . When the cap  22  is removed, it provides access to the interior  20  of the first chamber  12  for installing a test strip  28  as well as cleaning and purging the first chamber  12 . There is a rod  24  with a hook  26  which extends from the removable cap  22 . The hook  26  is sized and located to receive a test strip  28  and to properly suspend the test strip  28  in the liquid phase of the sample in the first chamber  12  after the sample is collected. Further, the inlet valve  18  may be mounted in the removable cap  22 . 
     The second chamber  14  has an empty interior  30  with provisions for cleaning and purging. In the preferred embodiment, there is a purge valve  32  in fluid communication with the second chamber  14 , such that it is capable of isolating the second chamber  14  from atmosphere. A second chamber  14  may also be equipped with a pressure gauge  34 . The pressure gauge  34  measures and displays the pressure in the second chamber  14 . 
     In the preferred embodiment, the interior  20  of first chamber  12  accounts for approximately 70% of the total volume of the test apparatus  10 . The interior  30  of the second chamber  14  provides 30% of the total volume of the test apparatus  10 . 
     The method for testing includes the steps of removing the removable cap  22  from the test apparatus  10 . Placing a properly prepared test strip  28  on the hook  26 . Placing the rod  24 , hook  26  and test strip  28  in the first chamber  12 . Installing the removable cap  22  on the test apparatus  10 . 
     When collecting a sample, the completely empty and internally clean apparatus (or containing only a very low pressure residue of a clean inert gas such as helium) will have the inlet valve  18  connected to the sample source using appropriate connecting fittings and hoses or tubing (typically stainless steel). Prior to opening the inlet valve  18 , the person collecting the sample must ensure the isolation valve  16  between chamber  12  and chamber  14  is closed and the purge valve  32  is also closed. Once the first chamber  12  is filled with sample, the inlet valve  18  should be closed and the test apparatus  10  must be safely disconnected from the sample source. Note that the purge valve  32  from second chamber  14  should be verified to be in the closed position up to this point and that no leaks are present anywhere in the test apparatus  10 . At this point, the first chamber  12  should be full of product and the second chamber  14  is still empty (unless a very low pressure inert gas is intentionally left in the cylinder). The person collecting the product sample can now open the isolation valve  16  to allow some of the sample in the first chamber  12  to flow into and fill the second chamber  14 , providing adequate volume for thermal expansion anticipated during the test procedure (with a water bath heating the apparatus to 100 degrees F.). It is important to the test to be sure the test strip  28  is still suspended in the liquid phase of the sample in the first chamber  12  during the one hour test period in the water bath specified in the ASTM test procedure. The pressure gauge  34  in the second chamber  14  will help ensure the sample is allowed to expand into the previously empty second chamber  14  by showing that the second chamber  14  is in fact de-pressured and empty until the product in the liquid-filled first chamber  12  is intentionally allowed to expand into the second chamber  14 . 
     The test method then requires warming the sample and test apparatus  10  to 100 degrees Fahrenheit in a water bath. Maintaining the sample at 100 degrees Fahrenheit for 1 hour. Releasing the sample from the test apparatus  10  by opening the inlet valve  18  or the purge valve  32 . In some situations, the sample may be released into the atmosphere. However, in the preferred embodiment, the purge valve  32  will be connected to an exhaust system and the sample is removed in an environmentally friendly and safe manner, typically into a laboratory vent system or a vapor recovery system intended for this type of service. The test strip  28  is then removed from the first chamber  12  and examined for test results using the current ASTM test criteria. The test strip  28  is removed by removing the removable cap  22  from the first chamber  12 . 
     Opening the isolation valve  16  during the process above prevents the possibility of over-pressuring the first chamber  12  due to warming the sample and test apparatus  10  when ambient conditions are warmer than the temperature of the fluid and apparatus. Not only does the addition of the second chamber  14  prevent over-pressuring of the first chamber  12 , it also prevents any vapors from escaping to the atmosphere in a hazardous environment where the sample is collected, such as in the process area of a refinery or gas processing plant. The sample and apparatus can be transported safely to a lab and the test run in a safe environment, which is typically provided with a safe and environmentally friendlier system when the apparatus is depressured and opened to examine the test strip  28 . 
     The foregoing description details certain preferred embodiments of the present invention and describes the best mode contemplated. It will be appreciated, however, that changes may be made in the details of construction and the configuration of components without departing from the spirit and scope of the disclosure. Therefore, the description provided herein is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined by the following claims and the full range of equivalency to which each element thereof is entitled.