Economic benefits of valve commissioning during construction.
As a result of the focus brought to the problem of damaged valve seals many pipeline operators and construction contractors have amended their construction procedures and Sealweld new valve commissioning procedures have evolved to become a "best practice" for many pipeline operators around the world.
Learning from past and present experience commissioning new valves over thousands of miles of new pipeline construction, Sealweld has developed additional procedures and refined others, including the use of the inside-out air set test and the valve body jumper assembly.
The Inside-Out Air Seat Test
The inside-out air seat test is a simple yet effective method of verifying valve seal integrity. To explain, with the valve in the full open or full closed position, low pressure air is induced into the body cavity of the valve, the air inlet valve is closed and the technician watches the pressure gauge on the air test assembly to verify that the body cavity pressure is holding. The test only takes a few minutes to perform.
This simple test should be performed:
* Upon receipt of the valve (this establishes the base-line data).
* After welding the valve into an assembly or into the pipeline.
* after hydro-testing.
* after pigging operations.
* every time the valve is handled and/or cycled.
* after line purge and the initial line fill.
* as a component of the final handover documentation.
Most importantly, by performing the test at regular intervals throughout the construction and commissioning process--if any of the many contractors are found to be performing procedures that result in valve seal damage, these can be identified immediately and corrected before any more valves are damaged in a similar manner.
Previously--the pipeline operator would only discover the seal damage after pipeline start-up and the blame game would begin.
The data obtained from the air seat test can be used to resolve insurance claims, warranty disputes and as a means of finalizing the pipeline handover from the contractor to the pipeline operator.
Valve manufacturers have also discovered the benefits of recommending new valve commissioning procedures. Instead of having to respond to their customers attempts at warranty claims due to valve seal leakage (which are not covered under the manufacturing defect clause) their customers are satisfied in the knowledge that every valve seals perfectly at start up.
The Valve Body Jumper Assembly
Another simple yet effective procedure is the use of valve body jumper assemblies during hydrostatic testing of valve assembles and pipelines.
To explain, the pipeline is hydrostatically tested to 1.5 x MOP and the valves must be cycled to the 1/2 closed position to equalize the high test pressure within the valve body cavity. For large-diameter block valves, in order to cycle the valve the power actuator must be installed and working or a manual gear set must be installed to cycle the valve. This is not always possible during the initial stages of construction due to the lack of power gas or electricity to the valve site.
Valve seals are most vulnerable during construction because that is when the most debris is in the pipeline. Cycling the valve against this debris in a "dry" condition creates scratches and cuts to the soft seals and critical sealing surfaces. The risk of this type of damage can be greatly reduced by not cycling the valve.
The body jumper assembly is simply a hose and valve assembly that connects the body cavity of the valve with the pipeline being hydrostatically tested. As the pipeline is filled with water, the body cavity is also filled. As the test pressure in the pipeline is gradually brought up to full test pressure, the pressure in the body cavity is also brought up to the same test pressure, thus eliminating any risk of a pressure differential.
The valve technician will ensure that all of the hose and valve connections are properly made up to eliminate the risk of leakage and a failed hydrostatic test. The valve technician will also inspect for valve stem leakage, valve body leakage, valve fitting leakage during the pipeline hydrostatic test.
Another critical consideration is venting the air pocket out of the top of the valve body during the hydrostatic test and in liquids pipelines at start-up. Air pockets will normally collect at the high points along the pipeline; this usually means the upper part of the valve body cavity, especially in gate valves.
Because the air is compressible this can give inconsistencies and/or erroneous data in the hydrostatic test report. The air pocket can also result in the seat rings not making proper contact with the ball or gate resulting in a false indication of valve seal damage. This can usually be accomplished by removing a threaded plug in the upper section of the valve. When the threaded plug is replaced the thread seal can be re-verified during the pipeline hydrostatic test.
Upon the completion of a successful hydrostatic test of the pipeline the test pressure can be reduced down to the MOP in order to verify valve seal integrity. This only takes a few minutes and provides an accurate indication of valve seal integrity at normal operating pressure of the pipeline.
These are only a few examples of the ongoing changes to valve commissioning procedures. These procedures are under perpetual improvement and are modified to suit the different construction practices and techniques on new pipelines around the world.
Training Field Personnel
Sealweld Corporation, in association with SAIT Polytechnic, has created the ValvePro--Valve Technician Certification Program. The training program consists of computer based self-study via CD-ROM or Internet Web-based learning, which is combined with instructorled classroom training with an emphasis on hands-on task competency testing.
The ValvePro program includes lessons on all of the basic skills a valve technician requires to safely perform routine valve maintenance inline and under pressure. This includes dangerous valve fitting identification, high-pressure sealant injection gun and pump operation and maintenance, specific procedures for performing a valve site survey, routine valve maintenance procedures and basic valve sealing procedures. ValvePro Level 2 introduces new valve commissioning and includes procedures. To learn more go to www.valvepro.com
By Dean Chisholm, President, Sealweld Corporation, Calgary, Alberta, Canada
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|Title Annotation:||Tech Notes: Product Development|
|Comment:||Economic benefits of valve commissioning during construction.(Tech Notes: Product Development)|
|Publication:||Pipeline & Gas Journal|
|Date:||Aug 1, 2007|
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