Unformatted text preview: Pipeline Repair and Rehabilitation
presented by Gunavel Rathinam Regional Sales Manager T.D. Williamson Asia-Pacific Singapore 1. INTRODUCTION In light of recent government regulations, the importance of a pipeline integrity program has become a priority for pipeline asset owners. The United States Office of Pipeline Safety (OPS) published a ruling in December 2000 requiring all pipeline owners and operators to establish pipeline integrity plan. Part 195 of the Federal Register (U.S.A.) states, "... A pipeline operator must assess the integrity of the line pipe by (a) internal inspection tool or tools capable of detecting corrosion and deformation anomalies, including dents, gouges and grooves; (b) pressure test conducted in accordance with subpart E of this rule; or (c) other technology that the operator demonstrates can provide an equivalent understanding of the condition of the line pipe. The Office of Pipeline Safety must approve this method of assessing pipe integrity." The requirement goes on to say that damage to the top of the pipe must be repaired within 60 days and the pipeline operator must establish a plan for continual assessment not to exceed five years. The process of pipeline rehabilitation is part of a larger pipeline integrity management program, which every pipeline owner and operator needs to develop. Included in the pipeline integrity action plan should be the preparation, assessment and rehabilitation. But in addition, pipeline safety and security should be addressed. The potential for a pipeline to become a target for terrorism is stronger now than ever before. When considering the pipeline security, take a look at the communication system being used, how the piping system is identified and named, whether a sufficient employee/contractor identification system is in place, and if the pipeline has a remotely operated valve. 2. PIPELINE REHABILITATION / REPAIR Depending on the type of pipe damage or flaw found during the assessment phase, assortments of repair methods are available. It must first be decided that the dent, gouge or flaw is classified as an "injurious defect." This is done in the assessment stage according to the guidelines of ASME B31.8, B31.4 or one of the other pipeline codes. Generally, this means the remaining wall thickness is below the design wall thickness, that the dent or groove contains a stress-riser scratch or sharp groove or the location of the defect on the pipe or bend is detrimental to the strength of the pipe. Repair (or rehabilitation) of these defects is permissible with one of four different types of repair sleeves - welded sleeve, mechanical sleeve, Composite wraps or hot tap fitting. All four repair sleeves can provide the added reinforcement required to keep the defect from failing. The pipeline operator also may decide to remove and replace the section completely, which is the preferred repair method for long sections of pipe that are severely corroded or if a major dent or gouge is present. One way to remove and replace the dented or flawed section is to shut down the line, drain the section between valves and make the repair. This is not always an option because of the high cost of throughput loss and contractual requirements with the pipeline customers. In these cases, the operator can choose the use of Hot Tapping and STOPPLE® Plugging technology to isolate the particular section to be repaired, with the option to install a bypass piping that allows the repair to be performed onstream without interrupting the product flow. If the operator is able to stop the flow in a liquids line, he can use a freeze plug, which is a "pipeline freezing" procedure that isolates the section to be repaired with a frozen ice plug. And, similar to Hot Tapping and Stopple Plugging, this option allows the isolation of a section shorter than the distance between valves. Wall loss due to external corrosion can be dealt with by installing (or repairing) a cathodic protection system, coating repair or replacement, welded sleeves, composite sleeves or hot tap fittings. An existing cathodic protection system should be inspected and tested to determine if it is operating properly. Current outputs at stations nearest the documented external corrosion should be checked. Dried out and shrinking backfill, severed or broken lead wires, or loss of one or more anodes could be the cause of the problem. 2.1 Selection of most effective Repair / Rehabilitation methods Pipelines assessed to have excessive internal or external corrosion can be rehabilitated with : i) ii) iii) iv) v) Welded sleeve Mechanical sleeve Composite Wraps Hot tap fitting Hot tap and STOPPLE® procedure with bypass After a thorough pipeline cleaning, internal corrosion can be mitigated with an internal inhibitor coating to retard the corrosion of the internal pipe wall. This is usually applied by either a specially designed pigs called V-JET PIG or by conventional method of two pig batching procedure with the inhibitor coating material in between. The specific inhibitor is selected based on the cause of the internal corrosion. 2.1.1 Welded sleeves Welded sleeves are one of the common methods of repairing pipelines. Welding under atmospheric conditions in a dry environment was developed in the early days for pipeline tie-ins and has seen increasing use in this industry. The welded sleeve repair must be conducted in accordance with pipeline welding codes and must meet codes such as API, ASTM, and DNV, to mention a few. Welding procedures for typical pipeline materials are common and normally require a welder demonstrate their ability to perform welds that meet the code. The various types of the sleeves are : i) Sleeve halves with longitudinal weld without Backup strip ii) Sleeve halves with longitudinal weld with Backup strip and no relief groove iii) Sleeve halves with longitudinal weld with Backup strip & relief groove iv) Overlapping halves 2.1.2 Mechanical sleeve Mechanical sleeves may be installed by welding or by mechanical connectors. For onshore applications, either type is suitable. For subsea applications, only mechanical connector is suitable. Although welding on subsea pipelines is possible through the use of a special welding habitat, referred to as a hyperbaric chamber, this option is normally considered very time consuming and expensive. Hence, mechanical connectors are more often used for subsea pipeline repairs. 2.1.3 Composite Wraps Composite wraps are a permanent rehabilitation option for liquid & gas pipelines with external corrosion, gouges, arc burns and dents. Pipe temperatures can be between -20 Deg F and 180 Deg F for applying the composite wrap and can also be applied to sweating pipelines. This pipe wrap is a structural carbon fiber/epoxy composite system that utilizes a bidirectional weave of carbon filaments designed in a single ply providing superior reinforcement strength in the radial and longitudinal directions. This high strength carbon fiber and epoxy system is designed to restore your pipeline to its maximum allowable operating pressure ( MAOP ) without shutting down pipeline operation. This wraps is called “THE BLACK DIAMOND” wrap, are flexible and user friendly products for use on straight pipe or complex systems such as reducers, elbows or tees. They contain no Volatile Organic Compounds (VOC) and have minimum odor. 2.1.4. Pipeline section isolation for repair using Hot Tapping and STOPPLE® Plugging In some cases it is necessary to repair damage by cutting out the defective pipe and replacing with new, pre-tested pipe, by: i. Isolation of flow and pressure, depressurization and purging of section to be replaced ii. Hot Tapping and STOPPLE® Plugging with bypass to allow continuous flow around the isolated section of pipe Hot Tapping Hot tapping is the procedure for cutting or drilling an opening into a pipe, which is carrying product under pressure. A "hot tap" allows access to the inside of an operating pipeline without shutdown or spillage. A "hot tap" requires a fitting, a valve and a pressure-containing tapping or drilling machine. A hot tap is performed for any number of reasons, including : a. Intervene into a pipeline for maintenance and / or repair b. “Tie-in” of a new branch connection to an existing line c. Install an internal probe or monitor d. Install valves, gauges and drains on tanks e. Recover liquids from sunken ships A fitting is welded or mechanically connected to the line and an isolation valve is Installed onto the flange of the fitting. A tapping or drilling machine is installed onto the valve and the tap made through the valve. After the tap is made, the cutter is withdrawn, with the cut coupon attached, and the valve closed. If a completion plug is to be installed in the fitting, the valve can then be removed. Or, a permanent valve can be installed, which is a common practice for tie-ins. STOPPLE® Plugging After the tap is made and the tapping machine removed, a STOPPLE® Plugging Machine is installed on the valve and a plugging head inserted into the line. The plugging head, serving as a block valve, seals the line and retains pipeline pressure. If two plugging machines are used, or one plugging machine and an existing in-line valve, a section of pipe can be isolated and drained, making possible necessary repairs or modifications in the isolated section. A bypass can be installed around the isolated section, keeping the line in service. If a new section of line is being installed, it is possible to use the new section for a bypass while the old section is being removed. Completion When all repairs have been completed, the plugging heads are removed along with bypass piping (if applicable), a LOCK-O-RING (LOR) Completion plug is installed in the flange of the fitting, using the tapping machine. The LOR plug is a temporary pressure seal to allow the removal of all equipment, including the isolation valve. The LOR plug can be fitted with a scarfed nipple, which is used to weld the coupon onto the bottom of the plug, so that when the plug is installed, the coupon allows for the passage of pigs. The final step is the installation of blind flanges on all fitting flanges, which becomes the permanent pressure seal. At a future date, the blind flange can be removed, and the line re-entered, after removing the LOR Plug. Hot tapping and plugging can be performed on various types of pipe material, such as carbon steel, cast iron, concrete, stainless steel, asbestos cement and plastic. This technology can be applied on pipelines onshore and offshore, on transmission and distribution lines. Typical applications are in every industry where pressurized pipelines are in service, such as oil, gas, water, waste water, as well as in refineries, chemical plants, steel mills, nuclear power plants, paper mills and mines. Hot tapping and plugging offers many advantages : • Solve maintenance problems at minimal cost with no shutdown or spillage • Systems for use both onshore and subsea • Cost effective, onstream repair without disruption of system and operation • Performed with very little drain down or refill • No loss of expensive product • Well proven, safe and common technique 3. SUMMARY Pipeline integrity is categorized in three distinct segments - pipeline preparation, pipeline assessment and pipeline rehabilitation. Pipeline preparation defines what must be done to a pipeline before assessment and rehabilitation can take place. In most cases, this means line modification using Hottap & Stopple plugging technology, line cleaning and geometry inspection. Depending on the type of pipe damage or flaw found during the assessment phase, an assortment of repair methods is available as follows : i) Welded sleeve ii) Mechanical sleeve Composite Wraps iii) iv) Hot tap fitting Hot tap and STOPPLE® procedure with bypass v) Pipeline rehabilitation process provides operators a means to mitigate their risk of pipeline failure due to age of pipeline and third parties damages. Pipeline operators must balance cost and safety but must never error on the side of cost. Significant time and money is spent trying to determine the minimum repair cost that will provide acceptable safety. Hottap & Stopple plugging methodology offers an economical and effective alternative to other repair techniques. It offer permanent repair of damage, minimizing interruption to the operation, save money and is much less expensive than a failure. Hot Tapping & Stopple plugging technology was a mature technology with over 50 year of long history and had been widely used by major operators around the world with minimum 100,000 installations. It has been proven in service, survived critical review and is well documented. ...
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This note was uploaded on 03/12/2010 for the course MECHANICAL M768501 taught by Professor Prof.han during the Spring '10 term at Institut Teknologi Bandung.
- Spring '10