ADVANCEMENTS IN MECHANICAL SEALING

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ADVANCEMENTS IN MECHANICAL SEALING - API 682 FOURTH EDITION

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<ul><li><p>Page 1 Copyright 2015 by Turbomachinery Laboratory, Texas A&amp;M Engineering Experiment Station </p><p>ADVANCEMENTS IN MECHANICAL SEALING - API 682 FOURTH EDITION Michael B. Huebner Flowserve Corporation Deer Park, TX, USA </p><p>Gordon S. Buck John Crane Inc. Baton Rouge, LA, USA </p><p>Henri V. Azibert Fluid Sealing Association Wayne, PA USA </p><p> ABSTRACT </p><p> API 682 is the leading document for </p><p>mechanical seals in petrochemical, chemical, and pipeline services worldwide. It has combined the aspects of seal design, testing, standardization, and applications to provide the users and OEMs alike with a common source of information for mechanical seals. As seal technology has advanced, the standard has expanded to incorporate new seal designs, materials, seal selection guidance, and piping plans. The current edition, the Fourth Edition, was published in May of 2014 and is now available for purchase. This tutorial will cover the major changes introduced in the Fourth Edition. </p><p> HISTORY OF API 682 </p><p> Mechanical seals have been accepted as the </p><p>standard method for sealing rotating pumps for many years. While some mechanical seal standard existed, they were generally buried in other standards such as DIN 24960, ANSI B73 and API 610. All of these standards were primarily pump standards and any seal references were directed at how mechanical seals would interact with the referenced pumps. </p><p> In the late 1980s a group of refinery </p><p>equipment engineers and managers began to compare sealing solutions in refinery applications. This group, led by V. R. Dodd of Chevron, came up with a general plan and the American Petroleum Institute (API; Washington, D.C.) agreed to establish a standard for mechanical seals: API 682. A Task Force was formed in 1990 and the first meeting was held in January 1991. This Task Force was comprised of fourteen members from various refineries, seal and pump manufacturers. As part of the process in developing the standard, the Task Force created standard definitions for concepts such as seal types, seal arrangements, and seal qualification tests. API 682, First Edition, was published in October 1994. </p><p> API 682 First Edition was one of the most </p><p>successful standards in APIs history with sales in over 25 countries. While the First Edition Task </p><p>Force had in effect created a standard that was used throughout the world, they had not authored an international standard. In order to gain international acceptance, the American Petroleum Institute opened up the standards development process to global input from the International Organization for Standardization (ISO; Geneva, Switzerland). </p><p> In addition to international review, the </p><p>Second Edition introduced the concept of seal categories and new seal designs such as gas seals and containment seals. Additional options for seal configurations and orientations (such as dual face-to-face and back-to-back) were added. The scope of the standard was also broadened to include seals for chemical duty pumps. In the process new piping plans and test qualification procedures were developed to cover the new scope. The Second Edition of API 682 was confirmed by the international community as ISO-21049 in 2002 with only minor changes from API 682 Second Edition. To completely align API 682 and ISO 21049, API 682 Third Edition was issued in 2004. </p><p> Since the publication of the Third Edition, </p><p>seal technology has continued to advance. End users and OEMs have made recommendations to expand the scope so that the benefits of the standards could be applied to new applications and new seal designs. Improvements in piping plans have made seal installations more reliable. New seal selection concepts have been developed. The API 682 Task Force worked to incorporate the industry needs and new technology into the new standard. The resulting work, API 682 Fourth Edition continues the tradition as the leading standard for mechanical sealing. Recently, the American Petroleum Institute has moved to issue its standards independently of the ISO standards organization. For this reason, the next edition of API 682 will only be issued as API 682 Fourth Edition and not as ISO 21049. </p><p> OVERVIEW OF FIRST EDITION </p><p>The mission statement for the First Edition Task Force was captured in the first section of the standard: </p><p> 3rd Middle East Turbomachinery Symposium (METS III) 15-18 February 2015 | Doha, Qatar | mets.tamu.edu </p></li><li><p>Page 2 Copyright 2015 by Turbomachinery Laboratory, Texas A&amp;M Engineering Experiment Station </p><p>This standard is designed to default to the equipment types most commonly supplied that have </p><p>a high probability of meeting the objective of at least three years of uninterrupted service while </p><p>complying with emissions regulations. </p><p> Although this mission statement no longer </p><p>appears in the standard, it is important to realize its impact not only on First Edition but on subsequent editions. There were several key assumptions made by the First Edition Task Force in meeting this goal. </p><p> address 90% of the applications in a </p><p>typical refinery address a limited range of shaft sizes and </p><p>operating conditions default to one solution. </p><p> The First Edition of API 682 was filled not </p><p>only with the technical details normally associated with a standard but also with a thorough explanation of how seals should be applied and the background behind many of the requirements of the standard. The document contained notes and comments that gave the reader an insight into the Task Forces reasoning behind many of the requirements. Originally, these notes and comments were intended only for the Task Force; however, the reviewers of the draft standard asked that they be kept in the finished document. Some comments were expanded to become tutorials and were moved to the appendix. </p><p> The First Edition also provided a seal </p><p>selection guide for a number of typical refinery applications. Before this could be done, it was necessary to categorize refinery applications into a number of services: Non-hydrocarbon, Non-flashing hydrocarbon, and Flashing hydrocarbon. </p><p> In order to formulate the selection guide, it </p><p>was also necessary to categorize the many different types of seals that were used in refinery services. Three seal types, A, B, and C, were designated to cover pusher seals, bellows seals, and high temperature seals respectively. </p><p> Prior to First Edition, multiple seals were </p><p>designated as being either tandem or double seals; however, advances in seal design had rendered these classic terms obsolete. As a result, there was some confusion on how multiple seals </p><p>were designated. The Task Force decided to use a more descriptive designation and chose to define dual seal arrangements. A dual seal would be two mechanical seals used in the same seal chamber. The fluid between these two seals could be either pressurized or unpressurized. Three standard arrangements were defined: Arrangement 1 would be a single seal, Arrangement 2 would be a dual unpressurized seal, and Arrangement 3 would be a dual pressurized seal. </p><p> End users wanted assurances that the seals </p><p>offered by the OEMs were capable of meeting the API 682 goals when run under actual conditions. The only way to do this was to require seal performance testing, termed Qualification Testing, on process fluids under representative pressures and temperatures. The goal of the qualification test was to simulate a long-term steady state run followed by a process upset. The simulated process upset consisted of pressure changes, temperature changes and included loss of flush. Five fluids were selected for the qualification tests: water, propane, 20% NaOH, cold oil and hot oil. These five fluids included a wide range of viscosity, vapor pressure, specific gravity, specific heat and atmospheric boiling point. In addition, there were actually three other "test fluids" -- the buffer/barrier fluids: glycol/water, diesel, and low viscosity oil. </p><p> API requires a periodic review of its </p><p>standards and as sealing technology evolved it became apparent that API 682 First Edition should be updated. </p><p> OVERVIEW OF SECOND AND THIRD EDITIONS </p><p> After the release of API 682 First Edition, gas </p><p>seals and dry running containment seals became more common in many industries. New piping plans for gas seal control panels and containment seals were necessarily required and developed. In addition, many users and manufacturers wanted to expand the scope of seal configurations and orientations that had been specified by First Edition. </p><p> Another criticism of API 682 First Edition </p><p>was that it considered only API 610 pumps and only refinery applications. The chemical and petrochemical industries routinely use ASME pumps in addition to API 610 pumps. Broadening the scope of pumps covered by API 682 would </p></li><li><p>Page 3 Copyright 2015 by Turbomachinery Laboratory, Texas A&amp;M Engineering Experiment Station </p><p>allow standardized seals to be applied in a greater number of industries. </p><p> The First Edition was written from the </p><p>perspective of refinery applications and focused on heavy duty pumps and seal designs. Since the standard was being applied to other industries, users recognized the need to select seals according to the severity of the application. This need was met by defining seal categories. There are three categories: Category 1, 2, and 3. Category 1 seals were largely intended for non-API-610 pumps. Category 2 seals were intended for API 610 pumps. Category 3 seals were also intended for API-610 pumps and were essentially the same as the original API 682 First Edition seals. </p><p> The Task Force also recognized that not all </p><p>seals were contacting wet seals. While this technology was certainly the dominant method of applying mechanical seals, other designs were also commonly used. Three new seal types were introduced in the Second Edition: dry running containment seals, non-contacting seals and dual gas barrier seals. Containment seals are the outer seal in a dual unpressurized seal arrangement. In the case of a dry running containment seal, the containment seal will be exposed primarily to buffer gas or vaporized process fluid. Dry running containment seals may be either contacting or non-contacting. Non-contacting inner seals were also introduced in Second Edition. A non-contacting inner seal is designed to operate on liquid, vapor, or mixed phase fluids. Dual gas barrier seals are used in Arrangement 3 and designed to run primarily on a gas barrier fluid such as nitrogen. </p><p> The seal arrangement describes the number of </p><p>seals per cartridge, the orientations of dual seals, and the relative pressure of the buffer/barrier fluid. A chart of acceptable configurations is shown in Figure 1. Where multiple arrangements are listed in a column, they are shown in order of default selection. The arrangements are described by an arrangement code shown in the figure. </p><p> Piping plans are a critical component in the </p><p>successful design of a sealing system. These plans describe methods of controlling the environment around the seal, conditioning the sealed fluid, collecting and controlling seal leakage, and monitoring seal performance. Several new piping plans were introduced in the Second and Third Editions. These included additional options for dual pressurized liquid seals as well as new piping </p><p>plans to support containment seals and dual pressurized gas seals. The new piping plans were: </p><p> Plan 14 combination of Plan 11 and </p><p>Plan 13 is primarily used in vertical Plan 53A same as Plan 53 in the First </p><p>Edition Plan 53B closed loop with bladder </p><p>accumulator providing pressurization Plan 53C closed loop with piston </p><p>accumulator providing differential pressurization </p><p> Plan 65 monitoring atmospheric seal leakage </p><p> Plan 71 - dry running containment seals. Plan 72 - supplies buffer gas for dry </p><p>running containment Plan 74 supplies barrier gas for dual </p><p>pressurized gas seals Plan 75 collects and monitors liquid </p><p>leakage from dry running containment seals </p><p> Plan 76 collects and monitors vapor leakage from dry running containment seals </p><p> Qualification testing was one of the most </p><p>significant contributions of the First Edition. This required that seals, offered as compliant to API 682, must have successful been tested to a strict qualification procedure. The Second Edition expanded on this by defining acceptance criteria for all qualification tests. The maximum allowable leakage during testing was 1000 ppm (vol) vapors (as measured by EPA Method 21) or 5.6 g/h liquid leakage per pair of sealing faces. The maximum allowable face wear at the completion of the testing was less than 1% of the available seal face wear. Second Edition also added new tests for containment seals and dual pressurized gas seals . </p><p> Although the exact cost is unknown, it is </p><p>estimated that the seal manufacturers have invested between 5 and 10 million U.S. dollars in capital equipment in order to conduct the qualification tests specified by API 682. As the tests have been ongoing since 1994 there is perhaps an additional 5 to 10 million dollars of operating costs associated with the tests. It is likely that all manufacturers have not yet completed a full slate of tests and that API 682 qualification testing will continue for years. </p></li><li><p>Page 4 Copyright 2015 by Turbomachinery Laboratory, Texas A&amp;M Engineering Experiment Station </p><p>OVERVIEW OF THE FOURTH EDITION Although the Third Edition of API 682 and </p><p>ISO 21049 were published in 2004, the contents were essentially the same as the Second Edition of API 682 published in 2002. A Task Force was formed in 2006 to begin working on the Fourth Edition. The first assignment for the Fourth Edition Task Force was to answer questions and comments regarding previous editions. The Task Force members soon realized that major changes, including reorganization and editing, were necessary in order to clarify the specifications of API 682. NEW DEFINITIONS </p><p> API 682 has created definitions for many of </p><p>the common features and attributes of mechanical seals and systems. When new concepts are introduced or options are added to the standard, they must be captured in the definitions. The number of definitions has increased and the wording made more concise and descriptive. The longer, more involved definitions have been moved from Section 3 into the general body of the standard. For example, the definitions of Arrangements, Categories and Types have been moved into Section 4. </p><p> Mechanical seal terminology can be found in </p><p>other standards outside of API 682. Previously there had been no attempt create consistent definitions and terminology across these different standards. The definitions in the Fourth Edition have been revised to be more consistent with terms that are used in the sealing industry in general. To help accomplish this, the Task Force worked with memb...</p></li></ul>

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