Nearly six years of work went into the current update of the API 682 mechanical seal standard, due to come into force shortly. Since its introduction in 1994, API 682 has become "the" standard that sets the global tone for the procurement and operation of seal and supply systems for centrifugal pumps in the oil and gas sector as well as in (petro) chemistry.
The American Petroleum Institute (API) founded in 1919 has been occupying itself with technical standards since 1924. To this day, API has adopted roughly 500 standards that address the most diverse processes and components and which ensure a maximum of operating and process reliability. Individual standards - including the API 682 regulations for mechanical seals and seal supply systems - have become so popular in the meantime that they have been referenced in outside industry applications. The authors of the new edition point out that this had never been intended and clarify what API 682 is actually about: it concerns the seal systems in pumps of the oil & gas and (petro)chemical industries.
API 682 – A benchmark since the middle of the 90s Initial information about mechanical seals was originally provided in the API 610 pump standard.
During the 90s, API 682 then developed into a separate, more comprehensive standard for mechanical seals and supply systems. A typical quality of the API 682 standard is that is permanently updated by practical people. A further quality of the API 682 is that it does not normatively permit only a single technical solution. In addition to proven and tested standard solutions (defaults), the regulations also deliberately list alternatives (options) - and even allow customized solutions (engineered solutions).
The objective of API 682 is a continuous operation of the seal system for at least three years (25,000 operating hours subject to the legally stipulated emission values, or for max. "Screening Value" of 1000 ppm vol, EPA method 21), increased operational reliability, and simplified maintenance.
Coding system - with even more selectivity
The 4th Edition includes the revised product coding system. The proven classification parameters "Category," "Arrangement," and "Type" will be continued. These are now listed first. Details regarding the supply system - specified as "Plan" - are also in the old and in the new code. The addition of precise information to material selection and shaft diameter is new. This gives more meaning to the Code and guarantees a clear specification of the mechanical seal and its operation.
More precision during the selection process due to "Risk & Hazard Code"
The selection process of an API seal system is a complicated affair. Several flow charts and tables on more than 10 pages are dedicated to this topic in the new edition. In order to determine the seal arrangement more precisely, a scheme pursuant to the "Risk & Hazard Code" has been introduced in the 4th Edition for the first time. The starting point here is the pumped medium whose real hazard potential is accurately recorded and described by "Risk & Hazard Codes" in the "Material Safety Data Sheets." The selection scheme enables the quick and secure recognition of whether a single seal (Arrangement 1) is sufficient or if a double seal with barrier pressure system is required.
"Lived Standard" - practical experience counts
The "lived" standard of API 682 is also demonstrated in the new edition in that the two silicon carbide (SiC) variants "Reaction Bonded Silicon Carbide" and "Self-Sintered Silicon Carbide" can be used equally as "default" materials for sliding surfaces. Until now, sintered SiC was set for chemical applications due to its superior chemical stability, whereas the reaction bonded variant established itself in the refinery sector. This allocation was canceled due to practical application examples that were brought to the attention of the Task Force - and which called for a course correction.
Chapters 8 and 9 dealing with the hardware for the supply systems and instrumentation were subjected to intense revision. They were completely reorganized, whereby the topic is now handled in three stages - thus making it more systematic. The first block introduces the supply systems in total. The piping as well as the components are addressed next.
Seal supply systems for Plan 53 - 28 days without refilling
Plan 53 with a pressurized barrier fluid belongs to the more complicated supply systems. In detail, three types are possible: Plan 53A is the solution with the constructively least amount of effort.
The pressure on the barrier medium here is generated directly by the gas pressurization - normally with nitrogen - in the tank. However, the application has limits because higher barrier pressures could cause a dissolution of the nitrogen in the barrier medium. The consequence would be the risk of inadequate lubrication in the sealing gap of the mechanical seal. Higher barrier pressures are therefore the pursuit of Plans 53B and 53C.
Whereas Plan 53C works with a piston accumulator, putting it among the more sophisticated seal supply systems, Plan 53B uses an especially clever solution: Pressurization occurs via an elastomer bladder in the reservoir that separates the nitrogen from the barrier fluid. Pressure monitoring with consideration of the temperature in the bladder accumulator records the values and transfers them to the control room. The fill level with consideration of any temperature impacts is calculated there and the correct time for refilling the barrier fluid is determined.
A new prescribed refilling interval of at least 28 days has also been included in the 4th Edition.
Consequently, the fluid reservoir must be large enough to reliably supply the seal with barrier fluid during this entire period. To obtain as compact reservoirs as possible, the seal manufacturers are required to find optimized system solutions with minimal leakage values.
In addition, Plans 03, 55, 65A, 65B, 66A, 66B, and 99 have been newly included in the regulations.
Transmitters instead of switches
The 4th Edition heralds a change to modern transmitters for the supply systems. They may be more cost-intensive than switches, but they transmit continuous measured values in return. The control room knows the actual system status at any time and can immediately sound the alarm in case of irregularities.
The Task Force also addressed the topic of heat resistance of fittings for supply systems in an extremely pragmatic and practically oriented manner. In the past there were frequent debates about whether supply systems for high temperature applications – e.g. a 400°C-approved pump – has to be equipped with special instrumentation for the high temperature. Now the temperature specification for the instrumentation has been limited to a commonsensical 100°C. If instruments with higher temperature limits are required in the future the customer has to inform the seal vendor accordingly.
Clearer structure - easier to understand
The essential improvements - in addition to all the technical supplements and updates - are the clear structures of the latest API regulation. The body of text was tightened and restructured, while technical details and background information were placed in the Annexes.
A special detail of the 4th Edition is the new red plugs that are inserted into the supply connections of the seal gland when the unit is delivered. These plastic closures prevent the ingress of dirt in the seal. During operation, the connections are either assigned to pipelines, or the plastic plugs are replaced with enclosed metal plugs. A nice side effect: 4th Edition API seals are quickly identified by the red plugs.
The EagleBurgmann API specialists Markus Fries and Thomas B?hm (from left to right) with a new developed API mechanical seal and the corresponding seal supply system according to API Plan 53B.
EagleBurgmann & API
EagleBurgmann is one of the leading international providers of industrial seal technology that is used in diverse industries (oil & gas, power, refinery, chemical, energy, food, paper, water, and mining, among others). The company employs roughly 6,000 employees worldwide. 60 subsidiaries and 250 locations stand for global presence - and the associated proximity to the customer. The comprehensive product portfolio includes everything from well-engineered serial seals to application-related individual constructions.
API conform mechanical seals and supply systems take an important place in the EagleBurgmann range. For more than 20 years, the company has been consequently providing its know-how in further developing API specifications for the design of seal systems for the oil & gas and (petro) chemistry sectors - and is active in the API 682 Task Force. Worldwide there are more than 21,000 EagleBurgmann API seal systems in use.
The principle innovations of API 682 4th Edition at a glance:
- Adaptation of pressue limits: 20 bar(g) Category 1, 40 bar(g) Category 2/3
- Detailed notes to "Engineered Seals"
- Combination of "Seal Types" in Arrangement 2/3
- Definition of vapor pressure margin
- Overview table of internal gap dimensions
- Selection SiC face material independent of category
- Optional bellows material Alloy 718 for metal bellows seals Type B
- Additional requirement for set screws for torque transmission
- New details to selection and operation of pressurized double seal systems
- Reduced minimum gap at the internal pumping device
Seal supply systems
- Transmitters instead of switches
- Alternative arrangement selection method on the basis of Risk & Hazard codes
- New API Plans 03, 55, 65A, 65B, 66A, 66B, 99
- Hydrostatic level detection for Plans 52, 53A
- Temperature measurement of gas bubble for Plan 53B
- 28-day refilling interval for barrier pressure systems
- Minimum pipe wall thicknesses of 2.5 mm for welded joints
- Temperature limits for instrumentation