An Essential Guide To API 6D vs API 598 Comparison | Dombor

Home An Essential Guide To API 6D vs API 598 Comparison | Dombor

Several API, ASME, and MSS papers cover every element of the design, functionality, examination, and testing of the values. Only a skilled valve engineering professional can specify and acquire valve goods due to the array of regulations, standards, and specifications.

Valves utilized in petrochemical and refinery projects must adhere to a variety of regulations and guidelines set forth by several supporting associations. Modern valve standards are dynamic papers that take into account good engineering practice, shifting consumer preferences, technological advancements, and modifications in production methods. 

The American Petroleum Institute (API), which depicts roughly 650 firms, is the biggest trade association for the natural gas and oil industry. There are different types of API valve standards, including API 526, API 527, ANSI/API 574, ANSI/API 576, ANSI/API STD 594, API 598, ANSI/API 599, ANSI/API 600, API 602, ANSI/API 603, ANSI/API 607, ANSI/API 608, API 609, API 6D, API 6FA, API 6FC, API 6RS, API 11V6, ANSI/API RP 11V7, API 520-1, and API 520-2. However, API 598 and API 6D are mostly used standards and are discussed below. 

What Is API 598 Valve? 

API 598 valve
Source: Unsplash

Industry requirements for valve ratings and valve leaks are delivered by API Standard 598 from the American Petroleum Institute. As of now, the standard is in its ninth edition, which was published in 2009. For the nonmetallic-seated, resilient-seated, and metal-seated valves, API 598 specifies the analysis, assessment, and testing procedures. It covers various types of valves, including glove, plug, gate, check, butterfly, and high pressure ball valve models.

API 598 covers the inspection and testing of valves. It applies to inspection and testing carried out by the valve maker, further inspections carried out at the manufacturer’s site, and pressure tests conducted at the facility. API 608 specifies the inspection, examination, and pressure testing of ball valves in line with API 598’s examination and testing of valves. API 598 and ASME B16.3 are fundamental specs for common purpose valve models. 

The gate, plug, globe, floating ball, check, trunnion mounted ball valves, and butterfly valves must undergo shell testing. All gate and globe valves have to undergo backseat tests. Based on the size and class of the valve, closure tests are necessary for all plug, check, gate, globe, butterfly, floating ball, and trunnion mounted ball valves (both high pressure and low pressure). 

What Is API 6D Valve? 

API 6D ball valve
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For the transfer of long-distance pipelines, API 6D ball valves are employed. According to this specification, the ball valve can perform additional tasks like blowdown, clearing, overpressure assistance, lubricant injection, and on-line leak observation apart from turning on or off the medium. The architecture of API 6D ball valves is almost entirely fixed. The blowdown or empty-out of the pipeline ball valve is more crucial in terms of economy and environmental conservation.

In order to make sure the sealing performance of the valve, API 6D ball valves can use different structure designs or materials. For example, they can use body structures with massive storage areas or boost the diameter of the body cavity. This prevents gravel, stones, and different foreign objects from staying in the cavity for an extended period of time and harming the seat and the ball.

The QSL criteria have been updated to the most recent API 6D 2014 version. Nondestructive testing (NDE), pressure testing, and manufacturing method documentation all have specific QSL requirements. The API 6D ball valve inspection and test items vary for each QSL need. The API 6D minimum quality specification level is QSL-1. If the QSL grade is high, the provisions and criteria will also be high. The purchaser can determine that the ball valve needs to harmonize to QSL (2 to 4) quality specification grade. 

Differences Between API 598 Vs API 6D 

Check out the common differences between these standards when it comes to API 6d Vs API 598 comparison. 

Main Purpose 

The primary purpose of the API 6D and API 598 are totally different, which is briefly listed below. 

  • API 598 (Valve Inspection And Testing) 

The testing and examination specifications for plug, butterfly, gate, globe, check, and ball valves are covered by API 598. The API 598 test pressures for steel valves must be specified using the steel valve pressure ratings contained in ASME or ANSI B16.34.

  • API 6D (Specification for Pipeline Valves) 

The major standard for pipeline service valves, such as ball, gate, plug, and check valves, is API 6D. Even if the valve may have been manufactured by API 600, 602, 608, or 609 design specifications, refinery and petrochemical buyers occasionally refer to the more rigorous testing regulations of API 6D.

Industry Applications 

Common testing regulations for valves built in accordance with API 602, API 608, API 609, and so on are covered by API 598. Pipeline valves made for oil and natural gas are explicitly specified by API 6D. 

In comparison to ASME B16.34 and API 598, API 6D establishes more stringent standards for the examination and testing of pipeline valves, including longer pressure times, a greater number of test items, and more complicated operating methods.

Tests They Specify 

The API 598 and API 6D specifies different tests and examinations, which are listed here. 

  • API 6D

The API 6D specifies the following tests, including hydrostatic shell test, hydrostatic seat test, and stem backseat test. 

1. Stem backseat test 

  • Based on the valve size, pressure at 1.1 times valve rating for about two to five minutes  
  • No apparent leaks 

2. Hydrostatic shell test 

  • Based on the size of the valve, pressure at 1.5 times valve rating for about two to 30 minutes
  • No apparent leaks 

3. Hydrostatic seat test 

  • Based on the valve size, pressure at 1.1 times valve rating for about two to five minutes
  • No discernible leakage with soft-seated valves.
  • Valves with metal seats: Leakage cannot occur more than twice.
  • API 598 

When it comes to API 598, it specifies multiple tests and examinations, including visual examinations, backseat tests, shell tests, and closure tests. 

1. Visual assessment 

  • Ensure that all valve bodies, bonnets, covers, and closing components adhere to all adequate requirements.

2. Backseat examinations 

  • Low-pressure and high-pressure backseat test
  • Check for leaks at the seal through the stem or shaft.

3. Shell examinations

  • Shell testing 
  • High-pressure pneumatic shell testing 
  • Verify the integrity of the valve’s pressure-containing structures.

4. Closure examinations

  • Low-pressure and high-pressure closure tests 
  • High-pressure closure examinations with double blocks and bleeds
  • Check for leaks in the closure mechanism.

Test Duration 

The test durations for the API 6D and API 598 tests and examinations also vary greatly. 

  • API 6D 

When the size of the valve is ½ to 4 NPS, the back seat test, shell test, and also seat test need about 120 seconds. If the valve size is equal to or greater than 6 NPS, then the back seat test takes about 300 seconds, and the seat test needs around 300 seconds. 

If the valve size ranges between 6 to 10 NPS, the shell test takes about 300 seconds. The shell test requires 900 seconds to perform the test on valves that vary from 12 to 18 NPS in size. In addition, a total of 1800 seconds is required for a shell test if the valve size is equal to or greater than 20 NPS. 

  • API 598 

If the valve size is less than or equal to 2 NPS, the shell test takes 15 seconds, the back seat test takes 15 seconds, and the closure check test takes a total of 60 seconds. In case if the valve size is between 21/2 to 6 NPS, then the shell test, back seat test, and even closure check test take 60 seconds each. 

If the size of the valve ranges from 8 to 16 NPS, the shell test takes 120 seconds, the back seat needs 60 seconds, and the closure check test takes 120 seconds. However, when the valve size is equal to or greater than 14 NPS, 300 seconds are needed for the shell test, 60 seconds for the back seat test, and 120 seconds for the closure check test. 

Difference In Test Medium 

When it comes to the test medium used in various tests of API 6D and API 598, the test medium or the liquids vary. 

For hydrostatic shell tests and backseat tests, the test medium for API 6D is freshwater (it might comprise a corrosion inhibitor). However, the test medium for API 598 is air, water, inert gas, kerosene, or non-corrosive fluid. 

For low-pressure closure tests, the test medium for API 598 is air or inter gas, whereas the test medium for API 6D is air or nitrogen. 

For high-pressure closure tests, the test medium for API 598 is air, kerosene, inert gas, water, or non-corrosive liquid. When it comes to API 6D, the test medium is freshwater (for hydrostatic) and inert gas (for pneumatic). 


Two of the most commonly used standards in the valve industry are API 598 and API6D, specific to oil and gas projects. Knowing what types of tests they specify and for which valves are vital when taking part in an oil and gas project. 

For acquiring the best quality models of different valves, including ball valves, globe valves, gate valves, butterfly valves, check valves, or plug valves, make sure to contact a trusted valve manufacturer and get quotes for the bulk orders.

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