API 608 Vs API 6D: Valve Standard

API, or the American Petroleum Institute, is a global stalwart of leading standards applicable to the oil and natural gas industry. The institute is accredited by the American National Standards Institute (ANSI) and has issued nearly 700 census standards that govern various aspects of the oil and gas industry, including valves. 

API valve standards comprise guidelines and recommended practices concerning safety, equipment, management, materials, spill prevention, and environmental protection for different valve types. These frameworks set standards for all industrial valves manufacturers and are a mark of sound engineering practice, adherence to market demands, and a promise of high-quality materials and manufacturing processes. The guide below will lay out the fundamentals of 

Differences Between API 608 Vs. API 6D

API 608 refers to specifications for flanged, threaded, and welded ball valves made from metal, whereas API 6D refers to specifications for piping and pipeline valves. Both of these valve standards are related to ball valves and provide detailed requirements in terms of test methods, structural design, and performance requirements, among other things. 

Together these standards comprise specifications for ball valves that are exclusively used in the petrochemical industry and refineries. While API 608 includes subclauses such as design, operation, and performance based on the ASME B16.34 standards, the latter is applicable to engineering principles for long-distance pipelines. Listed below are some basic points of comparison between the two.

Structure And Application 

The API 608 standard is applicable to ball valves used in the oil and gas industry in pipelines used to allow or shut off the flow of media. These valves are typically used in environments of high pressure and temperature and are subject to inflammable and explosive mediums. Since these valves are used in pipelines that are under constant operation, they require strict standards when it comes to materials, valve sealing, and anti-corrosion properties. Ball valves that utilize this standard have a fixed floating ball structure. 

On the other hand, ball valves that adhere to the API 6D standard are specifically used in pipelines that transport mediums over long distances. API 6D ball valves can also have other structural designs and can be made from materials other than metal to optimize their sealing performance. 

The diameter of their cavity can also be designed to be bigger to prevent blockage or damage to the seat or ball via foreign matter like sand, stones, or rocks. As for the structure, ball valves under the API 6D standard have a fixed ball structure. 

Additional Applications Of API 6D Valves

Apart from allowing or stopping the flow of the medium, these ball valves have additional functions. These include leak detection, overpressure relief, grease injection, and emptying, among others. To reduce the impact on the environment, improve safety during urgent repair, and cut costs, the discharge and venting of pipeline ball valves are crucial. 

This is why the discharge and venting structure needs to conform to the API 6D specifications and meet the guidelines for vent and discharge ports. For ball valve seats that have the additional function of draining and venting, the valve seat should be able to withstand full pressure differences outside. It should also be able to isolate both downstream and upstream fluids to achieve safe discharging and venting. 

In the factory test for API 6D valves with this function, the sealing performance of the valve seat is thoroughly tested. Any dirt in the valve cavity is drained for the pipeline, and the valve is put into operation, and when the repair process is underway, these valves are used to discharge and vent media in the pipeline. 

Installation And Maintenance

Ball valves that fall into the API 608 category are easy to install and are typically pre-installed in the factory before they are stored and transported. Since API 6D ball valves are specifically used in long-distance oil and gas pipelines, they have a large diameter, which makes installation slightly tougher compared to API 608 ball valves. 

API 608 ball valves that adhere to valve standards are durable, offer long-term safety, and are highly reliable. They are easy to maintain or replace because of their durability and ease of installation, respectively. Since API 6D ball valves are installed in harsh environments, regular maintenance is essential to avoid any hazards. 

These ball valves are difficult to replace due to their caliber, welding connections with pipelines, and buried installation. Hence, they need to have greater safety, reliability, tightness, and strength relative to API 608 valves. 

Application And Specifications

API 608 ball valves are utilized in the oil and gas industry for industrial-scale applications. They are usually used with the ASME B31.3 process pipelines that have a diameter range of NPS (¼- 24). They have a pressure class of 150, 300, 600, and 800 pounds and have a floating ball structure that is sealed at the pipe outlet.

API 6D ball valves are also used in the oil and gas industry in long-distance pipelines, including ASME B31.8 and B31.4. They have a diameter range of NPS (4-60) and have a pressure class of 150, 300, 400, 600, 900, 1500, and 2500. They have a fixed ball structure that is sealed at the pipe inlet. 

Testing And Inspection

In API valve standards, there are detailed requirements for the inspection and pressure testing of the ball valves, which fall under its category. Since API 608 valves are a supplement of ASME B16.34, these valves are also required to meet the inspection and test guidelines of ASME B16.34. 

The latter and API 598 provide basic specifications for general-purpose valves. The seal of API 608 valves is generally tested by pressurizing one end and observing the valve’s seat at the other end in the seal test. API 6D has more detailed requirements for the testing and inspection of valves used in long-distance pipelines. 

Since these valves are subject to high temperature and pressure, the inspection and testing guidelines under this standard are more demanding as compared to API 608 valves.  For example, for inspection purposes, an industrial valve company will subject these valves are subject to longer pressure durations, have more test items, and have more complex operating procedures. In these valves, the seal is tested from the middle chamber by pressurizing one end. 

QSL In API 6D Valve Standards

In the latest version of API 6D valve standards which was released in 2014, an additional requirement is that of QSL (Quality Specification Level). QSL specifies detailed requirements for NDE or non-destructive testing, manufacturing process documentation, and pressure testing.  The QSL required for API 6D ball valves varies according to the ball valve type and has different test items. QSL-1 is the minimum quality specification level required by API 6D ball valves. In general, the higher the QSL grade, the more stringent the requirements. Additionally, the buyer must specify that the ball valve should conform to QSL-(2-4).

Final Words

The petroleum industry requires highly safe and durable valves that do not cut corners when it comes to quality. API valve standards are a mark of engineering perfection, reliability, and safety and must be followed by all valve manufacturers.  

Dombor is a leading China valve manufacturer of quality valves that adhere to API 608 and 6D standards. Contact the professional valve supplier today to revel in the unparalleled quality of its products.