Why API Guidelines Should Guide your Selection of Gate Valve Lubricant

The American Petroleum Institute (API) standards give comprehensive guidelines for gate valve materials and performance on valves and wellhead equipment – but they are also an essential tool when selecting gate valve lubricants.

By Brian Presson, Business Development Manager

In many ways, the API 6A gate valve is the unheralded hero of safety in the oil & gas industry. At its core, the API 6A gate valve is a very simple piece of machinery, purpose built to perform a very specific job. It consists of a body, bonnet, packing, stem, seats and gate – and it’s used to either open and shut off the flow of pressure on oil wells, on both Christmas trees and wellheads.

The API 6A gate valve may be simple, but it’s also essential for safety – which is why the API has developed very specific guidelines for gate valve selection. These guidelines cover a wide range of criteria, from Product Specification Levels and Product Requirements to Material Classes and Temperature Ratings.

The API 6A guidelines don’t explicitly define lubricant requirements for gate valves, but they do provide a comprehensive framework for better lubricant selection. By recognising the symbiotic relationship between the gate valve specifications and lubricant compatibility, you can enhance the overall reliability, safety and longevity of your oil & gas operations.

Understanding the basics: The role of lubrication in a API 6A gate valve

When an API 6A gate valve closes, the gate generates a full metal-to-metal seal between the gate and downstream seat, which is energised by bore pressure acting on the upstream side.

The basic functions of the lubricant are to reduce wear and friction of internal valve components, provide corrosion protection and reduce contamination from flow line products in the valve cavity. This protects the internal components during service, helping ensure the metal-to-metal seal remains true whenever the valve is closed.

When it comes to gate valve lubricants, a harmony of factors create a ‘Wall of Strength’ to ensure seamless operation and longevity of the valve.

• Chemical : To have total resilience against the range of aggressive hydrocarbons encountered in the well chemistry
• Thermal: The ability to maintain consistency across a wide temperature range as seen at the wellhead.
• Physical: Characteristics which ensure the lubricant isn’t blown out or displaced by high pressure and velocity preventing washout
• Mechanical: Withstands the applied loads on components from the acting wellbore pressure whilst assisting with metal-to-metal sealing.

RS Clare gate valve lubricants meet the above requirements. They have also been developed with the API 6A guidelines in mind. This means you can use the API 6A as a guide during lubricant selection to ensure you get the ideal lubricant for your specific operating environment.

Trim Level Material Classes, as defined by API 6A
‘Valve trim’ refers to the parts of a valve that are normally exposed to process fluid. These components include the body, bonnet, gate, seat, stem and bonnet seal ring gasket.

To ensure safety, API 6A specifies standard Material Classes for trim compenents, using a unique number set to describe each material. These Material Classes ensure that trim components effectively seal and contain pressure by minimising adverse effects between the medium in the valve and the metallurgy of the valve itself.

The API 6A Trim Levels run from AA through to HH. AA, example, specifies 4130 steel alloy for all trim materials, apart from the bonnet seal ring gasket, which is 1018 steel alloy. To determine the Material Class, you need to ascertain the corrosivity of the retained, produced or injected fluid, considering various environmental factors and production variables. Consideration should also be given to the carbon dioxide partial pressure, which generally relates to corrosivity in wells.

The relevance of this API guideline to lubricant selection is obvious. The lubricant will be in direct contact with both the trim and medium inside the valve, and should effectively work to prevent any adverse effects between the two. Factoring in the Trim Levels and Material Class when selecting your lubricant can, therefore, greatly improve the valves’ function and will provide better protection for its components, ensuring the proper functionality of the valve over a longer period of time.

Temperature Ratings as defined by API 6A

API 6A designates 8 different Temperature Ratings, which outline the allowed operating temperature range of the gate valve, from the minimum ambient air temperature to the maximum temperature of the well fluid passing through or contained by the equipment.

Often, these Temperature Ratings can be used in combination with one another to achieve a wider rating. For instance, a common Temperature Rating rating for an API 6A gate valve is PU, which combines the lower limit of the P temperature range and the upper limit of the U temperature range.

API 6A Temperature Ratings are integral to lubricant selection, as they enable you to select a lubricant that will continue to perform effectively under the specific operating temperatures of your application.

Choosing a lubricant with a broad effective operating temperature that is well-matched to the API 6A standard Tamperature Range for the relevant gate valve will ensure consistent valve functionality, minimising the risk of malfunctions in extreme conditions. This is as important as the lubricant’s 4-ball weld load performance. The 4-ball weld load is a good barometer of the lubricants’ ability to effectively coat and protect a sealing surface. But, if the temperature range is not aligned with the designated operating environment of the valve, the lubricant will deteriorate long before the 4-ball weld load becomes a factor.

API 6A Product Specification Levels and Product Requirements

API 6A defines Product Specification Levels (PSLs) to categorise equipment for oil & gas applications based on their design, manufacturing and testing requirements. These levels run from PSL1 to PSL4 and are crucial in ensuring equipment reliability and safety.

In addition, API 6A Product Requirements (PR1 and PR2) outline additional criteria for oil & gas equipment. API 6AV1 is also a critical standard in the oil & gas industry, primarily focusing on valves subjected to the abrasive challenges of handling sand slurry (i.e. gate valves that operate in environments where sand and solid particles are present).

The physical characteristics of the lubricant plays a pivotal role in meeting the exacting PSL, PR and AV standards, particularly those set out in API 6A PR2 and API 6A AV1.

• During API 6A PR2 testing, low to high thermal and pressure loading is exerted over extended cycles. In this context, the lubricant’s structural integrity is essential to providing sustained protection to the valve’s interacting components. Lubricant properties such as stiffness (cone penetration test), apparent viscosity (rheological test), adhesiveness (water spray off test) and EP and AW (4-ball weld test) all play a part in carrying the valve through this endurance testing.
• In API 6A AV1 testing, these same lubricant properties are equally indispensable. But, because the test simulates full flow conditions of a sand slurry, it is paramount that the lubricant can also remain firmly in the cavity under high flow and valve cycling in order to block sand ingress. Furthermore, if the sand damages the seal faces during the test (500 cycles), a lubricant with additional sealing capability is hugely beneficial.

Delve deeper into the API 6A requirements and lubricant selection

The selection of appropriate equipment for oil & gas operations is a multifaceted process that hinges on the interplay of PSLs, PRs, Material Classes and Temperature Ranges. A simplistic approach to lubricant selection – the all-too common generic ‘body fill grease’ approach – undermines the meticulous product selection process articulated by API 6A and its requirements.

That’s why we at RS Clare take API 6A guidelines and requirements into consideration when developing and specificing lubricants for gate valves. If you’d like to know more about this work, get in touch with us.