5 Things to Know Before Buying api 6a wellhead valves

Learn about how valve trim levels influence the valve trim material selection.

When purchasing a valve there are many different things to consider. One of the most important considerations is the level of trim required for your valves. The valve trim material selection changes when moving from one level to another for some of the pressure containing parts.

What Are the Different Valve Trim Levels?

Valve trim levels range from AA through HH, and there are specific differences for each of these. Trim levels will determine the most suitable application for your needs and the required materials for the internal components of the valve.

The components affected by trim level changes include the:

• Body
• Bonnet
• Gate
• Seat
• Stem
• Bonnet seal ring gasket

Valve Trim Level AA

AA is your general non-corrosive trim level. The material used in the AA trim level is 4130 for all components with the bonnet seal ring gasket being 1018.

Valve Trim Level BB

BB is used in a general and slightly corrosive environment. The body and bonnet will be made from 4130, the gate and seat will be 410 Stainless Steel, it will have a 17-4 Stainless Steel Stem, and a 316 Stainless Steel bonnet seal ring gasket.

Valve Trim Level CC

The CC valve trim type is used in a general, moderately corrosive environment with CO2. The body, bonnet, gate, and seats will all be 410 Stainless Steel. The stem will be made from 17-4 Stainless Steel, while the bonnet seal ring gasket will be 316 Stainless Steel.

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Valve Trim Level DD

DD-NL and DD-0.5 valve trim types are for sour, non-corrosive environments. All components in both trim levels are 4130 with the only difference being that DD-0.5 has a 17-4 Stainless Steel stem whereas the NL will most likely have a 4130 stem.

Valve Trim Level EE

EE trim levels, like DD trim levels, are used in sour environments. EE-0.5 is used when the environment is slightly corrosive. EE-1.5 is used in highly corrosive environments with moderately abrasive CO2 present, and EE-NL is suitable when highly abrasive CO2 is present.

In all EE Trim levels, the body and bonnet are made from 4130 material. All gates, seats and bonnet seal ring gaskets are Stainless Steel, with the gate and seats being 410 Stainless Steel and the bonnet seal ring gasket being 316 Stainless Steel. The difference in EE trim levels is the material used for the stems:

• EE-0.5 uses a stem made from 17-4 Stainless Steel.
• EE-1.5 uses a stem made from 410 Stainless Steel.
• EE-NL uses either an Inconel 718 or Nitronic 50 stem.

Valve Trim Level FF

FF Trim levels are also used in a sour environment. FF-0.5 is for moderately corrosive environments with H2S. FF-1.5 and FF-NL are for highly corrosive environments with CO2 and H2S. The body, bonnet, gate, and seats are all made from 410 Stainless Steel, and the bonnet gasket is made of 316 Stainless Steel. The only part that is different between the three FF trim levels is the stem:

• For FF-0.5 the stem is made from 17-4 Stainless Steel.
• FF-1.5 uses a 410 Stainless Steel stem.
• FF-NL uses either an Inconel 718 or Nitronic 50 stem.

Valve Trim Level HH

The last trim level is HH-NL, which is used in a highly corrosive and extreme service environment. The body and bonnet are both made from 4130 and have a 625 inlay throughout. The gate, seat, and stem are all made from 718 Inconel, and the bonnet seal ring gasket is a 316 Stainless Steel.

What do the designations 0.5, 1.5 and NL mean after the trim class?

It is very common to see the designations EE-0.5, EE-1.5 or EE-NL on API 6A products. This helps identify the maximum allowable partial pressure of Hydrogen Sulfide when used within the environmental limits specified in NACE MR0175/ISO 15156. More recently API 6A has determined that marking -NL is no longer necessary and should just be marked as the material class. For example, on a Tee or Cross made with 4130 75K material with no maximum allowable partial pressure, the marking should just state EE. Marking of partial pressure is now only required when there is a limit.

When purchasing a new valve, it is important to understand the environment in which the valve is used, and which trim levels will be best suited for your situation. Let Heshka Oil make that task easier by providing expert knowledge when it comes to the right valve for your project.

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