API 6A "ENGINEERING TRIM STANDARD"

ENGINEERING STANDARD

 1. SCOPE

This Engineering Standard provides guidelines for selection of materials based on API 20th Edition.

2. REQUIREMENTS

2.1. Material Class ZZ shall not be a standard material class designation unless customer requires it.

2.2. Partial pressure is included after the standard material class designation for material classes DD to HH. For example, FF-0.5 indicates that that product can only be used where the partial pressure is equal to or below 0.5 parts per million (PPM). Material class AA, BB and CC does not come under NACE jurisdiction as they are for General Service.

2.3. For body, bonnet, end and outlet connections, DD-NL is equivalent to EE-NL.

2.4. Hangers which are FF-NL must be manufactured from Inconel 718. Clarifications should be raised to customers whether FF-1.5 is sufficient.

2.5. NACE does not apply to components that are loaded in compression.

2.6. Refer to Table 1 for the material selection guide.

3. CALCULATION OF H2S PARTIAL PRESSURE

3.1. The H2S partial pressure can be calculated from the information given by customer with regards to the H2S concentration. Assume that well shut in pressure = 5,000psi in both cases:

3.1.1. H2S in mole %. Assuming H2S = 2%

 Partial pressure = 5,000 x 2 x 0.01 = 100 psi

3.1.2. H2S in parts per million (PPM). Assuming H2S = 10 ppm

 Partial pressure = 5,000 x 10 / 1,000,000 = 0.05 psi

Material Component Highest M/C H2S max (psi) pH min Max Temp. °F

Low alloy steel

(4130, 4140, 4340, F22 with YS ≤ 80ksi)

Table 1: API Material Class designation guide for NACE service