Blind (BL, BLRF, BLFF) NACE MR0175/ISO15156 Flanges

Product Description

NACE MR0175 / ISO 15156 compliant Blind Flanges (BL, BLRF, BLFF) are solid, un-bored forged piping discs specifically metallurgical-processed and tested to prevent Sulfide Stress Cracking (SSC), Stress Corrosion Cracking (SCC), and Hydrogen-Induced Cracking (HIC) in sour oil and gas upstream and refining environments containing hydrogen sulfide ($\text{H}_2\text{S}$).

1. NACE MR0175 / ISO 15156 Metallurgical & Manufacturing Requirements

Because blind flanges absorb complete bending moments and full internal line pressure across their entire center surface, NACE MR0175 enforces strict metallurgical thresholds:

Maximum Hardness Control

• Carbon and Low-Alloy Steels (ASTM A105, A350 LF2, A694): Maximum allowable hardness is 22 HRC ($\le 187\text{ HBW}$).

• Austenitic Stainless Steels (304/304L, 316/316L): Solution annealed condition with maximum hardness typically capped at 22 HRC ($\le 200\text{ HBW}$).

• Duplex Stainless Steels (2205 / F51): Solution annealed with ferrite content maintained between $35\text{--}55\%$ and maximum hardness of 28 HRC ($\le 290\text{ HBW}$).

Heat Treatment Requirements

• Carbon steel forgings must undergo full Normalization (A105N / A350 LF2), Normalizing and Tempering, or Quenching and Tempering to eliminate residual stresses from forging and machining.

Chemical Composition Restrictions

• Sulfur Limits: Typically restricted to $\text{S} \le 0.010\%$ (or $\le 0.005\%$ for critical sour service) to prevent manganese sulfide stringers that initiate Hydrogen-Induced Cracking (HIC).

• Carbon Equivalent (CE): Kept below $0.43\%$ for carbon steels to ensure weldability and prevent hard spots.

2. Structural Types & Facing Configurations

3. Applicable Standards & Specifications

• ASME B16.5: Pipe Flanges and Flanged Fittings ($\text{NPS } 1/2 \text{ to } 24$, Class 150, 300, 400, 600, 900, 1500, 2500).

• ASME B16.47 Series A & B: Large Diameter Steel Flanges ($\text{NPS } 26 \text{ to } 60$).

• NACE MR0175 / ISO 15156: Parts 1, 2 (Carbon/Low-Alloy Steels), and 3 (Corrosion-Resistant Alloys).

• NACE MR0103 / ISO 17945: Materials resistant to sulfide stress cracking in oil refining environments (downstream processing).

4. Common NACE MR0175 Material Specifications