Selecting the Right Material for Medium and Low Pressure Pipe Flanges: A Procurement Guide

Cast Iron

Cast iron flanges (e.g., ASTM A126 Class B) are often used in low-pressure, low-temperature applications such as water distribution, drainage, and HVAC systems. They are economical but brittle and not recommended for shock loads or cyclic stress.

Pros: Low cost, good machinability, adequate for non-critical water systems.
Cons: Low tensile strength, poor impact resistance, limited to 1.5 MPa (approx. 225 psi) and 300°C max.

Stainless Steel

Stainless steel flanges (e.g., ASTM A182 F304/L, F316/L) are chosen when corrosion resistance, hygiene, or high-temperature performance is required. Common in chemical, pharmaceutical, and food processing industries. Austenitic grades offer excellent toughness down to cryogenic temperatures and resistance to many acids.

Pros: Superior corrosion resistance, long service life, high-temperature capability (up to 800°C for some grades).
Cons: Higher cost, potential for chloride stress corrosion cracking (avoid marine environments with 304L).

Standards to Confirm

When specifying flanges, verify compliance with these international standards:

Ensure the material grade matches the standard's pressure-temperature ratings.

Inspection and Documentation Requirements

For procurement of medium/low pressure flanges, request the following documents:

• Material Test Certificate (MTC) per EN 10204 3.1 or 3.2 (or equivalent)
• Chemical composition and mechanical properties report
• Heat treatment records (if applicable)
• Dimensional inspection report (per ASME B16.5 tolerances)
• Non-destructive testing (NDT) certificates: visual, dimensional, optionally dye penetrant or magnetic particle
• Surface treatment details (e.g., oiled, galvanized, passivated)

RFQ Checklist: What to Specify

When requesting a quotation, provide these details:

1. Flange type (weld neck, slip-on, blind, threaded, etc.)
2. Nominal size (NPS or DN) and pressure class (150, 300, 600, or PN6, PN10, PN16, etc.)
3. Material grade (e.g., ASTM A105, A182 F304, EN 1.4401)
4. Facing (raised face, flat face, ring joint)
5. Quantity and delivery schedule
6. Certification requirements (MTC, NDT reports)
7. Special tests (PMI, hardness, hydrostatic)

Quality Risks to Watch

• Substandard material substitution – always request MTC and perform random PMI (Positive Material Identification) on arrival.
• Dimensional errors – confirm bolt hole alignment, flange thickness, and hub length per standard.
• Surface defects – cracks, pits, or scale can lead to leakage under pressure.
• Incorrect heat treatment – for carbon steel, normalizing or annealing ensures proper mechanical properties.

What to Send Before Quotation

To get accurate pricing and lead time from Hebei Haihao Group, please provide:

• A clear flange specification (or a drawing)
• Quantity and preferred delivery incoterm
• Required certifications and third-party inspection (if any)
• Any project-specific requirements (e.g., NACE MR0175 for sour service)

Why Partner with Hebei Haihao Group

We are a direct manufacturer of forged flanges, pipe fittings, and piping packages for over 30 years. Our products comply with ASME, EN, JIS, and ISO standards. We offer:

• Competitive pricing without compromising quality
• Full traceability with EN 10204 3.1 certificates
• Short lead times for popular sizes and materials
• Custom machining and special coatings available

Contact us today for a quotation tailored to your medium/low pressure flange needs.