304 Welding Flange

Three major values of 304 welding flange

1. Basic corrosion resistance

Passivation film protection: Cr≥18% forms a dense oxide film, which can withstand:

Fresh water, steam, weak organic acid (pH>4.5)

Urban atmospheric corrosion (humidity≤80%)

Warning: If the chloride ion concentration in seawater/bleach is >50ppm, pitting corrosion will occur, and 316 needs to be upgraded.

2. Cost-effectiveness proof

Material Initial cost 10-year maintenance cost Comprehensive cost index

Carbon steel flange 1.0x 4.2x 5.2x

304 welding flange 1.6x 0.5x 2.1x

316 flange 2.3x 0.3x 2.6x

3. Structural adaptability

Type Maximum pressure level Advantage scenario Stress concentration factor

Loose flange Class 900 Frequent disassembly/corrosive media -

Butt weld neck Class 2500 High pressure/vibration pipeline ↓40%

Socket weld Class 600 Small diameter (DN≤80) clean fluid ↓25%

Failure scenario and solution

Failure scenario Cause analysis Solution Cost impact

Sour natural gas Hydrogen sulfide stress corrosion cracking Nickel-plated carbon steel flange -20% unit price

Yogurt fermentation tank Lactic acid corrosion (pH=3.8) Choose 316L flange +40% unit price

Cooling pipe of coastal power plant Chloride ion corrosion (>200ppm) Upgrade 316 flange +35% unit price

FAQ

Q1: How to visually distinguish 304 Welding Flanges from inferior 201 stainless steel flanges?

A: Three steps: Magnetic test: 304 weak magnetism (slight magnetic attraction in cold working area), 201 strong magnetism

Chemical solution detection: drop 304 reagent → turn red (nickel content ≥8%), 201 does not change color

Gloss comparison: 304 is silvery bright, 201 is dark gray

Q2: Can 304 flanges be welded? Will it reduce corrosion resistance?

A: It can be welded! But it is necessary to: use 308L welding materials, pickle and passivate the weld area after welding

It is strictly forbidden to pollute carbon steel tools

Q3: Does the "short section" of the loose flange have to be made of 304?

A: It must be! The short section is in direct contact with the medium. If carbon steel is used: the electrochemical corrosion rate is accelerated by 5 times

The service life is reduced from 10 years to ≤2 years

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