Answers

• 
  Is there a risk of the zinc coating peeling off after bending or threading?

  Hot-dip galvanized layers are zinc-iron metallurgical bonding layers. Bending or threading after galvanizing poses a risk of zinc layer cracking and localized peeling. The larger the bending radius, the lower the risk; thread cutting causes more significant damage to the zinc layer.

  It is recommended to complete bending and threading before galvanizing; if galvanizing is necessary, damaged areas must be repaired with zinc-rich materials in accordance with ASTM A780. Minor cracks are within the standard allowable range, but large-area spalling and exposed iron are unacceptable.

  
  
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  What are the common types of aluminum corrosion?

  1. Pitting Corrosion: Pitting corrosion is a localized dissolution that occurs at the point where the passivation film breaks. It is one of the most important corrosion modes for aluminum because it can penetrate deep, localize, and is difficult to detect early. Chloride contamination is a typical triggering factor.

  2. Electrochemical Corrosion: Aluminum may preferentially corrode when electrically coupled to a more valuable metal in humid conditions. This is both a design and a chemical issue: dissimilar metal contact, trapped moisture, and poor isolation all increase the risk.

  3. Crevice Corrosion: Crevice corrosion occurs in shielded, enclosed areas where the local chemical composition differs from the open surface. It is closely related to pitting corrosion because both are caused by passivation film breakdown and localized electrochemical imbalances.

  4. Filament Corrosion: Filament corrosion manifests as random, unbranched white tunnels of corrosion products, usually under coatings or on unprotected metal. It typically causes more damage to appearance than strength, although thin sheets can be perforated.

  5. Intergranular Corrosion: Some aluminum alloys are susceptible to intergranular attack when alloying or heat treatment produces unfavorable grain boundary precipitation. A typical example is high-magnesium forged alloys, where almost continuous Al₈Mg₅ precipitation at grain boundaries increases susceptibility to spalling or stress corrosion cracking.

  In addition to the above types, aluminum alloy corrosion also manifests as the following phenomena:

  Uniform corrosion: Overall surface thinning, commonly seen in acidic environments (e.g., annual corrosion rate exceeding 50 μm at pH < 4).

  Crevice corrosion: Caused by oxygen concentration differences at fastener joints, such as in the riveted parts of aircraft skin.

  Filamentous corrosion: Spreads in a spider web pattern under organic coatings, and is prone to occur when humidity is >65%.

  
  
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  What is the difference between a perforated pipe and a filter cylinder?

  A perforated tube is only the perforated metal skeleton, normally with open ends, without mesh or a seal.

  A filter cylinder is a finished filter element, usually with a perforated tube as the inner support, outer woven mesh / sintered mesh, end caps, and a sealing gasket for direct installation.

  
  

  While there is some overlap between perforated pipes and filter cylinders, they have different primary focuses.

  Perforated pipes emphasize their tubular structure, fluid flow, support, protection, and perforation design. Filter cylinders, by contrast, focus on filtration precision, end caps, connection interfaces, sealing, and their specific function within a filtration system. A perforated pipe can serve as the core body of a filter cylinder, or it can function independently as a ventilation pipe, support pipe, protective sleeve, or silencer pipe.

  
  

  Comparison Dimension	Perforated Pipe	Filter Cartridge
  Main Functions	Flow passage, filtration, support, protection, noise reduction	Filtration, interception, serving as filtration element for equipment
  Structural Focus	Pipe diameter, hole pattern, hole pitch, open area ratio, roll-forming & welding	Filtration accuracy, end cap, connection port, sealing, welding
  Common Types	Round pipe, long pipe, partially perforated pipe, support pipe	Flanged cartridge, conical cartridge, end-capped filter cartridge, microporous filter cartridge
  Selection Focus	Balance between structural strength and flow area	Compatibility of filtration accuracy with equipment sealing performance
  Customization Methods	Customized by plate thickness, hole diameter, pipe diameter and length	Customized by equipment specification, medium property, connection port and filtration requirements