The installation of reducers shall adopt corresponding processes based on material (metal/plastic), connection type (butt welding/flange/threaded/hot fusion), and service scenario (horizontal/vertical piping). The core principles are to ensure tight sealing, smooth fluid transition, and avoid stress concentration. The detailed installation procedures and precautions are as follows:
I. Pre-Installation Preparation
1. Material Acceptance
- Verify reducer specifications (size, pressure rating, concentric/eccentric) and material certificates to ensure compatibility with the pipeline.
- Inspect appearance: Metal reducers shall be free of cracks with uniform wall thickness; plastic reducers shall have no bubbles or insufficient filling.
- Check sealing surfaces (flanged reducers): Surfaces shall be flat and scratch‑free, with properly matched gaskets (rubber/spiral wound gaskets).
2. Pipeline Preparation
- Metal pipes: Cut ends shall be flat with machined welding bevels (for butt welding: bevel angle 37.5°±2.5°, root face 1–2 mm). Remove oil, grease and rust from bevel areas.
- Plastic pipes: Cut ends shall be perpendicular to the axis; deburr and smooth the ends (for hot fusion/socket connections).
3. Tool & Accessory Preparation
- Metal reducers: Welding machine (TIG/arc welding), flange bolts/nuts, gaskets, torque wrench, level/theodolite.
- Plastic reducers: Hot fusion machine (PPR/PE), PVC solvent cement, pipe clamps, tape measure.
II. Installation Procedures for Different Connection Types
1. Butt Welding Connection
(Mainstream for metal reducers, DN ≥ 50)Application: High‑pressure/high‑temperature pipelines (petrochemical, power plants), suitable for both concentric and eccentric reducers. Steps:① Alignment and PositioningMatch the large end of the reducer with the large pipe and the small end with the small pipe. Ensure coaxiality (concentric reducers) or flat‑bottom alignment (eccentric reducers on horizontal pipes).
- Eccentric reducers on horizontal pipes: Must be installed with flat side downward to prevent liquid or solids accumulation.
- Vertical pipes: Prefer concentric reducers to maintain axis alignment.
② Tack WeldingPerform 3–4 evenly spaced tack welds using TIG. Check welding gap (2–4 mm) and misalignment (≤ 10% of wall thickness). ③ Formal Welding
- Root pass: TIG welding to ensure full penetration without slag inclusions.
- Filling and capping passes: Arc welding with multi‑layer/multi‑pass technique; weld reinforcement 0–3 mm.
④ Post-Weld TreatmentRemove welding slag. Apply anti‑corrosion treatment to carbon steel welds; pickle and passivate stainless steel welds. ⑤ InspectionVisual inspection of welds (no cracks, porosity). High‑pressure pipelines require additional RT/UT testing.
2. Flange Connection
(For equipment connections/maintainable pipelines)Steps:① Flange MatchingReducer flanges shall match pipeline flanges (pressure rating, facing type). Install compatible gaskets (e.g., spiral wound gaskets for PN4.0). ② Bolt TighteningUse a torque wrench to tighten bolts evenly in a diagonal sequence in 3 stages, applying 1/3 of final torque each time to ensure uniform flange contact. ③ VerificationCheck flange gap with a feeler gauge (≤ 0.1 mm) to eliminate leakage risks.
3. Threaded Connection
(Small‑size low‑pressure pipelines, DN ≤ 50)Steps:① Thread PreparationReducer threads shall match pipe threads (G/NPT). Apply thread sealant (oil‑resistant sealant for gas pipelines). ② TighteningTighten with a pipe wrench, leaving 2–3 exposed threads. Avoid over‑tightening to prevent thread fracture. ③ Leak TestingConduct pneumatic or hydrostatic testing after installation on gas/water lines.
4. Installation of Plastic Reducers
(1) Hot Fusion Connection (PPR/PE Pipes)
Steps:① Heat the fusion machine to the specified temperature (260℃ for PPR, 220℃ for PE).② Insert the reducer socket and pipe spigot into the heating tool simultaneously and heat for 5–10 seconds (adjusted by pipe size).③ Quickly remove from the heater, insert the pipe into the reducer socket, maintain coaxiality, and cool for at least 30 seconds without rotation.④ Secure with a pipe clamp; no external force during cooling.
(2) Solvent Cement Socket Connection (PVC Pipes)
Steps:① Clean the reducer socket and pipe spigot to remove oil and dirt.② Apply PVC solvent cement evenly on both the inner socket and outer spigot.③ Insert quickly and rotate 1/4 turn, hold for 1 minute. Do not move until the cement is fully cured.
III. Key Installation Precautions
1. Orientation of Concentric/Eccentric Reducers
- Horizontal pipes:✅ Eccentric reducers: flat side downward for liquid/slurry service; flat side upward for gas lines to avoid air locking.❌ Concentric reducers are prohibited for horizontal slurry lines (prone to solids accumulation).
- Vertical pipes:✅ Concentric reducers (aligned axis for vertical flow).❌ Eccentric reducers (may cause pipe offset and stress concentration).
2. Stress Avoidance
- Leave expansion clearance when connecting reducers to valves or equipment to prevent stress from thermal expansion and contraction.
- Support large‑size reducers at 500–1000 mm from the joint to avoid weld cracking due to dead weight.
3. Pressure Testing & Acceptance
After installation, conduct system pressure testing:
- Hydrostatic test: 1.5 times design pressure, hold for 30 minutes with no leakage.
- Pneumatic tightness test (gas/vacuum lines): 1.15 times design pressure, hold for 24 hours with pressure drop ≤ 1%.
4. Special Service Requirements
- Corrosive chemical lines: Intergranular corrosion testing required for stainless steel reducer welds.
- Buried PE reducers: Backfill with sand after hot fusion to prevent mechanical damage.
- High‑temperature steam lines: Post‑weld heat treatment required for alloy steel reducers to relieve residual stress.
IV. Common Installation Errors and Corrections
- Eccentric reducer installed flat side upward on horizontal liquid lines → causes liquid accumulation and corrosion → correction: install flat side downward.
- Excessive misalignment of butt‑welded reducers → induces flow turbulence and weld cracking → correction: verify coaxiality before tack welding.
- Overheating during plastic reducer fusion → causes material carbonization and sealing failure → correction: set fusion temperature per material and calibrate heaters regularly.
