Air-Cooled Heat Exchangers (Fin-Fan) NDT Guide
Authoritative API 661 engineering guide for forced draft and induced draft air-cooled exchangers. Learn how Near Field Testing (NFT) inspects carbon steel internal process tube walls without fin interference.
Scans fin-fan tubes at speeds up to 1 m/s. Immune to external fin Geometry interference.
Why Near Field Testing (NFT) is Preferred for Fin-Fans
Near Field Testing uses transmit-receive eddy current coils operating at low frequency to scan internal carbon steel tube walls.
Key NFT Advantages
- Immune to external aluminum fin signals and fin-base corrosion geometry.
- High pull speed (up to 1.5 m/s) allows scanning thousands of fin-fan tubes per shift.
- Accurate detection of internal ID erosion, pitting, and wall loss under header boxes.
Primary Fin-Fan Damage Mechanisms
- Internal ID erosion-corrosion at tube inlet expansion zones.
- Atmospheric corrosion under fins in marine/coastal chemical environments.
- Header box shoulder plug gasket leaks and thread galling.
How B2B Project Workflow Works
From initial RFP scope to direct client sign-off. NDT EXCHANGE does not charge commissions or manage project payments.
RFP Scope
Asset Owner posts turnkey B2B inspection scope with technical specifications, asset list, and required NDT methods.
Competitive Bids
Certified NDT agencies submit competitive proposals (Fixed-Bid / T&M) detailing technician rosters and day rates.
Direct Settlement / Escrow
Client awards bid and sets up direct milestone payment or escrow — NDT EXCHANGE never holds or manages project funds.
Field Execution
Level II/III inspectors perform on-site testing (PAUT, TOFD, MFL, UT), capturing flaw data and calibration overlays.
Sign-Off & Payout
Level III auditor reviews findings; upon client sign-off, funds release directly to agency with 0% platform commission.