Refining / Heat Exchange

Refinery Hydrotreater Heat Exchanger Retube — 321 & 2205 U-Tubes

Saudi Arabia22+ tons321 Stainless Steel Seamless U-Tubes + 2205 Duplex Pipes

Project Background

A major refinery in Saudi Arabia operates a naphtha hydrotreating unit where the feed/effluent heat exchanger originally used carbon steel tube bundles. After 5 years of service at 350°C in H₂S-rich environment, severe sulfidic corrosion caused tube wall thinning exceeding 0.3 mm/year. During a planned 45-day shutdown window, the owner needed complete retubing of 4 heat exchangers with upgraded materials to extend run length between turnarounds.

Technical Specifications

Grade	ASTM A213 TP321 Seamless U-Tubes; UNS S32205 Seamless Pipes
Size Range	OD 19.05 – 38.1 mm (3/4" – 1-1/2"), multiple U-bend radii
Standards	ASTM A213, TEMA Class R, API 660, NACE MR0103
NDE Requirements	Post-bend solution anneal + 100% Eddy Current + per-tube hydro (1.5× design P)

The Challenge

U-tube bending introduces cold work residual stresses and sensitization risk in stainless steels. If not properly post-bend heat treated, this leads to stress corrosion cracking in H₂S service and reduced intergranular corrosion resistance — both unacceptable for refinery heat exchanger reliability.

TOKO TECH Solution

TOKO TECH performed secondary solution annealing (940°C ± 10°C / rapid cooling) on all 321 U-tubes after bending to eliminate cold work residual stresses and restore intergranular corrosion resistance. For the high-temperature H₂S section, 2205 duplex tubes were supplied, leveraging the duplex microstructure's superior resistance to stress corrosion cracking and significantly increasing operational safety margins.

Search Keywords

321 U-tubeheat exchanger retubingrefinery hydrotreaterNACE MR0103 tubeduplex heat exchanger tubesulfidic corrosion resistant tube

Frequently Asked Questions

Why do U-tubes need post-bend heat treatment?

Cold bending introduces residual stresses and can sensitize austenitic stainless steels by precipitating chromium carbides at grain boundaries. Post-bend solution annealing (typically 940°C for 321) dissolves these carbides and relieves residual stresses, restoring the tube's resistance to intergranular corrosion and stress corrosion cracking.

What is the difference between NACE MR0175 and NACE MR0103?

NACE MR0175 applies to upstream oil & gas production equipment in sour (H₂S) service. NACE MR0103 applies to petroleum refining environments where H₂S is present but under different process conditions. Both standards specify material hardness limits and heat treatment requirements to prevent sulfide stress cracking, but MR0103 is specifically tailored for refinery downstream applications.

How fast can a heat exchanger retube be completed?

A typical shell-and-tube heat exchanger retube can be completed within a 4-6 week shutdown window with proper planning. TOKO TECH supports accelerated delivery by maintaining strategic inventory of common U-tube sizes and materials, and by coordinating directly with the site team to sequence tube deliveries matching the bundle extraction and installation schedule.

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