Heat Exchanger Manufacturing Process: How a Shell-and-Tube Unit Is Built, Step by Step

Quick Answer

A shell-and-tube heat exchanger is built in a fixed sequence: design and drawing approval; material receipt and traceability checks; cutting and rolling the shell courses, held to an out-of-roundness of no more than 1% of the nominal diameter under ASME Section VIII Division 1 (UG-80); welding and radiographing the seams; forming and machining heads, cones and flanges; drilling tubesheets and baffles; assembling the shell and nozzles; building the tube bundle and making the tube-to-tubesheet joints; post-weld heat treatment where code or service demands it; hydrostatic testing, which under ASME Division 1 is 1.3 × MAWP corrected for temperature; and final inspection, painting, nameplate and data book. For a custom TEMA Class R unit, 16 to 30 weeks from order to dispatch is common, and the critical path is usually material — forgings, tubes and impact-tested plate — rather than shop hours. The stages a buyer should witness are material review, shell and bundle fit-up, tube-to-tubesheet joint testing and the hydrostatic test.

Every photograph in this article was taken during one Kasko Makine order: four shell-and-tube units, tagged 005, 006, 007 and 013 on the shop floor, caught at the stage where they are still parts rather than heat exchangers. Rolled shell courses with chalked radiography results. Ellipsoidal heads carrying temporary lifting lugs. A cone on the submerged-arc station. Forged rings that will become body flanges, and a stack of drilled plates that will hold the tubes in line.

Buyers usually see a heat exchanger twice: as a data sheet at enquiry, and as a painted unit on a trailer. Everything that decides whether it will run for twenty years happens in between, and most of it is invisible once the paint goes on.

This article walks through that in-between in the order the shop works, and at each stage notes what a buyer should check.

Before Any Steel Is Cut: Design, Drawings and the ITP

Thermal design sets the geometry

The thermal design — normally run in specialist rating software against the process data sheet — fixes the things that shape fabrication: shell diameter, tube count, tube length, number of passes, baffle type, cut and spacing, and nozzle sizes. If the data sheet is incomplete or the design conditions are vague, this is where the project quietly goes wrong. Our guide to TEMA data sheets covers how to fill one in properly.

Mechanical design sets the thicknesses

The mechanical design takes the geometry and applies a pressure code:

• ASME Section VIII Division 1 — the most widely specified, with the ASME Certification Mark and "U" designator where the purchaser requires a stamped vessel
• EN 13445 — the European unfired pressure vessel standard, typically used with the Pressure Equipment Directive (2014/68/EU) for installation in the EU
• AD 2000-Merkblätter — the German code, still common in German-engineered plants
• National standards such as ČSN 69 0010 and STN 69 0010 in the Czech Republic and Slovakia

On top of the pressure code sits TEMA, which governs heat-exchanger-specific construction — tube pitch, baffle rules, tubesheet details, clearances, tolerances. TEMA Class R is the refinery and severe-service class and the default for petroleum and petrochemical duty; Class C covers general commercial service; Class B covers chemical process service. Petroleum projects frequently add API 660 as a further layer of requirements.

Drawing approval

Before material is ordered, the fabricator issues for approval a general arrangement drawing (nozzle orientation, projections, supports, weights, lifting points), the main detail drawings, the calculation package, a weld map with the welding procedures assigned to each joint, and an inspection and test plan.

Approval is where weeks are won or lost. A two-week review cycle is realistic; three rounds of comments is not unusual. The expensive changes are the late ones — a nozzle moved or added after plate and forgings have been ordered resets part of the material schedule.

The inspection and test plan (ITP)

The ITP lists every inspection activity and who attends it. Each line is marked:

• H — Hold point. Work stops until the nominated inspector has attended or formally waived. Fit-up of critical seams and the hydrostatic test are typical hold points.
• W — Witness point. The inspector is notified and may attend; work proceeds if they do not.
• R — Review. Documents are reviewed — material certificates, NDE reports, heat treatment charts.

On an ASME-stamped unit, the Authorized Inspector from an Authorized Inspection Agency has their own mandatory involvement in addition to the purchaser's inspector. Agree the ITP before fabrication starts, not after the first hold point has been missed.

Step 1: Materials — Receipt, Verification and Traceability

Material is checked on receipt against the approved drawings and the purchase specification, not just against the delivery note:

• Grade and condition. SA-516 Grade 70 normalized is not the same material as SA-516 Grade 70 as-rolled for impact purposes. The heat treatment condition on the certificate matters.
• Impact testing. If the minimum design metal temperature (MDMT) requires it, the certificate must show Charpy results at the right temperature. Low-temperature carbon steels — for example SA-333 Grade 6 pipe and SA-350 LF2 Class 1 forgings — are bought impact-tested by specification.
• Supplementary requirements. Sour service may add HIC testing, hardness limits and carbon-equivalent limits; hydrogen service may add chemistry restrictions for Cr-Mo steels.
• Certificates. EN 10204 type 3.1 as a minimum, 3.2 where third-party verification is specified. Our guide to EN 10204 3.1 vs 3.2 certificates explains the difference.
• Positive material identification (PMI) on alloy components, by XRF or optical emission, to confirm that what arrived is what the certificate says.

Traceability starts before the first cut. The heat number, material grade and order number are transferred onto every piece before the plate or pipe is cut, so that the identity survives the cutting. The nozzle-neck pipe pieces in the photograph below are paint-marked exactly this way. Lose that marking and the piece becomes scrap, however good the steel.

Why material is the critical path. Forgings for body flanges and tubesheets, impact-tested plate and special tube grades routinely carry lead times of 8 to 16 weeks or more, against perhaps 6 to 10 weeks of actual shop work. Orders placed the day drawings are approved are the single biggest schedule lever a buyer controls.

Step 2: Shell Courses — Cutting, Rolling and Longitudinal Seams

Small exchanger shells are often made from seamless or welded pipe, up to around NPS 24 (600 mm). Above that, shells are rolled from plate.

Cutting and edge preparation. The plate is cut to the developed length — circumference at the mean diameter, with allowance for the weld gap — and the edges are bevelled for the longitudinal seam.

Pre-bending. Plate rolls cannot curve the last part of each edge, so the edges are pre-bent first. Skip this and the finished course has flats either side of the seam, which no amount of welding corrects.

Rolling. Three-roll or four-roll plate bending machines roll the plate into a cylinder. Thick plate is rolled in several passes, checking diameter with templates.

Longitudinal seam. Thick seams are normally welded by submerged arc welding (SAW), with run-on and run-off tabs so the start and stop are outside the finished seam. Where the code or specification requires impact testing of welds, production test plates are welded as an extension of the seam itself, so they represent the actual weld.

Radiography. The seam is then examined. Under ASME Division 1 the degree of radiography sets the joint efficiency used in the thickness calculation — 1.0 for full radiography, 0.85 for spot, 0.70 for none on a double-welded butt joint — so the examination level is a design decision, not just a quality one. The chalked "RT-OK" on the shell courses in the photograph is exactly that record: the seam has been radiographed and accepted before the course moves on. Ultrasonic examination, including phased array and TOFD, is accepted as an alternative to radiography under defined conditions.

Roundness. ASME limits out-of-roundness to 1% of the nominal diameter. For a heat exchanger that is not the binding constraint — TEMA's shell tolerances are tighter, because a bundle with baffles a few millimetres smaller than the shell has to slide through it. Courses are re-rounded after welding where needed.

Seam staggering. When courses are joined, the longitudinal seams of adjacent courses are offset from each other — ASME requires at least five times the thickness of the thicker plate unless the intersection is radiographed — so that seams never line up into a continuous weld line.

Shell rolling, cones and nozzle design are covered in depth in our guide to heat exchanger shells, cones and nozzles.

Step 3: Cones and Transitions

Cones join sections of different diameter. In heat exchangers the classic example is the kettle reboiler, where the shell enlarges from the bundle diameter to a larger vapour-disengagement shell. Cones also appear as reducers between channels and shells and on vertical units.

A cone is cut from a developed blank — an annular sector — and rolled on the plate bending machine with the rolls set to produce the taper. The longitudinal seam is then welded, typically by submerged arc, as on the 006 cone in the photograph.

The design point that matters is the junction. Where a cone meets a cylinder, the change in direction of the wall creates a discontinuity stress, and ASME requires a reinforcement check at both the large and small ends for cones with a half-apex angle up to 30°. Steeper cones need a knuckle — a toriconical transition — or a more detailed analysis.

Step 4: Heads

Heads are usually bought from specialist head manufacturers and arrive formed but unmachined. The 2:1 ellipsoidal head is the default for exchanger shells and channels; torispherical heads (ASME flanged and dished, or the European Klöpper and Korbbogen types) and hemispherical heads have their own places. Our guide to pressure vessel heads compares them in detail.

What happens to a head in the fabrication shop:

• Thickness check. Forming thins the plate, so heads are ordered by minimum thickness after forming, and that minimum is verified by ultrasonic thickness measurement on receipt.
• Shape and circumference check. The head's circumference must match the shell's closely enough to meet the code's alignment limits at the circumferential seam.
• Machined weld bevel. The straight flange is machined to the weld preparation — the bright ring at the rim of a finished head.
• Nozzle openings. Openings are machined, not just flame-cut, so the nozzle fits with a controlled gap and bevel. Large heads are clamped on a horizontal boring mill for this, as in the second photograph.
• Temporary lugs. The steel lugs welded around the heads are for handling and fixturing. They must later be removed, ground flush and checked by magnetic particle or dye penetrant examination, because the weld spots are potential crack sites.

Cold-formed heads may require heat treatment after forming, depending on material, thickness, the forming strain and whether impact testing is required. That is a head-supplier and code question that should be settled at order, not discovered at final inspection.

Step 5: Flanges, Nozzles and Forgings

Body flanges. The large flanges that join channel to shell, or shell to shell cover, are not catalogue flanges. They are designed for the specific diameter, pressure and gasket, and made from forged rings like those in the photograph, then machined to the drawing — including the gasket face, whose surface finish has to suit the gasket type. Spiral-wound gaskets, for instance, are normally seated on a finish in the region of 3.2 to 6.3 µm Ra.

Nozzles. A typical process nozzle is a weld-neck flange on a pipe neck, set into the shell or head and welded with full penetration. Heavier designs use long weld-neck or forged self-reinforced nozzles. Where the shell or head needs extra reinforcement around an opening, a reinforcing pad is added, with a tell-tale hole so that a leak in the pad weld can be detected and the space can vent during heat treatment.

Small connections. Vents, drains, instrument and thermowell connections are usually forged couplings or small weld-neck nozzles.

Orientation and projection. Every nozzle is set out to the orientation and projection on the general arrangement drawing. This is a classic witness-point check, because a nozzle 15 degrees out or 20 mm short does not line up with the piping — and piping is rarely redesigned to suit the exchanger.

Step 6: Tubesheets and Baffles

The tubesheet is the most precise component in the exchanger. It is drilled on CNC deep-hole drilling machines, and the hole diameter, the position of every hole and the drift of the drill through the thickness are all controlled — TEMA specifies the permitted tolerances. For expanded tube joints the holes are usually grooved, so that the expanded tube locks into the grooves.

Baffles are drilled to the same pattern so that every hole lines up through the bundle; shops commonly clamp baffles into a stack and drill them together. The blank band across the hole pattern of the plates in the photograph is the pass-partition lane: no tubes are placed there because, in a multi-pass exchanger, that line is where the pass partition plate in the channel seats against the tubesheet.

Tubesheet design, layout, pitch, baffle cut and spacing and tube-to-tubesheet joints are covered in our guide to tubesheets, baffles and tube bundles.

Step 7: Shell Assembly

The courses, cones, body flanges and heads are fitted up and joined by circumferential seams. Shells are mounted on turning rolls — the powered rotators in the photograph — so the circumferential seam rotates under a fixed welding head and can be welded in the flat position, usually by submerged arc.

Then the nozzles are set out, fitted and welded, and the shell is checked:

• Inside surface. Internal weld reinforcement is ground flush wherever the bundle has to pass. A proud weld bead will stop a bundle as effectively as an undersized shell.
• Bundle clearance. Many shops pull a gauge disc the diameter of the baffles through the completed shell before the bundle goes anywhere near it. It takes an hour and has saved many shops a very bad week.
• Straightness and overall dimensions against the general arrangement drawing.

Seams are examined by radiography or ultrasonic testing as required, and nozzle welds by magnetic particle or dye penetrant and, where specified, ultrasonic examination.

Step 8: Tube Bundle Assembly and Tube-to-Tubesheet Joints

Building the skeleton. Tie rods are screwed into the stationary tubesheet, and the baffles are threaded onto them with spacer tubes between, building a rigid cage at the correct baffle spacing.

Inserting the tubes. Tubes are pushed through the tubesheet and every baffle, usually by hand with a nose cone on the leading end to protect the holes. For a fixed-tubesheet unit the second tubesheet goes on next; for a U-tube unit the U-bends are already formed; for a floating-head unit the floating tubesheet is fitted.

Making the joints. Tubes are fixed into the tubesheet by expansion, by welding, or by both:

• Expanded joints — the tube is rolled or hydraulically expanded into the hole, and into the grooves, by a controlled amount
• Seal-welded and expanded — a small weld provides leak tightness; the expansion carries the load
• Strength-welded — the weld carries the load, often with a light expansion to close the crevice

Welded tube-to-tubesheet joints are normally qualified on a mock-up under ASME Section IX before production welding. Division 1 also accepts a conventional groove-weld qualification, but owner specifications for critical service commonly insist on the mock-up — and expansion procedures are qualified the same way on critical units. The sequence — whether tubes are welded before or after final expansion — is part of the qualified procedure, not a shop preference.

Testing the joints. Before the hydrostatic test, tube joints are usually leak tested on their own, commonly with low-pressure air and a soap solution, or by helium leak testing where the fluid is toxic or the specification is strict. Finding a leaking joint at this stage takes minutes to repair. Finding it at hydrotest means draining, drying and repeating.

Step 9: Post-Weld Heat Treatment

PWHT is required by the code above certain thicknesses — for ordinary carbon steel under ASME Division 1, generally above 38 mm, and above 32 mm unless a minimum preheat is applied during welding — and for alloy steels at lower thicknesses. It is also frequently required by the service, regardless of thickness: amine, caustic, wet H₂S and hydrogen services are the usual examples, and the owner's specification governs.

Sequence matters in a heat exchanger. Heat treatment relaxes expanded tube joints, so wherever possible the welds that need PWHT are completed and treated before the tubes are expanded. Where tube-to-tubesheet welds themselves need PWHT, final expansion follows the heat treatment.

Whole units are treated in a furnace; local PWHT with electrical heating bands is used for closing seams and repairs. Either way, the temperature charts from thermocouples on the part become part of the data book.

Step 10: Pressure Testing

Under ASME Section VIII Division 1 the hydrostatic test pressure is 1.3 × MAWP, multiplied by the ratio of the material's allowable stress at test temperature to that at design temperature. The joints are then inspected at a reduced pressure, in the region of the MAWP, rather than at full test pressure. The 2025 edition of Division 1 rewrote the testing paragraphs, so check the wording of the edition the unit is built to. Other codes use different factors — EN 13445 and AD 2000 have their own formulas — so the test pressure is calculated per code, not copied from the last job.

Test sequence. A heat exchanger has two pressure spaces, and the sequence is designed so that every joint is visible while it is under pressure:

1. Shell-side test with the tube ends exposed. For a floating-head exchanger this needs a test ring that seals the floating tubesheet to the shell so the channel and floating head cover can stay off. For U-tube units a test flange or gland seals the shell against the tubesheet. Any leak at a tube joint shows directly.
2. Tube-side test with channels and covers fitted, pressurising the tubes.
3. Final shell-side test with all covers fitted, where the design requires it.

Fixed-tubesheet units are simpler: the shell-side test pressurises around the tubes, and the tube ends can be watched with the channel or bonnet removed.

Test hardware. Test rings, test flanges and test blinds are designed for the test pressure and the specific exchanger — machined blind covers like those in the photograph close nozzles and openings while the unit is under test. Kasko Makine supplies dedicated equipment for pressure testing heat exchangers.

Practical rules that prevent damage:

• Test water for austenitic stainless steel is chloride-controlled — commonly 50 ppm or less — and the unit is drained and dried promptly afterwards
• Metal temperature during the test is kept comfortably above the MDMT; ASME recommends at least 17°C (30°F) above it
• All air is vented from high points before pressurising
• Gauges are calibrated and of a suitable range, and the test pump has relief protection

Step 11: Final Inspection, Painting, Nameplate and Data Book

Final inspection checks overall dimensions, nozzle orientation and projection, flange faces, internal cleanliness and dryness, and that all temporary attachments are gone.

Painting and preservation. Surface preparation and coating follow the specified system. For shipping and storage, flange faces are protected, openings closed with blind flanges and gaskets, and the interior is often dried and blanketed with a small positive nitrogen pressure or protected with desiccant or vapour-phase inhibitor. Long sea voyages and months on a construction site corrode an unprotected bundle surprisingly fast.

Nameplate. The nameplate carries the code data — MAWP for each side, design temperatures, MDMT, test pressures, year, serial number and, for an ASME unit, the Certification Mark with the U designator and National Board number where registered.

The data book. The manufacturer's data book is the permanent record of the exchanger and typically contains:

• Approved drawings and design calculations
• Material certificates traceable to the heat numbers on the parts
• Welding procedure specifications, procedure qualification records and welder qualifications — see our guide to WPS, PQR and welder qualification
• NDE reports: radiography or ultrasonic, magnetic particle, dye penetrant, PMI, hardness
• PWHT charts
• Tube-to-tubesheet mock-up and leak test records
• Hydrostatic test reports and gauge calibration certificates
• The manufacturer's data report — for an ASME Division 1 shell-and-tube exchanger, Form U-1 with its shell-and-tube supplement, Form U-5 — or the EU declaration of conformity
• Nameplate photograph or rubbing

Agree the data book index at kickoff. Records that were never generated cannot be produced at the end.

Typical Timeline for a Custom Shell-and-Tube Unit

These are typical ranges for carbon steel and stainless units of moderate size. Alloy, clad, high-pressure and very large units take longer.

What Buyers Should Witness

1. Material review — certificates against the specification, including impact tests and heat treatment condition
2. Fit-up of critical seams — especially shell-to-tubesheet and body flange welds
3. NDE results — radiography or UT acceptance before closing seams
4. Bundle clearance — the gauge-disc or trial insertion through the shell
5. Tube-to-tubesheet mock-up and production leak test
6. Hydrostatic test — each stage of the sequence, with the tube ends visible
7. Final dimensional inspection and data book review before release for shipment

Common Specification Mistakes

1. Changing nozzles after drawing approval. A moved or added nozzle after plate and forgings are ordered costs weeks, not hours.

   Prevention: Freeze nozzle orientation, sizes and ratings with the piping designer before approving the general arrangement drawing.

2. No MDMT on the data sheet. Material is bought without impact testing, and the omission surfaces at certificate review — after the plate has been rolled.

   Prevention: State the MDMT and its coincident pressure on the data sheet, and require Charpy results on certificates where the code calls for them.

3. "Built to ASME" without saying what that means. Stamped or unstamped, Authorized Inspector involvement, National Board registration — these change cost, schedule and documentation.

   Prevention: Specify the code, edition, stamping and registration requirements explicitly — and for EU installation, state the PED conformity route.

4. No hold point for the tube-joint leak test. Leaking joints are found at hydrotest, after the unit has been filled.

   Prevention: Put a separate tube-to-tubesheet leak test into the ITP as a hold point, before the hydrostatic test.

5. Heat treatment in the wrong order. Tubes are expanded, then the unit is heat treated, and the expanded joints relax.

   Prevention: Review the fabrication sequence with the shop at kickoff and confirm that PWHT precedes final expansion.

6. No check of bundle-to-shell clearance before insertion. A proud weld bead or an out-of-round course stops the bundle halfway in.

   Prevention: Require internal seams to be ground flush where the bundle passes, and a gauge-disc pull-through as a witness point.

7. Test hardware planned late. The unit is ready, but the test ring or test blinds have not been made, and the hydrotest waits.

   Prevention: Order test rings, test flanges and blinds with the main materials — they are part of the exchanger's scope.

8. Untreated test water on stainless steel. High-chloride water left in an austenitic unit after testing initiates pitting and stress corrosion cracking before the unit is ever commissioned.

   Prevention: Specify maximum chloride content for test water, and drying immediately after the test.

9. Data book defined at the end. The buyer asks for records that were never generated.

   Prevention: Agree the data book index and document formats at kickoff.

10. No preservation specification for shipping and storage. Bundles corrode during a long voyage or months of site storage.

    Prevention: Specify drying, nitrogen blanketing or desiccant, flange face protection and inspection intervals during storage.

Supply from Kasko Makine

Heat exchangers

Kasko Makine manufactures custom tubular heat exchangers — coolers, heaters and condensers — in all the basic tubular configurations:

• U-tube exchangers
• Floating-head exchangers
• Fixed tube plate (fixed tubesheet) exchangers
• Tube-in-tube (double-pipe) exchangers
• Units built to special customer requirements

Design basis

• Predominantly TEMA Class R construction
• Pressure codes: ASME, AD 2000-Merkblätter, EN 13445, ČSN 69 0010 and STN 69 0010
• Materials to EN, ASTM, DIN and other international standards: carbon steels including low-temperature grades, alloy steels and austenitic stainless steels

Demanding services

• Heat exchangers resistant to hydrogen attack for hydrogen service
• Units for hydrorefining and catalytic reforming
• Exchangers for hydrocracking plant
• Heat exchangers for rapid cooling of cracked gases

Pressure test equipment

• Test rings, test flanges, test blinds and custom test jigs for heat exchangers, built to TEMA R, EN, GOST and ASME requirements — see equipment for pressure testing

Associated supply

• Heat exchanger gaskets for body flanges, channel covers and pass partitions
• Replacement tubes, tube bundles and spare parts
• Flanges, stud bolts and fittings for the connecting piping

Engineering support

Send the TEMA data sheet — or the process data if no data sheet exists yet — together with the design code, MDMT, any service-specific requirements and the destination. We will return the proposed construction, materials, a fabrication schedule with the material critical path identified, the inspection and test plan structure, and a quotation.

Certification

Material certificates to EN 10204 3.1 or 3.2, welding procedure and welder qualifications, NDE reports, PWHT charts, tube-to-tubesheet mock-up and leak test records, hydrostatic test certificates, and the code data report or declaration of conformity, compiled into a complete data book. Third-party inspection by the purchaser's nominated agency is accommodated at the agreed hold and witness points.

Logistics

Units are built in Europe and shipped as breakbulk or on flat-rack containers by road and sea, with lifting and sea-fastening plans, to Caspian, Middle Eastern, African and Central Asian destinations.

Send your TEMA data sheet and we will return a fabrication schedule and quotation within five working days. Reach us at info@kaskomakine.com or WhatsApp +90 (537) 521 1399.

Continue Reading: Heat Exchanger Series

• Shell and Tube Heat Exchangers: TEMA Types and Configurations
• Pressure Vessel Heads: 2:1 Ellipsoidal vs Torispherical vs Hemispherical
• Tubesheets, Baffles and Tube Bundles
• Heat Exchanger Shells, Cones and Nozzles
• TEMA Data Sheets: How to Specify a Heat Exchanger

Frequently Asked Questions

Q: How is a shell-and-tube heat exchanger manufactured?
A: Fabrication follows a fixed sequence: design and drawing approval, material receipt and traceability checks, cutting and rolling shell courses, welding and radiographing seams, forming and machining heads, cones and flanges, drilling tubesheets and baffles, assembling shell and nozzles, building the tube bundle and making tube-to-tubesheet joints, heat treatment where required, hydrostatic testing, then final inspection, painting, nameplate and data book.

Q: How long does it take to manufacture a custom heat exchanger?
A: A custom TEMA Class R shell-and-tube unit commonly takes 16 to 30 weeks from order to dispatch. Material procurement is usually the critical path — forgings, special tubes and impact-tested plate often take 8 to 16 weeks or more — while actual shop work is typically 6 to 10 weeks. Alloy, clad, high-pressure and very large units take longer.

Q: What is the hydrostatic test pressure for a heat exchanger?
A: Under ASME Section VIII Division 1 the hydrostatic test pressure is 1.3 times the MAWP, multiplied by the ratio of the material's allowable stress at test temperature to that at design temperature, and the joints are then inspected at a reduced pressure close to the MAWP. EN 13445 and AD 2000 use their own formulas, so the pressure must be calculated per the code of construction.

Q: Why is a test ring needed to hydrotest a floating-head heat exchanger?
A: A test ring seals the floating tubesheet to the shell so the shell side can be pressurised with the channel and floating head cover removed. That leaves the tube ends and tube-to-tubesheet joints visible during the shell-side test, so any leaking joint can be seen and repaired directly. U-tube units use a test flange or gland for the same purpose.

Q: What documents should come with a new heat exchanger?
A: The data book typically contains approved drawings and calculations, material certificates traceable to heat numbers, welding procedures and welder qualifications, NDE reports, PWHT charts, tube-to-tubesheet mock-up and leak test records, hydrostatic test reports with gauge calibrations, the code data report — ASME Form U-1 with the Form U-5 shell-and-tube supplement, or an EU declaration of conformity —, and a nameplate record.

Q: Which fabrication stages should a buyer witness?
A: The highest-value witness and hold points are material certificate review, fit-up of critical seams such as shell-to-tubesheet welds, NDE acceptance before seams are closed, the bundle-to-shell clearance check, the tube-to-tubesheet mock-up and production leak test, each stage of the hydrostatic test sequence, and final dimensional inspection with data book review before release.

Q: Why must post-weld heat treatment be done before tube expansion?
A: Heat treatment relaxes the residual contact stress that holds an expanded tube in its tubesheet hole, so expanding first and heat treating afterwards can leave the joints loose and leaking. Fabricators therefore complete and heat treat the welds that need PWHT before final tube expansion, and where tube-to-tubesheet welds themselves require PWHT, final expansion follows the heat treatment.