25mm Gr2 Titanium Tube-to-Tubesheet Fit: OD and Hole Tolerance, Clearance Window, Expansion Ratio and Tube-End Projection Dimension Chain

25mm Gr2 Titanium Tube-to-Tubesheet Fit: OD and Hole Tolerance, Clearance Window, Expansion Ratio and Tube-End Projection Dimension Chain

A 25 mm Grade 2 titanium condenser tube and a 25.4 mm one are nominally the same tube, and our 25 mm specification page already settles that equivalence, the OD tolerance it quotes as plus or minus 0.10 mm, the wall thickness range, straightness, expanding and welding, U-bending, composition, NDT and lead time. We treat all of that as a known input rather than restating it. Our ordering-by-failure-mode guide and our vibration and re-tube guide belong to the same first line: what the size is, what standard to buy it to and what the bundle will see in service. That page tells you what the size is and what standard to buy. This article starts where it stops: whether that OD actually assembles into the tubesheet hole. The two are independent check lines, not competing ones. A tube OD band stacked on a hole tolerance band produces a diametral clearance window, and that window, not the nominal 25 mm, decides whether the joint can be rolled and seal-welded.

At a Glance: Eight Decisions That Separate a Sealed Tube-to-Tubesheet Joint from a Weeper

Rows two and three carry most of the rework. Our B338 tube guide gives the product context and our 25 mm specification page fixes the OD band as a known input. A mill certificate can certify a heat; it cannot certify a clearance window it did not measure for your tubesheet. Read the rest as the second check line that starts where the certificate stops.

The Nominal-Equivalence Trap: 25 mm and 25.4 mm Are the Same Tube, Not the Same Hole

The purchasing equivalence between 25 mm and 25.4 mm is a statement about the tube, not about the drilled tubesheet. Our 25 mm specification page and our tube OD classification page settle the tube side as a known input. The hole is a separate manufactured feature with its own diameter tolerance, pitch and surface finish, called out on the tubesheet selection page and the drilling drawing. Treating the two nominal sizes as interchangeable at the hole is the trap: equivalent tube does not mean equivalent fit.

Our seamless B338 tube page and our custom-drilled baffle and tubesheet page show the two parts that must meet. The specification line fixes what was bought; the fit-up line fixes whether the OD band and the hole band leave a workable clearance. They are two independent check lines, and a pass on the first does not grant a pass on the second.

Nominal equivalence is a purchasing statement. A clearance window is a geometric result of two tolerance bands measured on the parts.

Where the Tolerance Goes: Stacking the OD Band on the Hole Band

The fit chain is one identity, not a spec table. Diametral clearance equals the measured hole diameter minus the measured tube OD at the same axial station, and each term carries its own tolerance band. The worst case is not two nominal numbers: it is a tube at the top of its OD band entering a hole at the bottom of the hole band, or the reverse. Written this way the arithmetic is deterministic. None of these terms is a supplier promise; they are quantities the shop must close with measurements on the delivered tube and the drilled plate.

Our tube-sheet welded joint detail shows the interface, and our tube weld and early-failure guide shows why rolled and seal-welded joints are sensitive to the starting gap. Our WPS and NDT qualification guide covers the weld procedure record. Name the drilling drawing revision and the hole tolerance callout before quoting any clearance number; where published bands disagree, we publish the conflict in chapter six.

The Dimension Nobody Measures: Expansion Ratio and Tube-End Projection

Two dimensions decide whether a tube that fits the hole stays sealed, and neither is the nominal OD. Expansion ratio describes how far the tube wall is thinned and the bore opened by rolling to close the clearance; published figures define it as wall-thickness reduction, bore growth or OD growth, so a single percentage is not portable. Tube-end projection is how far the tube stands past the tubesheet face before a seal weld, and the correct value depends on the joint detail. Our tube bundle assembly page and our cut-to-length tube page give the product and cut context; the drawing fixes the projection.

Projection and expansion form one dimension chain with the tubesheet thickness and the tube stick-out. Cut the tube short and the weld land disappears; roll too far and the wall thins into the tolerance floor. Our U-bent condenser tube page shows a formed end where the chain is fixed before the bundle is built. Measure both on a station log rather than from the cut list.

A cut list is a purchase input, not a fit result. Re-measure projection and wall after rolling against the joint detail before release.

Re-Drill or Ream? The Hole Bridge, the Pitch and the Span

Whether a substituted OD needs a re-drill

If a bundle is swapped from one nominal size to the other, the drilled hole is the fixed feature and the tube is the variable. A hole drilled and accepted for one OD band does not automatically accept a substituted band, because the clearance window recomputes. Our 25/32/50 mm OD stock page and our exchanger built to client drawing page show why the drilling drawing, not the stock list, decides. Ream only if the drawing revision and the remaining ligament allow it, otherwise the plate is re-drilled or rejected.

Ligament and hole-bridge width

The minimum bridge between adjacent holes is a function of pitch and hole diameter, not a fixed number. A hole enlarged for a different OD band consumes ligament, and a thin bridge distorts under rolling and leaks under pressure. Our drilled baffle and tubesheet page gives the drilling context and our titanium tube range lists the product. Confirm the pitch, the hole callout and the minimum ligament against the named drawing clause and code edition.

Re-tube span goes to the vibration line

After a re-tube, the unsupported span and the baffle spacing are a separate check that belongs to our vibration and re-tube guide, not to this fit-up line. We do not restate it here. This line closes at the hole, the clearance and the joint; the span check closes at the bundle dynamics. Both records are valid and are signed at different gates.

When the Published Clearance and Expansion Numbers Disagree: Publish the Conflict, Not One Value

Ask several sources for a tubesheet hole tolerance, an expansion ratio or a tube-end projection and you get a spread, not one table. Product standards, vessel codes, TEMA-class tables and rolling procedure notes use different definitions and different joint types. Presenting any one figure as correct would be false precision. The values below are the conflict, not the controlling number. The controlling value is the one measured on these parts and named in the drawing revision and the purchase order. Our OD classification page and our B338 guide are product references, not the governing clause.

Our 25 mm specification page gives the OD band as a known input and our heat exchanger mill certificate page shows the form of a traceable record. A chart is a buying aid; the measured clearance and the signed verification sheet are the tie breakers. Chapter ten gives six actions that settle the numbers.

Two Independent Check Lines: Fit-Up Geometry Here, Span and Pressure Tests Downstream

Whether a delivered tube passes receiving inspection, and whether a finished bundle passes a hydrostatic test, are separate questions. They belong to the receiving line and the test line that our tube receiving inspection page, our hydrostatic test guide and our tube weight calculator already cover. We do not restate those lines. This line decides whether the OD band and the hole band leave a clearance the joint can close. All are valid, they are checked at different gates, and a pass on one does not grant a pass on another.

Keep the records separate. The receiving file holds the purchase order, the certificate and the dimensional acceptance of the tube as delivered. The test file holds the pressure record after assembly. The fit-up file holds the drilling drawing revision, the paired OD and hole survey, the expansion basis, the projection log, the ligament check and the signed 14-line sheet. Our equipment leak repair guide is a downstream consequence, not a substitute for the fit-up record. When an enquiry asks about receipt we point to receiving; when it asks whether a substituted tube will seat in an existing plate, we work the clearance chain.

Limitations and Failure Conditions: Eight Tube-to-Tubesheet Fit-Up Rejection Triggers

[Geometry] Trigger 1 - Nominal 25 mm equated with 25.4 mm at an existing drilled hole

Recompute the clearance window from paired OD and hole readings rather than the nominal size. A purchase substitution that treats the two diameters as identical skips the band stack entirely. Judge against the drilling drawing revision and the measured hole. Our 25 mm specification page is a buying reference, not the fit record. In a dispute, rebuild the chain from the hole survey and photograph the tube end before rolling.

[Geometry] Trigger 2 - Tube OD and hole diameter quoted without their tolerance bands

Measure both features at mapped stations and carry the full band into the diametral clearance calculation. A nominal gap is incomplete fit-up evidence. Our OD classification page names the tube side and our drilled plate page names the hole side. In a dispute, re-survey the hole and the tube rather than the certificate.

[Geometry] Trigger 3 - Hole enlarged by reaming so the remaining ligament falls below the drawing bridge

Measure the tightest bridge between adjacent holes against the named code clause before and after any ream. An oversized hole consumes ligament and distorts under rolling. Our tube-sheet joint detail gives the interface. In a dispute, hold the plate and re-check pitch and hole diameter at every station.

[Fit] Trigger 4 - Clearance window outside the rolling procedure band so the joint will not seal

Compare the measured diametral clearance with the band in the named rolling procedure, then confirm by a trial roll on a witness coupon. A gap the roller cannot close becomes a weeper. Our weld and early-failure guide shows the downstream cost. In a dispute, re-pair the OD and hole readings and reset the expansion target.

[Fit] Trigger 5 - Expansion ratio defined inconsistently between the mill, the shop and the drawing

State whether the ratio means wall reduction, bore growth or OD growth, and measure the wall before and after rolling on the same definition. A percentage quoted without its definition is not portable. Our WPS and NDT qualification guide shows a signed procedure decision. In a dispute, re-qualify the roll and re-log the wall survey.

[Fit] Trigger 6 - Tube-end projection or recess not matching the joint detail before seal welding

Measure stick-out against the weld symbol and joint detail at each tube end, not from the cut list. A short tube loses the weld land; an over-long one disturbs the channel. Our cut-to-length tube page gives the cut context. In a dispute, re-measure projection and re-cut before welding.

[Process] Trigger 7 - Re-tube completed without forwarding the new span to the vibration check

Any change of OD, wall or support spacing resets the unsupported span that belongs to our vibration and re-tube guide. Issue the revised span and baffle layout to that line before the bundle is released. A fit-up pass does not cover bundle dynamics. In a dispute, hold the release until the span check is signed.

[Process] Trigger 8 - No paired OD/hole survey, no projection log or no signed verification sheet

Reconcile every tube and every hole against the drilling drawing revision, the expansion basis, the projection log and the signed 14-line sheet. A joint whose clearance map cannot be rebuilt is a reject regardless of a clean mill certificate. Our mill certificate page shows what the mill record proves. In a dispute, restore the hole-to-tube map before release.

The 14-Line Tube-to-Tubesheet Fit-Up & Dimension Chain Verification Sheet

Line five is often answered with two nominal numbers instead of paired readings, line six with a single gap instead of the limit case, line seven with an undefined percentage and line nine with a cut list rather than a measured projection. Our tube receiving page and our mill certificate page separate material evidence from fit-up work, and our hydrostatic test guide and our equipment leak repair guide show the downstream cost of an undocumented joint. A sheet without a signature column is a note, not an inspection record. Confirm every criterion against the drawing revision and the standard edition named in the purchase order.

Six Verification Actions When Hole, OD and Expansion Figures Conflict

1. Require every acceptance value to carry its document, revision and clause. Name the ASTM B338 or ASME SB-338 edition, the drilling drawing revision, the rolling procedure version and the code edition before quoting any clearance. Our B338 guide is a product reference, not the governing clause.
2. State the measured condition and method: tube OD and hole diameter from paired surveys at mapped stations, not the nominal figures. Our OD classification page gives the tube-side baseline.
3. Publish the fit chain before rolling: hole band, OD band, diametral clearance window, expansion target, projection and ligament. A calculation is a prediction; the paired survey is the record. Our tube weight calculator is a mass tool, not a fit tool.
4. Name who reviews the conflict: buyer quality, fabricator engineer, welding inspector and, where the contract calls for it, a design engineer, with authority to accept or hold. Our WPS qualification guide shows qualification is a signed decision.
5. Keep records independent with their own dates: purchase order and MTC, paired OD and hole survey, rolling coupon, wall survey, projection log, ligament check and the signed verification sheet. Our mill certificate page covers what the mill record proves.
6. Use trigger-based re-verification: any OD substitution, ream, re-drill, re-roll, procedure change or opened hold forces reassessment and a new span check. Our exchanger built to drawing page and our leak repair guide show the downstream cost.

Most of these cost nothing at planning and a great deal after a bundle is rolled and welded. Ask for the drilling drawing revision, the paired OD and hole survey, the rolling coupon, the projection log and the signed verification sheet for the same bundle. We are a stockholder, not the author of your drawing; where figures come from published guides we label them, and where they disagree we give the disagreement and the action. Our hydrostatic test guide is a later gate, not a substitute for the fit-up record. Confirm the governing criterion against the drawing revision and the standard edition in the purchase order.

Summary: Choose a Ream-and-Re-Roll if, Choose a Re-Drill or Reject if

Choose X if: a ream-and-re-roll with a signed verification sheet

• The drilling drawing revision, the hole tolerance callout and the tube OD band are named, and paired readings give a closable clearance window.
• An expansion ratio with its definition, a wall survey and a projection log are measured against the joint detail.
• The remaining ligament is at or above the named minimum after any ream, and the rolling procedure band is met.
• The 14-line sheet is signed per line, and the re-tube span has been forwarded to the vibration line.

Escalate to a fit-up hold or a drawing review if:

• A clean mill certificate is the only fit-up evidence offered.
• A 25 to 25.4 mm substitution was accepted at an existing hole without recomputing the clearance window.
• Published hole, clearance or expansion figures disagree and no one has named the governing edition.
• The projection, the ligament or the expansion target was taken from a cut list or a single reading.
• The paired OD and hole survey, the projection log or a signed verification sheet is missing.

Choose Y if: a re-drill or a rejected plate

• The hole band and the substituted OD band leave no closable clearance; re-drill or reject rather than over-roll. Our OD stock page covers the sizes that make this common.
• Reaming would consume the minimum ligament, so the drawing bridge cannot be held. Our tubesheet selection page gives the plate context.
• The buyer cannot produce a paired OD and hole survey or a signed sheet; set up the shop records first.
• The re-tube span is in dispute; keep that on the vibration line and read our vibration and re-tube guide while the fit-up line stays independent.

The whole subject reduces to one sentence: a nominal size is not a fit, because the drawing tells you what to order while the tolerance chain tells you whether the tube will seat in the hole. When you enquire, send the tube OD band, the drilled hole callout, the pitch, the joint detail, the drawing revision and the paired survey. We are a Baoji China Titanium Valley titanium stockholder with roughly 800 tonnes in stock, about 80 tonnes of it in tube. We cut to non-standard and small-batch sizes, work from customer drawings, read and certify to ASTM, ASME and GB standards, export-pack in house, and dispatch confirmed in-stock orders the same day. Send us the drilling drawing and the paired survey, and we will tell you what we can ship and which decisions belong with your team. Request a quote →

Frequently Asked Questions

Are 25 mm and 25.4 mm Gr2 tubes interchangeable in an existing tubesheet?

No. The two diameters are nominally the same tube, but the drilled hole is a separate feature with its own tolerance band. A hole drilled and accepted for one OD band does not automatically accept a substituted band, because the diametral clearance window recomputes. Measure the tube OD and the hole diameter at mapped stations, subtract them as a pair and compare the window with the named rolling procedure before any substitution. The fabricator engineer signs that check against the drilling drawing revision.

How is the tube-to-tubesheet clearance window actually calculated?

It is a paired measurement, not a nominal subtraction. Diametral clearance equals the measured hole diameter minus the measured tube OD at the same axial station, and both terms carry tolerance bands. Check the worst case as well: a tube at the top of its OD band in a hole at the bottom of the hole band. Name the drilling drawing revision and the hole tolerance callout, and record the paired survey. The fabrication inspector logs the local extremes rather than a single gap.

When a tube is substituted, must the tubesheet be re-drilled?

Only if the recomputed clearance and the remaining ligament allow no other route. Reaming an existing hole to a larger band consumes the bridge between holes and may fall below the named minimum, so the decision is a drawing one, not a shop convenience. Recompute the clearance window, measure the tightest ligament and sign a re-drill, ream or reject decision against the drilling drawing revision. A fit-up pass does not by itself authorise a re-drill.

Does a clean mill certificate prove the tube will fit the tubesheet?

No. A certificate proves the tube OD band, wall and heat as delivered; it does not measure the drilled hole or the resulting clearance. Fit-up evidence is the paired OD and hole survey, the expansion basis, the projection log, the ligament check and the signed 14-line verification sheet. These are two independent check lines at different gates. A tube can be on certificate and still leave an unclosable gap in an existing plate.

Why do published expansion ratios and tube-end projections conflict?

Because sources define them differently. Expansion ratio is variously wall-thickness reduction, bore growth or OD growth, and acceptor bands differ for rolled-only versus rolled-and-welded joints. Projection depends on whether the joint is expanded, seal-welded or strength-welded. We publish the conflict rather than one figure. Name the rolling procedure version and the joint detail, measure wall before and after rolling and measure projection per tube end. The welding inspector signs both.

Who signs off the paired OD and hole survey before rolling starts?

The fabrication inspector signs the paired OD and hole survey and station map against the drilling drawing revision and the measurement plan, the welding inspector signs the expansion target and projection log against the rolling procedure and joint detail, and the fabricator engineer signs the ligament check against the code edition. A single reading is not a survey: measure at mapped stations because both the OD band and the hole band vary across the bundle.

Is the fit-up check the same as the receiving inspection or the hydrostatic test?

No. They are independent lines at different gates. Receiving decides whether the delivered tube meets its OD and wall band, and the hydrostatic test decides whether the finished bundle holds pressure; neither measures the clearance window at the hole. The fit-up line uses the drilling drawing revision, the paired survey, the expansion basis, the projection log, the ligament check and the signed sheet. A pass on one does not grant a pass on another.

Send us these 6 points (or just attach your drawing / old supplier spec)

Not sure how to fill this? Send your drawing or an old supplier's specification sheet — we will break it down for you.

Why buyers come to us

Stock holder in Baoji Titanium Valley with ~800 t inventory · cut-to-size and small batch · drawing-based machining for non-standard parts · we read ASTM / ASME / GB specs · export experience · same-day response on quotes.