Direct answer: Choose nitric-acid cooler-condenser tubing from the conditions at the tube wall, not acid concentration alone. 304L can be a practical baseline; controlled nitric-acid-grade stainless steel, Alloy 690 or zirconium may warrant evaluation when temperature, reboiling or contamination changes the corrosion risk. None is a universal upgrade. Confirm liquid, vapour, condensate, weld and cooling-water conditions, then qualify the proposed tube condition and acceptance plan before ordering. [1][2][3]
DAXUN / TECHNICAL PROCUREMENT
Locate the controlling exposure, compare defined material conditions and qualify the tube you intend to order.
Locate the damage before selecting the replacement alloy
The first selection decision is which part of the cooler-condenser needs a different material and why. An acid-side inlet, a condensing region, a tube end and a water-side deposit can present different environments within the same exchanger. Replacing every tube with a more expensive alloy without identifying the controlling location can leave the original failure mechanism unresolved.
For an existing unit, collect the damaged-tube position, wall-thickness findings, operating history and available examination report. Record whether attack began on the inside or outside and whether it is uniform, concentrated around a joint, or associated with deposits. These observations do not establish a mechanism by themselves, but they make the subsequent corrosion review more specific than “nitric acid caused failure.”
For new equipment, the thermal and mechanical designer should identify where condensation starts, where liquid films can reboil and where cooling conditions are least favourable. The inlet can be especially important: the fluid reported by a bulk process sample may not represent the liquid immediately contacting a hot wall. Alleima’s nitric-acid tubing information specifically identifies local reboiling as a material-selection concern. [1]
DAXUN manufactures stainless-steel and nickel-alloy tubes and performs the agreed processing in-house. We use the process description, drawing and acceptance requirements to define a manufacturable tube order. Each proposed grade, size, treatment and processing scope is confirmed in writing. Zirconium is included below as a comparison route requiring separate supply and construction review.
Establish the service envelope on both sides of the tube
A useful service envelope includes chemistry, temperature, pressure and phase at the vulnerable locations, together with credible excursions. The label “60% nitric acid” is incomplete without the concentration basis, measurement location, operating temperature and contaminants.
Request mass concentration with normal, minimum and maximum values. Distinguish routine operating variation from cleaning, start-up and shutdown exposure. If the available analysis is only a single bulk sample, record that limitation. It should not become evidence that condensate and concentrated surface films always have identical chemistry.
| Input to the material review | Why it changes the decision | Evidence to provide |
|---|---|---|
| Acid concentration and sampling point | Feed, bulk liquid and local film may differ | Process balance and representative analysis with units |
| Bulk and estimated wall temperatures | A hotter wall can alter local evaporation and corrosion | Thermal calculation, operating pressure and fouling assumptions |
| Liquid, vapour and condensate locations | A low liquid-phase rate can miss damage elsewhere | Equipment drawing and exposure map |
| Free/total fluoride, chloride and relevant oxidizing species | Contaminants can change protective-film behaviour | Analysis method, detection limits and credible excursions |
| Cooling-water temperature and composition | The opposite surface may control tube reliability | Water chemistry, treatment and deposit history |
| Welds, bends and tube ends | Fabrication changes the condition and exposed geometry | Joint details, final condition and inspection plan |
Total fluoride and chemically available fluoride should not be treated as automatically equivalent. A primary corrosion study of stainless steels and Alloy 690 in nitric-acid media examined fluoride and phase effects under defined laboratory conditions. Its relevance here is the need to identify actual chemical exposure, not a prescription for chemical treatment or a universal alloy ranking. [4]
Likewise, “more oxidizing” does not guarantee progressively better protection. Research on stainless steel in nitric-acid media distinguishes passive behaviour from conditions associated with rapid dissolution. The study conditions are not a plant operating limit, but they explain why a simple concentration-only compatibility table is insufficient. [5]
Compare candidate routes without declaring a universal winner
Use the material comparison to decide what evidence is needed next, not to select the most expensive name. Qualified stainless steel can remain the correct answer for one location while another requires a different material or construction. The comparison below is a screening framework, not a service guarantee.
| Candidate route | Reason to consider it | Required qualification question |
|---|---|---|
| 304L stainless steel | Established baseline for appropriate nitric-acid conditions | Does the actual wall, phase, contaminant and water-side envelope support it? |
| Controlled nitric-acid-grade high-chromium stainless | A route for more demanding nitric-acid duty and metallurgical control | Which exact grade, impurity limits, final condition and corrosion criteria are being ordered? |
| Alloy 690, UNS N06690 | Documented use in selected nitric-acid and mixed-acid equipment | Is there relevant evidence for this condenser’s tube, weld and exposure conditions? |
| Zirconium candidate, such as Zr 702 | Specialist option where the corrosion and construction case supports it | Have fluoride, chloride-containing vapour, concentrated-acid cracking and joint design been addressed? |
Resolve material, product standard, joining route and inspection together. A solid zirconium tube, a lined construction and a stainless or nickel-alloy tube can require different joint details and acceptance evidence even when they address the same corrosion problem.
Changing tube material can change fabrication and maintenance obligations as well as material cost. Compare alternatives against the same duty and acceptance basis, including the cost of qualification, joining and subsequent inspection. The following are hypothetical screening branches, not DAXUN field cases.
| Observed location or credible exposure | Working concern to investigate | Next evidence and procurement consequence |
|---|---|---|
| Acid-side inlet or first-condensate attack | Local heating and reboiling may make the film more aggressive than the sampled bulk liquid | Map wall temperature and film exposure; compare controlled nitric-acid stainless against the actual delivered tube and joint condition |
| Damage beginning beneath water-side deposits while the acid side remains satisfactory | Cooling-water chemistry or local concentration may control the failure | Investigate deposit chemistry, water conditions and joint geometry before selecting from an acid-resistance chart |
| Fluoride contamination or chloride-containing vapour is credible | Pure-acid or liquid-only evidence may not cover the candidate’s vulnerable exposure | Evaluate the actual contaminant and phase; do not clear zirconium or a 690 substitution solely from a clean-liquid result |
In the first branch, changing only the nominal alloy name leaves the thermal cause poorly defined. A controlled nitric-acid stainless route is relevant because both its chemistry and delivered metallurgical condition can be specified for the duty. The comparison still needs a representative inlet exposure; a general grade label is not enough. [1]
In the second branch, a better acid-side material may provide little benefit if the controlling environment is on the cooling-water side. The review should first establish whether deposits, water treatment or construction are responsible. That finding determines whether to change the tube specification, address the water-side condition, or do both.
The third branch calls for a different evidence package. Ask whether the available trial represented vapour, condensate and the actual contaminant form. If not, the procurement decision remains open until those conditions have been assessed. ATI’s zirconium cautions and the nitric-acid fluoride research demonstrate why that distinction matters. [4][7]
Keep 304L as a baseline, but define its limits
304L should be retained or rejected using the actual service evidence, not dismissed merely because a higher-alloy product is available. Producer application guidance identifies it as a conventional nitric-acid material, while also identifying circumstances that require more resistant grades. Such guidance is a starting point for review, not a universal concentration boundary. [2]
The practical question is whether the proposed 304L condition is adequate at the most demanding location. A unit with acceptable bulk-liquid performance can still experience an inlet or joint problem. Review the hottest metal region, likely local concentration, cooling-water exposure and the condition left by fabrication before approving an unchanged replacement.
Low carbon is useful metallurgical information, but it is not a guarantee against every form of intergranular attack. Published research in nitric-acid media shows that oxidizing conditions can produce severe grain-boundary attack even when the explanation is not simply conventional sensitization. A certificate saying “L grade” therefore does not settle the corrosion assessment. [6]
For a failed tube, request examination that can distinguish general thinning, localized attack, grain-boundary damage and a mechanically initiated defect. The correct scope depends on the evidence available. A grade upgrade aimed at sensitization will not necessarily resolve an opposite-side water problem or an incorrectly made joint.
Where the baseline remains technically suitable, the purchase improvement may be tighter condition control, clearer corrosion acceptance, better traceability or an inspection plan representing the finished tube. That conclusion should emerge from the review; this article does not assume either that 304L is always adequate or that it must always be replaced.
Order nitric-acid-grade stainless by controlled identity
Specify a defined alloy and its additional controls instead of accepting “310,” “310S” or “310L” as a complete description of nitric-acid-grade tubing. Similar commercial names do not prove equal impurity limits, delivered condition or corrosion-test performance.
Alleima’s 2RE10 is a named proprietary example associated with UNS S31002 and EN 1.4335. Its published controls include low carbon, silicon, phosphorus, sulphur and molybdenum, alongside a high-chromium composition. Its producer-specific delivery guarantees belong to that product and test condition; they cannot be transferred to generic 310L material or represented as DAXUN test results. [1]
A purchaser comparing alternatives should ask which chemistry limits are contractual, which tests represent the delivered condition and how the proposed product differs from the reference. If a quotation uses “equivalent,” request the actual comparison rather than accepting the word as a technical conclusion. This should include the product specification and any customer-required supplementary limits.
The final condition matters as much as the starting alloy name. If welding or another operation changes the relevant metallurgical condition, the original tube test may not represent the finished joint. Agree whether supplementary samples must represent that operation and how any subsequent treatment is controlled.
For quotation comparison, place the required grade, impurity limits, final treatment, corrosion-test condition and acceptance criterion on the same schedule. Ask each manufacturer to identify any deviation. This makes an alternative offer technically reviewable before differences in price or delivery are considered.
Evaluate Alloy 690 using the right kind of evidence
Alloy 690 is a candidate when its condition-specific evidence matches the proposed nitric-acid duty. Special Metals identifies nitric-acid tail-gas reheaters and mixed nitric/hydrofluoric-acid heating coils among its applications. A condenser substitution still needs a comparison against qualified nitric-acid-grade stainless under the same relevant exposure. [3]
The mixed-acid example below shows how tightly a useful corrosion number is tied to its test. Special Metals used annealed sheet specimens at 60°C; these conditions differ from a typical cooler-condenser tube qualification. The example is included to explain the evidence check, not to suggest that every nitric-acid plant has an HF duty. [3]
| Material and specimen | Laboratory mixture | Temperature | Reported representative corrosion rate |
|---|---|---|---|
| Alloy 690, annealed sheet | 10% HNO3 + 3% HF | 60°C | 0.15 mm/year |
| Alloy 690, annealed sheet | 15% HNO3 + 3% HF | 60°C | 0.25 mm/year |
These are producer laboratory results, not DAXUN measurements or contract limits. They do not reproduce condenser heat transfer, local films, welded joints or the designer’s remaining-wall criteria. Multiplying the rates by an intended service life would therefore be an unsound way to select tube wall thickness.
For a 690 substitution, identify which supplied tube condition the qualification represents and which service locations it covers. Have the corrosion specialist list the remaining gaps, such as a welded joint or heated condensate exposure, and resolve those gaps before production release.
Do not import a nuclear-material label into this acid-service decision. “690TT” is not a universal requirement for nitric-acid equipment, and nuclear research does not establish the optimum condition for this application. The required treatment must follow the actual product and service specification. For related flat components, the separate 690 sheet and plate guide explains why product-form requirements must remain distinct.
Treat zirconium as a separate qualification route
Zirconium requires specific checks for concentrated-acid stress-corrosion cracking (SCC), fluoride exposure and chloride-containing vapour. ATI’s nitric-acid application bulletin identifies these limitations alongside favourable applications. The candidate should be screened against all three concerns before a general corrosion-resistance claim is accepted. [7]
One ATI laboratory example for boiling 50% nitric acid with 1% sodium chloride reported low liquid-phase rates while also recording vapour-phase pitting. The important selection lesson is that a favourable liquid result does not clear the vapour region; it is not a project acceptance value or a prediction for a particular tube bundle. [7]
Construction must be evaluated separately. A proposed zirconium tube or lined design requires appropriate joint details, inspection and acceptance. Do not assume that a stainless-steel fabrication sequence or an existing tube-to-tubesheet arrangement transfers unchanged. The responsible equipment designer must assess the entire pressure boundary and joining system.
Include credible fuming-acid, drying and excursion conditions in the specialist process and materials review. The resulting requirements must reach the construction specification and qualification plan, so normal operation does not become the only condition assessed.
Inspect the joints and exposed tube ends
Qualify the surfaces and joints that the process will contact, not only the mid-length base tube. Welding, exposed cross sections, local geometry and finishing can create conditions that a flat base-metal specimen does not represent.
Research on end-grain corrosion in boiling nitric-acid environments connects attack at exposed sections with microstructural factors. It supports including tube ends in the evaluation; it does not establish one universal corrective heat treatment for every batch. [8]
In a procurement review, separate the manufactured tube condition from the tube-to-tubesheet joint. Ask which material is exposed at the joint, whether a filler is used, how the procedure is qualified and which final examination is required. If dissimilar materials are involved, their compatibility and construction need a specific design review.
The same approach applies to bends. Identify the final geometry and whether forming changes the condition represented by existing test evidence. A certificate for the original straight tube should not silently become a certificate for every property of the finished component.
For a replacement enquiry, photographs and location drawings can help identify where additional examination is needed. They do not replace sectioning, chemical analysis or other investigations when those are necessary to establish the mechanism. Preserve the distinction between an observed feature, a plausible cause and a confirmed finding.
Separate metallurgical tests from service qualification
Select tests according to the question they answer and define acceptance separately. A named corrosion test is not a general certificate that a tube will survive its intended duty.
| Test or evidence | Appropriate use | Limit that must remain visible |
|---|---|---|
| ASTM A262 Practice C for applicable austenitic stainless steel | Assess specified intergranular-corrosion susceptibility | Does not establish general, pitting or stress-corrosion resistance in all services |
| ASTM G31-based immersion programme | Organize documented laboratory mass-loss testing | Does not by itself cover localized attack, cracking or solution-flow effects |
| Proposed corrosion testing of Alloy 690 | Address a defined uncertainty using an agreed valid procedure | G28-24 Method A’s published alloy list does not include N06690 |
| Representative weld/end/phase evaluation | Examine the condition and location that may control failure | Must state the specimen, exposure, examination and acceptance basis |
ASTM A262-15(2021) applies to specified austenitic-stainless corrosion practices. Its own scope cautions against broad service-performance conclusions. A Huey result therefore needs the tested condition and agreed limit, and it should not be applied automatically to Alloy 690 or zirconium. [9]
ASTM G31-21(2025) is a guide for laboratory immersion corrosion testing. It identifies variables that must be recorded, but its scope excludes specific evaluation of localized corrosion, environment-assisted cracking and solution-flow effects. Additional work is needed when those mechanisms control the actual equipment problem. [10]
For 690, do not select ASTM G28 merely from its title. N06690 is absent from the publicly listed Method A materials in G28-24. The responsible specialist and purchaser must establish a valid procedure and acceptance basis instead of requiring an unsupported routine “G28 pass.” [11]
Design the qualification request around the unresolved risk
A useful test request explains what decision the result will support. It should identify the candidate product, final condition and exposure, and state what evidence would justify acceptance or rejection. Testing several alloys in unmatched conditions cannot establish a defensible ranking.
For a condenser uncertainty, the agreed programme may need separate liquid, vapour and condensate exposures, plus a justified way to represent a heated wall. Distinguish base metal from representative joints. The corrosion specialist should define specimen preparation, monitoring, duration and examination around the suspected mechanism.
Record chemistry before and during exposure where changes could affect interpretation. After testing, report the method used to evaluate mass loss and any required localized attack, section condition or cracking assessment. If a mechanism was not examined, say so. A single favourable average rate should not obscure a small region of severe penetration.
The acceptance plan should then connect the qualification evidence to production. Identify which material and treatment variables must remain controlled, which routine tests are required and what change would trigger renewed approval. Otherwise a well-executed trial can become disconnected from the tubes later delivered.
Use tube standards without confusing them with design approval
Specify the correct product form and grade, then add the service-specific requirements. A tube specification addresses supplied material; it does not complete the exchanger’s pressure design, corrosion assessment or customer approval.
Relevant standard families include ASTM A213/A213M-25 for seamless steel exchanger tubing and A249/A249M-24ae1 for welded austenitic tubing. For a specific nitric-acid grade, verify its exact inclusion and supplementary requirements in the controlled edition. A generic pipe specification should not be substituted just because a quotation calls the product “tube/pipe.” [12][13]
ASTM B163-26a is the seamless nickel-alloy condenser and heat-exchanger tube route relevant to a proposed 690 order, with the actual alloy/condition and dimensional requirements checked against the contract. ASTM B523/B523M-18(2023) addresses zirconium-alloy tubes; flat-product or pipe standards are different purchase objects. [14][15]
Do not turn this list into a promise that every listed grade, condition or size is available from DAXUN. The quotation should confirm the accepted product route, dimensions, condition and any deviations. The designer remains responsible for applicable code requirements and allowable stresses.
Send the exchanger location, both-side chemistry, wall-temperature estimate, excursions, tube drawing, material condition and inspection requirements for technical RFQ review.
Convert the selected route into a traceable DAXUN order
The final order should connect the approved material decision to in-house manufacture, processing and inspection. DAXUN manufactures the agreed stainless or nickel-alloy tubing and performs the confirmed processing in-house; independent inspection can supplement that work without replacing the manufacturing responsibility.
Define a material record that follows the heat through manufacturing, treatment, inspection and final packing. If cutting, bending or end preparation is included, identify the delivered geometry and the verification after processing. For corrosion-sensitive equipment, the buyer should also specify the required surface condition, cleaning acceptance and protection during transport.
The DAXUN testing page and heat-treatment information provide starting points for discussing the production package. Exact methods, acceptance limits, witness arrangements and any external laboratory approval must be agreed for the order; a service-page description does not establish an accreditation or a particular project’s approval.
Send the following with a technical RFQ to DAXUN: the exchanger duty and location, both-side chemistry, normal and limiting temperatures and pressures, wall-temperature estimate, contaminant analysis, proposed material and condition, tube drawing, dimensions and wall basis, quantity, joint details, inspection requirements and destination. For a retube project, add the previous certificate and available failure findings.
Where the material is not yet approved, separate the qualification enquiry from the production release. This allows the response to identify what can be manufactured and what still requires engineering acceptance, without turning an early quotation into an unintended service guarantee.
Frequently asked questions
What is the best tube material for a nitric-acid cooler-condenser?
There is no universal winner. Start with the wall temperature, acid concentration, phase, contaminants, fabrication and water-side conditions. Compare 304L, an identified nitric-acid-grade stainless and any justified alternative using matched evidence and a defined acceptance plan.
Does nitric-acid concentration alone decide whether 304L is suitable?
No. Concentration matters, but a hot inlet film, reboiling, impurities or an opposite-side problem can control performance. A bulk sample and a nominal alloy designation do not establish the conditions at every part of the tube. [1][2]
Can ordinary 310S substitute for nitric-acid-grade 310L or S31002?
Not automatically. The exact chemistry controls, final condition, product specification and corrosion requirements must be compared. A named proprietary nitric-acid product’s guarantee cannot be assumed for a generic commercial grade or transferred to another manufacturer’s material. [1]
Is Alloy 690 always a better choice than nitric-acid-grade stainless steel?
No. Its documented applications make it a credible candidate, but the available laboratory and application examples do not establish superiority under every condenser condition. Qualify the actual tube and joints against the relevant exposure instead of ranking alloys by nickel content. [3]
Does passing a Huey test prove the expected exchanger life?
No. ASTM A262 testing addresses defined metallurgical susceptibility in applicable stainless steels. It does not certify lifetime resistance to every local environment, pitting or stress-corrosion mechanism. Service suitability and routine material acceptance are related but separate decisions. [9]
Why are fluoride and chloride results requested with the RFQ?
They can alter corrosion behaviour and the suitability of a candidate. Their effects depend on material, chemical form and exposure location; zirconium’s nitric-acid literature specifically warns about fluoride and chloride-containing vapour. Provide measured values and analytical context rather than assuming a universal safe limit. [4][7]
What should accompany a failed-tube replacement request?
Include the tube map, damage location, prior material certificate, operating and cleaning history, both-side chemistry, dimensions and any examination results. State what is confirmed and what is still suspected. Those distinctions help avoid ordering an expensive replacement that leaves the controlling problem unchanged.
Technical Accuracy Statement
This article provides a conditional procurement framework, not a process operating procedure or a guaranteed corrosion envelope. Producer laboratory results remain tied to their specimen, temperature and medium. Public standard scopes were checked; full controlled editions and project requirements govern acceptance. The screening branches are illustrative, not plant trials. Material and equipment approval remain with the responsible project specialists.
Last reviewed date: September 23, 2026.
Technical Sources
- Alleima — 2RE10 seamless tube and pipe datasheet, updated May 9, 2025; nitric-acid duty, identity and producer-specific controls.
- Alleima — Nitric acid plant and equipment manufacturers; application screening guidance.
- Special Metals — INCONEL alloy 690, SMC-079, October 2009; applications and annealed-sheet mixed-acid test data.
- AMPP, CORROSION 68(2), 026002, 2012 — Corrosion Behavior of Type 304L Stainless Steels in Nitric Acid Containing Free and Complexed Fluoride; publisher abstract.
- Corrosion Science 107, 182–192, 2016 — Kinetics of the oxidation of stainless steel in hot and concentrated nitric acid in the passive and transpassive domains; publisher abstract.
- Corrosion Science, 2011 — Corrosion behaviour of AISI type 304L stainless steel in nitric acid media containing oxidizing species; publisher abstract.
- ATI — Zircadyne nitric-acid application bulletin, version 1, February 24, 2014; typical data and limitations.
- Materials Science Forum 702–703, 693–696, 2012 — End Grain Corrosion: Establishing Microstructural Causes and Preventive Steps; publisher abstract.
- ASTM A262-15(2021) — Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels.
- ASTM G31-21(2025) — Laboratory Immersion Corrosion Testing of Metals.
- ASTM G28-24 — Intergranular Corrosion in Wrought, Nickel-Rich, Chromium-Bearing Alloys; Method A scope.
- ASTM A213/A213M-25 — Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes.
- ASTM A249/A249M — Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser Tubes; official listing identifies active 24ae1 revision.
- ASTM B163-26a — Seamless Nickel and Nickel Alloy Condenser and Heat-Exchanger Tubes.
- ASTM B523/B523M-18(2023) — Seamless and Welded Zirconium and Zirconium Alloy Tubes.
