Sheet metal and welded parts for data center cooling are the fabricated hardware of the coolant and air circuits: manifolds and headers, frames for coolant distribution units, enclosures and casings. For the parts that carry coolant, a supplier qualifies through a qualified weld procedure, qualified welders, a fabricator working to a level of ISO 3834, and a leak test with a named method and a written acceptance criterion.
Which sheet metal and welded parts does a data center cooling system use?
A liquid-cooled hall has a coolant side and an air side. On the coolant side the parts are manifolds and headers that distribute the liquid to racks, and the frames or skids that carry the pumps and heat exchangers of a coolant distribution unit. Their requirement is a joint that does not leak. On the air side the parts are rack and aisle enclosures, doors, panels, drip trays and air-handler casings. Their requirement is dimension, fit and finish. Table 1 sorts them by process and by what a purchase order can call for; Table 3 explains the leak test methods.
Table 1. Part types for data center cooling, process route and requirements to call for
| Part type | Process route | Weld and quality requirements | Test | Documents |
|---|---|---|---|---|
| Coolant manifolds and headers | Cutting of tube and sheet, fit-up, arc welding, weld cleaning | ISO 15614-1 or -2 procedure; ISO 9606-1 or -2 welders; ISO 5817 or ISO 10042 level on the drawing | Leak test of every part, method per Table 3; visual test to ISO 17637 | Material certificate, welding records, leak test record |
| Frames and skids for coolant distribution units | Cutting, welding, machining of mounting faces | ISO 3834 level agreed; ISO 5817 level; ISO 13920 | Visual test to ISO 17637; leak test of integrated pipework | Material certificate, weld records, dimensional report |
| Rack and aisle enclosures, doors, panels | Laser cutting, bending, spot or arc welding | ISO 2768-1 class on the drawing | Dimensional check | Certificate of conformity, dimensional report |
| Casings, ducts, drip trays | Sheet metal, welded or sealed seams | Level for seams that hold liquid | Water or bubble test of those seams | Certificate of conformity, test record |
Source: ISO 5817:2023; ISO 10042:2018; ISO 13920:2023; ISO 2768-1:1989; ISO 17637:2016. The grouping of parts, tests and documents is our recommendation, not a requirement of these standards.
Our network in Bursa covers sheet metal and welded assemblies; the page on data center cooling and power equipment lists the part families. Which weld records and test methods are available for a specific part is confirmed at quotation, from the drawing.
Which weld qualification does a coolant-carrying part need?
A welded coolant part carries four separate qualifications: the procedure, the welder, the fabricator's quality system and the acceptance level of the finished weld. The standard for each depends on the material.
Table 2. Weld qualification chain by material, status as of 2026-10-30
| Element | Steel, including stainless | Aluminium |
|---|---|---|
| Welding procedure test | ISO 15614-1:2017 with Amd 1:2019 | ISO 15614-2:2025 |
| Welder qualification | ISO 9606-1:2012 (European adoption EN ISO 9606-1:2017) | ISO 9606-2:2004 |
| Imperfection levels B, C, D | ISO 5817:2023 | ISO 10042:2018 |
| Fabricator quality level | ISO 3834-2, -3 or -4, chosen by ISO 3834-1 | ISO 3834-2, -3 or -4, chosen by ISO 3834-1 |
Source: ISO catalogue entries listed under Sources, checked 2026-10-30.
Three status points matter on a drawing or an order:
- ISO 15614-2 is new. The 2025 edition replaced the 2005 edition, which is withdrawn. For steel, ISO 15614-1:2017 is current and a third edition reached the approval stage on 2026-10-21. Per the ISO page, qualifications under earlier editions remain usable where the current edition is specified.
- ISO 9606 is under revision. Parts 1 and 2 are flagged "to be revised", and a draft ISO 9606 that would replace parts 1 to 5 closed its ballot on 2026-07-28. Until it is published, the existing parts apply.
- ISO 5817 does not cover aluminium. It applies to steel, nickel, titanium and their alloys from 0.5 mm thickness. Aluminium joints are judged to ISO 10042, with levels B, C and D from above 0.5 mm. Level B is the strictest in both, and both describe production quality, not fitness for purpose.
ISO 15614-1 defines two test levels. Level 2 means more testing and narrower qualification ranges, and it applies when the contract names no level.
ISO 3834-2:2021 (comprehensive) was confirmed on 2026-09-22. ISO 3834-1:2021 gives the criteria for choosing between parts 2, 3 and 4 and has been under systematic review since 2026-07-15. The level is the buyer's choice. In our view, for a coolant circuit above live IT equipment the consequence of a leak, not the pressure alone, argues for the higher level.
Weld NDT personnel are certified to ISO 9712:2021, which replaced the 2012 edition. Visual testing of fusion-welded joints follows ISO 17637:2016, confirmed in 2022.
Does the Pressure Equipment Directive apply to cooling loops?
For most coolant circuits in a data hall, no, and that moves the assurance from the law to the order. Directive 2014/68/EU (PED) sets its limits in Article 4. For liquids whose vapour pressure at the maximum allowable temperature does not exceed atmospheric pressure by more than 0.5 bar, group 2 piping falls under the directive only above PS 10 bar, above DN 200 and above a PS×DN product of 5000 bar. For vessels the corresponding group 2 limit is PS above 10 bar and PS×V above 10 000 bar·L, or PS above 1000 bar.
A manifold designed for PS 6 bar at DN 50 is below all of these limits. Our reading is that this covers a water-based coolant loop at normal operating temperature. Equipment below the limits follows the sound engineering practice of a Member State and must not bear the CE marking (Article 4(3)).
Above the limits, Annex I section 3.1.2 requires qualified personnel and defined procedures for permanent joints. For categories II, III and IV a competent third party approves procedures and personnel, and for categories III and IV the NDT personnel need approval by a third-party organisation recognised by a Member State (section 3.1.3). Below the limits none of this is mandatory, so a buyer who wants the same assurance has to require the ISO 15614 and ISO 9606 records in the order.
EN 1090 is a separate question. It applies to load-bearing steel or aluminium components permanently installed in buildings or civil engineering works and placed on the market (TÜV Austria summary). Support steelwork for a roof-mounted cooler platform can fall under it; a coolant manifold or a unit skid does not.
Which leak test method fits which part?
The choice depends on whether the part can be pressurised or evacuated, how small the allowable leak is and whether the leak has to be located or only detected.
Table 3. Leak test methods for welded and sheet metal parts
| Method | Standard | What it does | Where it fits |
|---|---|---|---|
| Bubble emission | EN 1593:1999 | Detects and locates leaks by immersion or liquid application on equipment that can be evacuated or pressurised | Welded seams, panels and trays where a leak must be found and repaired |
| Pressure change | EN 13184:2001 | Measures the leakage rate of an isolated object under a pressure difference from the change of pressure, or pressure and temperature, inside it | Closed manifolds and loops tested as a whole |
| Tracer gas | ISO 20485:2017 | Detects leaks with a tracer gas and a leak detector specific to that gas | Manifolds and assemblies with a stated maximum leak rate |
| Hydrostatic or pneumatic strength test | Order specification | Proves the part holds the test pressure | Parts with a stated design pressure |
Source: EN 1593:1999 (review closed 2025-06-04) and EN 13184:2001 (confirmed 2024-09-24), status per Genorma; ISO 20485:2017 (ISO catalogue, review closed 2023). The strength test pressure comes from the specification.
EN 1593 notes that bubble emission sensitivity depends on the techniques and materials used, so a bubble test does not give a leak rate; pressure change or tracer gas does. The standards describe the techniques, and the acceptance criterion comes from the buyer's specification. The drawing or order therefore has to give the method, the test medium, the test pressure, the hold time or the maximum allowable leak rate, and who signs the record.
Test after welding and before any coating, and again after any repair weld. A part reworked after its test carries a record that no longer describes it.
Which tolerances apply to welded sheet metal and frames?
Two tolerance standards split the part. ISO 2768-1:1989 covers workpieces formed from sheet metal, which includes laser-cut and bent panels; it is published and flagged for replacement by a single ISO 2768. ISO 13920:2023 covers lengths, angles, shape and position of welded constructions in four classes chosen by function. It states that a drawing without individual tolerances or a reference to the general tolerances is incomplete.
A welded frame distorts with heat input, so mounting faces for pumps, heat exchangers and flanges are machined after welding, and the drawing should say so. The article on welded assemblies, weld quality levels and ISO 3834 shows how levels and tolerance classes combine on one drawing.
What should the drawing and the purchase order state?
Anything the drawing leaves open, the supplier decides at quotation. Check these before it goes out:
- Material and certificate. Grade and the inspection document type, for example an EN 10204 type 3.1 certificate for the material of the delivered batch. See EN 10204 inspection certificates for what each type proves.
- Weld standards with editions. Procedure test (ISO 15614-1 or -2, level 1 or 2), welder qualification (ISO 9606-1 or -2) and quality level (ISO 5817 or ISO 10042), each with its year.
- ISO 3834 part. 2, 3 or 4.
- Tolerances. ISO 13920 class for as-welded dimensions, ISO 2768-1 class for sheet metal, individual tolerances for machined faces.
- Leak test. Method, medium, pressure, hold time or maximum leak rate, and the point in the process where it is done.
- Weld surface and cleanliness. Heat tint, weld cleaning and flushing requirements come from the circuit design and belong on the drawing.
- Records. Welding records, leak test record and material certificates, shipped with the part under its part number and revision.
Road freight from Bursa to central Europe typically takes 5 to 10 days, so a part that fails at incoming inspection costs another transport cycle. Agree the test before the order.
Frequently asked questions
- Which weld qualification does a data center coolant manifold need?
- A welding procedure qualified to ISO 15614-1 for steel or ISO 15614-2 for aluminium, welders qualified to ISO 9606-1 or ISO 9606-2, and a fabricator working to a level of ISO 3834. Imperfection limits come from ISO 5817 (steel) or ISO 10042 (aluminium), with the quality level stated on the drawing.
- Does the Pressure Equipment Directive apply to data center coolant piping?
- Usually not. For group 2 liquids whose vapour pressure stays within 0.5 bar of atmospheric pressure, Directive 2014/68/EU covers piping only above PS 10 bar, above DN 200 and above PS×DN 5000 bar. Below those limits the piping follows sound engineering practice and carries no CE marking, so weld qualification and testing must be written into the order.
- Which leak test is used on welded coolant manifolds?
- The method is chosen per part and written into the order: bubble emission (EN 1593), pressure change (EN 13184) or tracer gas (ISO 20485). The standards describe the techniques. The test pressure, hold time or maximum leak rate has to come from the specification.
- Is ISO 9606-1 still valid for welder qualification?
- Yes. ISO 9606-1:2012 is the current edition (adopted in Europe as EN ISO 9606-1:2017) and is flagged for revision. A draft ISO 9606 that merges parts 1 to 5 completed its ballot on 2026-07-28 and is not yet published.
- Is EN 1090 required for cooling skids and frames?
- Only if the item is a load-bearing steel or aluminium component permanently installed in a building or civil engineering structure and placed on the market as such. Equipment frames and coolant manifolds are normally governed by the order and ISO 3834 instead. The buyer states which applies.
Sources
- ISO 3834-1:2021, criteria for the selection of the quality level, under systematic review since 2026-07-15 (ISO catalogue)
- ISO 3834-2:2021, comprehensive quality requirements, confirmed 2026-09-22 (ISO catalogue)
- ISO 15614-1:2017, welding procedure test for steels and nickel alloys, confirmed 2022 (ISO catalogue)
- ISO/FDIS 15614-1, third edition in approval stage 2026-10-21 (ISO catalogue)
- ISO 15614-2:2025, welding procedure test for aluminium, replaces the 2005 edition (ISO catalogue)
- ISO 9606-1:2012, qualification testing of welders, steels (ISO catalogue)
- SS-EN ISO 9606-1:2017, European adoption of ISO 9606-1:2012 (SIS, Swedish Standards Institute)
- ISO 9606-2:2004, qualification testing of welders, aluminium (ISO catalogue)
- ISO/DIS 9606, merged welder qualification standard, close of voting 2026-07-28 (ISO catalogue)
- ISO 5817:2023, quality levels for imperfections in fusion-welded joints in steel, nickel, titanium (ISO catalogue)
- ISO 10042:2018, quality levels for imperfections in arc-welded aluminium joints (ISO catalogue)
- ISO 13920:2023, general tolerances for welded constructions (ISO catalogue)
- ISO 2768-1:1989, general tolerances for linear and angular dimensions (ISO catalogue)
- ISO 17637:2016, visual testing of fusion-welded joints (ISO catalogue)
- ISO 9712:2021, qualification and certification of NDT personnel (ISO catalogue)
- ISO 20485:2017, leak testing, tracer gas method (ISO catalogue)
- EN 1593:1999, leak testing, bubble emission techniques (Genorma, CEN/TC 138)
- EN 13184:2001, leak testing, pressure change method (Genorma, CEN/TC 138)
- Directive 2014/68/EU, Article 4, text as adopted (legislation.gov.uk, reproduction of the Official Journal text)
- Directive 2014/68/EU, Annex I sections 3.1.2 and 3.1.3, text as adopted (legislation.gov.uk)
- EN 1090-1, components covered and execution classes (TÜV Austria, certification body)
- EN 10204:2004, types of inspection documents (Irish standards shop, status current)
Questions on a drawing? sales@ertas.engineering