Codes, standards & testing
The rules we design and build to
A code is not paperwork. It is the accumulated record of how equipment has failed in the past and what stops it happening again. Here is what each of the ones we work to actually governs, and what we do to prove compliance.
Design codes
Which code governs what
| Code / standard | Governs | Applies to |
|---|---|---|
| ASME BPVC Section VIII Div. 1 | Pressure vessel design, materials, fabrication, examination and testing | All pressure vessels; the pressure parts of exchangers and reactors |
| ASME BPVC Section II | Material specifications and allowable stresses | Plate, pipe, tube, forgings, bolting, welding consumables |
| ASME BPVC Section V | Non-destructive examination methods | All NDT performed on code work |
| ASME BPVC Section IX | Welding and brazing procedure and performance qualification | WPS, PQR and welder qualification records |
| TEMA | Shell and tube exchanger mechanical standards and nomenclature | All shell & tube exchangers |
| API 660 | Shell and tube exchangers for petroleum and chemical service | Refinery and petrochemical exchangers |
| API 661 | Air-cooled heat exchangers for petroleum service | Fin-fan / ACHX units |
| API 650 | Welded atmospheric storage tanks | Vertical, flat-bottom, above-ground tanks |
| API 620 | Low-pressure storage tanks, to about 1 barg | Low-pressure and refrigerated storage |
| API 653 | Tank inspection, repair, alteration and reconstruction | Assessment and repair of existing tanks |
| EN 13445 | European unfired pressure vessel design | Projects following the PED route |
| ASME B31.1 / B31.3 | Power piping and process piping | Pipe spools, skid pipework, interconnecting piping |
| ASME B16.5 / B16.47 | Pipe flanges and flanged fittings | Nozzle and connection flange ratings |
| AWS D1.1 | Structural steel welding | Skid frames, supports, platforms, structures |
| NACE MR0175 / ISO 15156 | Materials for sour service | Equipment in H₂S-bearing service |
TEMA classes
R, C or B — and why it changes the price
The class sets minimum thicknesses, corrosion allowances and construction tolerances. Ask for R when you do not need it and you pay for metal you will never use.
Class R
Severe service. Petroleum and related processing. The most demanding requirements: larger corrosion allowance, heavier minimum thicknesses, tighter tolerances. Specify it for refinery and petrochemical duty.
Class C
Moderate service. General commercial and process duty. Economical construction for clean, non-severe applications. The right choice for most utility and industrial exchangers.
Class B
Chemical service. Similar economy to C but with provisions suited to chemical process duty. Common where the fluid is aggressive but the service is not hydrocarbon-severe.
If you do not specify a class, we will propose one with our reasoning and you can confirm it. See also our guide to reading TEMA designations.
Welding
Qualified procedures, qualified welders
Under ASME IX nothing is welded on a code job without a qualified procedure and a welder qualified to it. Both records go into your dossier.
WPS
Welding Procedure Specification — the written instruction for a specific joint, material and position.
PQR
Procedure Qualification Record — the destructive test evidence proving the WPS produces a sound weld.
WQR
Welder Qualification Record — proof that the individual welder can execute that procedure.
Weld map
A drawing identifying every weld, the procedure used, the welder, and the NDT applied to it.
Processes
SMAW, GTAW (TIG), GMAW (MIG), FCAW and SAW, selected by joint type, material and thickness.
Joint preparation
Machined or ground bevels, controlled root gaps, backing where full penetration cannot be achieved from both sides.
Post-weld heat treatment
Stress relief where thickness, material or service requires it, with a recorded time-temperature chart.
Non-destructive examination
Five methods, each finding a different kind of flaw
The inspection and test plan states which method applies to which weld, and at what coverage.
| Method | Detects | Typical use |
|---|---|---|
| Visual (VT) | Surface profile, undercut, overlap, misalignment, arc strikes | Every weld, at every stage |
| Radiography (RT) | Internal volumetric flaws — porosity, slag, lack of fusion | Butt welds in shells and heads; spot or full coverage per code |
| Ultrasonic (UT) | Internal planar flaws and laminations; also wall thickness | Thick sections, and where radiography is impractical |
| Magnetic particle (MT) | Surface and near-surface cracks in ferromagnetic materials | Nozzle welds, attachment welds, after PWHT |
| Dye penetrant (PT) | Surface-breaking flaws in any non-porous material | Stainless and non-ferrous welds, tube-to-tubesheet joints |
Coverage is not a fixed number. It depends on joint category, material, thickness and the joint efficiency assumed in the design calculation — specifying full radiography lets us use a higher joint efficiency and therefore a thinner shell.
Pressure testing
Proving the pressure envelope
Hydrostatic test
The default. Water at a code-defined multiple of design pressure, held and inspected. Safe because water is nearly incompressible — a failure releases very little stored energy.
Water chemistry is controlled for stainless and duplex work: chloride content is limited and the equipment is drained and dried afterwards to avoid pitting.
Pneumatic test
Used only where water is unacceptable — equipment that cannot be dried, cannot carry the water weight, or is in a service where residual moisture is a problem.
Compressed gas stores far more energy than water, so a pneumatic test runs under a written procedure with exclusion zones and staged pressurisation.
Tube-side / shell-side sequence
Exchangers are tested side by side so a tube-to-tubesheet leak is found and located rather than masked by equal pressure either side of the joint.
Leak testing
Where a hydrotest is not sensitive enough: soap bubble, pressure decay, or helium mass spectrometry for genuinely leak-tight service.
Documentation
The dossier you receive
Assembled as the job progresses, not reconstructed at the end.
Design calculations
Thickness, reinforcement, flange rating, supports, MAWP.
As-built drawings
GA, nozzle orientation and schedule, weld details, internals.
Material certificates
Mill certificates for every pressure-retaining component.
Heat number map
Which certificate applies to which physical part.
Welding records
WPS, PQR, welder qualifications, weld map.
NDT reports
Reports with film, scan data or images as applicable.
PWHT chart
Time-temperature record where heat treatment applied.
Test certificate
Pressure test record and nameplate details.
Being straight with you
Designed to code, and code stamped, are not the same thing
This distinction causes more confusion in tender documents than any other, so it is worth being explicit.
Designed and built to ASME VIII Div. 1 means every calculation, material choice, weld procedure, examination and test follows the rules of the code, and you receive the evidence. This is what the great majority of industrial projects require.
A certified ASME U-Stamp is an additional formal step. It requires the manufacturer to hold a current ASME Certificate of Authorization, operate an audited quality system, and have the work witnessed and signed off by an Authorised Inspector from an accredited agency, who then countersigns the Manufacturer's Data Report.
The same distinction applies to CE marking under the PED, and to third-party certification by bodies such as TÜV, Lloyd's Register or Bureau Veritas: all can be arranged as part of the project scope, and all need to be agreed before fabrication starts.
Have a specification to review?
Send it over. We will confirm which codes apply and what the inspection route looks like.