Design Acceptance Criteria (DAC) vs Manufacturing Acceptance Criteria (MAC)

Understanding the Difference Between Design Acceptance Criteria (DAC) and Manufacturing Acceptance Criteria (MAC) is essential in implementing API Q1 requirements.

In the world of upstream oil and gas, particularly for pressure-containing and pressure-controlling equipment under API 6A, the terms Design Acceptance Criteria (DAC) and Manufacturing Acceptance Criteria (MAC) are foundational to ensuring product integrity. These two criteria play distinct yet interconnected roles throughout the product lifecycle—from concept and design to machining, welding, assembly, and final product validation.

AspectDACMAC
PurposeTo ensure that a product performs its intended function safely and reliablyTo ensure that the product has been manufactured correctly and consistently
FocusProduct performance, functionality, and compliance with design intentQuality of manufacturing processes and workmanship
Primary Input FromDesign engineers, customers, API 6A, ASME codes, and finite element analysisManufacturing floor team, QA/QC, work instructions, and internal procedures

Definition of Design Acceptance Criteria:

Requirements applied to characteristics (or combinations of those characteristics) of materials, products, or components to achieve conformity to the specified design requirements and/or required design performance.

DAC is the performance expectation of the product at the design level. It defines the minimum technical, functional, and safety criteria that a valve or its components must meet in design calculations, drawings, and simulations.

Eamples:

  • A ball valve rated for 10,000 psi must be designed to withstand:
    • Burst pressure of 1.5x rated pressure without rupture (per API 6A Annex F).
    • Full open/close operation after 200 cycles at max pressure and temperature.
  • Material selection for bodies and trims must meet the minimum yield strength and corrosion resistance for H2S service (per NACE MR0175 if sour service).
  • Sealing mechanism must ensure zero leakage at rated pressure (as per PSL 3+ requirements).

Think of DAC as the “design promise” — what the valve must do according to engineering and functional expectations.

Manufacturing Acceptance Criteria:

Definition:

Requirements applied to characteristics (or combinations of those characteristics) of materials, products, or components to achieve conformity to DAC and other product manufacturing requirements.

MAC is the practical, shop-floor verification that ensures the manufactured product matches the design intent (DAC) and complies with applicable manufacturing controls.

Example:

  • Hardness testing on valve stem: Must be between 28–32 HRC to conform with DAC material strength requirements.
  • Hydrostatic shell test: Must demonstrate no leakage at 1.5x rated pressure to verify structural integrity.
  • Welding procedure qualification and welder qualifications: Must conform to ASME IX and API 6A requirements for joint strength and impact toughness.
  • NDE (MPI/UT) acceptance criteria: Must follow severity levels per ASTM E709 or API 6A Annex L to confirm no cracks or critical flaws.

Think of MAC as the “workshop real” — verifying through inspection, testing, and measurement that the product truly performs as designed.

DAC sets the functional targets, while MAC provides the way of achieving and checkpoints to reach them.

  • If DAC is not met → Product cannot perform its intended function → Not acceptable unless DAC is revised (with customer and regulatory approval).
  • If MAC is not met but DAC is met → Organization may evaluate release under concession, provided:
    • MAC deviation does not compromise the DAC.
    • Client approval and change control (e.g., MOC process) are in place.
    • Records justify the decision (refer to API Q1 5.9.3 and 5.9.4).
  • When MAC Fails but DAC Holds:
    • Concession under API Q1 is permitted only when:
    • The product still satisfies all DAC and/or customer specifications.
    • The violated MAC characteristics are not critical to DAC (e.g., cosmetic scratches).
    • DAC is formally revised through a documented MOC and approved by the customer.
  • 🛑 Important: No MAC nonconformity should be released unless it is rigorously evaluated for impact on product integrity, and proper risk-based disposition is recorded.