Inspection & Testing (ET105) cheat sheet

Inspection is the process of measuring, examining, testing, or gauging one or more characteristics of a product and comparing the results with specified requirements.

Accuracy is the closeness of agreement between a measured value and the true value; precision is the closeness of agreement among repeated measurements.

A defect is a nonconformity that is severe enough to render a product unfit for its intended use; a nonconformity is any departure from a specification.

The quality control loop consists of plan, do, check, act (PDCA); inspection is the 'check' step.

First article inspection (FAI) verifies that the manufacturing process can produce parts that meet all drawing and specification requirements before full production.

Inspection by attributes classifies units as conforming or nonconforming; inspection by variables measures a quantitative characteristic.

A sampling plan defines the sample size and the acceptance number; a lot is accepted if the number of nonconforming units is less than or equal to the acceptance number.

The 'five M's' affecting quality are man, machine, material, method, and measurement (sometimes 'milieu' is added as a sixth).

Traceability is the ability to trace the history, application, or location of an item by means of recorded identification.

A code is a set of rules adopted by a jurisdiction and having the force of law; a standard is a consensus document that may be referenced by a code.

ISO 9001 specifies requirements for a quality management system; ISO/IEC 17025 specifies competence for testing and calibration laboratories.

ASME Boiler and Pressure Vessel Code, Section VIII, governs pressure vessels; Section IX covers welding qualifications.

The ASME B31 series covers pressure piping; B31.3 is the process piping code.

AWS D1.1 is the structural welding code for steel; it defines acceptance criteria for visual and NDT examination of welds.

ASTM standards are voluntary consensus standards; many are referenced by codes and become mandatory when invoked in a contract or regulation.

Regulatory bodies (e.g., OSHA, FDA, NRC) issue rules that may incorporate standards by reference, giving them legal effect.

The hierarchy of requirements is typically: contract > code > standard > company procedure > work instruction.

Visual inspection is the primary method for detecting surface discontinuities, corrosion, misalignment, and workmanship defects; it requires adequate illumination (typically 100–200 foot-candles for general inspection).

Direct visual inspection is performed with the unaided eye; remote visual inspection uses borescopes, fiberscopes, or cameras.

Dimensional inspection compares part dimensions to drawing tolerances using calipers, micrometers, height gauges, or CMMs.

GD&T (geometric dimensioning and tolerancing) controls form, orientation, location, and profile; symbols are defined in ASME Y14.5.

A micrometer measures outside dimensions; a caliper measures outside, inside, and depth; a height gauge measures vertical distance from a surface plate.

Surface roughness is quantified by Ra (arithmetic average) or Rz (average peak-to-valley); values are typically in micrometers or microinches.

Weld visual inspection checks bead contour, undercut, overlap, spatter, and craters; acceptance limits are in the applicable welding code.

Dimensional inspection should be performed at a temperature near 20 °C (68 °F) to avoid thermal expansion errors.

Liquid penetrant testing (PT) detects surface-breaking discontinuities in nonporous materials; it uses a penetrant, developer, and either visible or fluorescent dye.

Magnetic particle testing (MT) detects surface and near-surface discontinuities in ferromagnetic materials; it uses magnetic fields and iron particles.

Ultrasonic testing (UT) uses high-frequency sound waves to detect internal discontinuities and measure thickness; it requires a couplant.

Radiographic testing (RT) uses X-rays or gamma rays to produce an image of internal structure; it detects volumetric discontinuities.

Eddy current testing (ET) detects surface and near-surface discontinuities in electrically conductive materials; it is used for tubing inspection.

Acoustic emission testing (AE) monitors stress waves released by active defects under load; it is a passive method.

Visual testing (VT) is the most common NDT method and is often required before other NDT methods.

Each NDT method has limitations: PT and MT detect surface defects; UT and RT detect internal defects; ET detects surface and near-surface defects in conductive materials.

Tensile testing measures yield strength, ultimate tensile strength, elongation, and reduction of area.

Hardness testing (Brinell, Rockwell, Vickers) measures resistance to indentation; results are empirical and scale-specific.

Impact testing (Charpy or Izod) measures energy absorbed during fracture; it is used to evaluate toughness and ductile-to-brittle transition.

Bend testing evaluates ductility and soundness of welds; the specimen is bent to a specified angle and examined for cracks.

Macroetch and microetch examinations reveal weld penetration, heat-affected zone, and microstructure.

Fatigue testing applies cyclic stresses to determine the number of cycles to failure at a given stress amplitude.

Corrosion testing may include salt spray (ASTM B117), immersion, or electrochemical methods.

Destructive testing is performed on coupons or samples that are representative of the production lot; results do not directly verify the tested part's fitness for service.

Calibration is the comparison of a measurement instrument's output to a reference standard of known accuracy.

Traceability requires an unbroken chain of calibrations to national or international standards.

Measurement uncertainty is the parameter that characterizes the dispersion of values that could reasonably be attributed to the measurand.

Type A uncertainty is evaluated by statistical methods; Type B uncertainty is evaluated by other means (e.g., manufacturer specifications, calibration certificates).

Combined standard uncertainty is the root-sum-square of the individual standard uncertainties; expanded uncertainty is the combined standard uncertainty multiplied by a coverage factor (k, typically 2 for 95% confidence).

Calibration intervals should be established based on instrument stability, usage, and manufacturer recommendations.

A calibration certificate should include the reference standard used, environmental conditions, results, and uncertainty.

Measurement error is the difference between a measured value and the true value; it can be systematic (bias) or random.

A sampling plan specifies sample size (n) and acceptance number (c); lot acceptance is based on the number of nonconforming units in the sample.

Random sampling ensures every unit in the lot has an equal chance of being selected; it reduces bias.

A test procedure should include scope, references, equipment, calibration requirements, step-by-step instructions, acceptance criteria, and records.

Data recording should be contemporaneous, legible, indelible, and attributable to the person making the entry.

Corrections to recorded data should be made by a single line strike-through, initialed and dated, with the reason if required.

Electronic records must comply with applicable regulations (e.g., 21 CFR Part 11 for FDA) for integrity and audit trails.

Statistical process control (SPC) uses control charts to monitor process stability; points outside control limits indicate special-cause variation.

The operating characteristic (OC) curve of a sampling plan plots the probability of acceptance versus the lot fraction nonconforming.

Acceptance criteria are the specified limits or requirements used to determine conformity; they must be defined before inspection.

A nonconformance report (NCR) documents a departure from requirements and typically includes description, disposition, and corrective action.

Dispositions for nonconforming items include use-as-is, rework, repair, or reject; each requires appropriate approval.

An inspection report should identify the item inspected, the specification, the method, the results, the acceptance criteria, and the inspector.

Certificates of conformance (CoC) attest that the product meets specified requirements; they are not a substitute for test data unless specified.

Records must be retained for the period specified by contract, code, or regulation.

Final acceptance documentation often includes material test reports (MTRs), NDT reports, dimensional reports, and calibration certificates.

Traceability documentation links the finished product to the raw material and test records.

Personal protective equipment (PPE) is required when hazards cannot be eliminated by engineering or administrative controls.

Radiation safety for RT requires shielding, dosimetry, and compliance with local regulations (e.g., 10 CFR Part 34 for industrial radiography).

Ethical conduct requires honesty, impartiality, and avoidance of conflicts of interest; falsification of records is prohibited.

Quality assurance (QA) includes planned and systematic activities to ensure quality; quality control (QC) includes inspection and testing activities.

An audit is a systematic, independent examination to determine whether quality activities comply with planned arrangements.

Corrective action addresses the root cause of a nonconformity; preventive action addresses potential causes.

A quality manual documents the organization's quality policy, objectives, and procedures.

Inspectors must be qualified and certified to the applicable standard (e.g., ASNT SNT-TC-1A, ISO 9712) for the NDT method used.