ISO 13916 Preheat, Interpass, and Heat Retention Temperature Measurement Guidelines in Cladding Manufacturing

1. Definition and Fundamental Principles

ISO 13916, titled "Welding — Guidelines for measurement of preheat temperature, interpass temperature and heat retention temperature," is the international reference standard governing the methodology by which thermal conditions are quantified during welding operations. In the context of bimetallic cladding and weld overlay fabrication, this standard establishes the authoritative framework for determining where temperatures are measured, how they are measured, what instrument accuracy is required, and how data must be recorded and reported.

The fundamental principle underlying ISO 13916 is that temperature control is not merely a procedural formality — it is a metallurgical necessity. In cladding operations, particularly those involving dissimilar material combinations such as carbon steel substrates with austenitic stainless steel or nickel-alloy overlays, the thermal history of the joint directly governs:

• Preheat temperature: The minimum temperature to which the base material must be raised before welding commences, to reduce cooling rates, minimize hydrogen-induced cracking susceptibility, and limit residual stress gradients.
• Interpass temperature: The maximum temperature permitted between successive weld passes or layers, ensuring that each subsequent deposit is deposited onto a substrate that has not exceeded a critical thermal threshold that could degrade microstructural integrity.
• Heat retention temperature: The minimum temperature that must be maintained during and after welding (particularly during post-weld heating or slow cooling phases) to facilitate hydrogen diffusion and prevent delayed cracking.

ISO 13916 addresses the measurement of all three thermal parameters as a unified system, recognizing that the validity of any single measurement depends on consistent methodology across the entire thermal control sequence.

2. Category and Business Positioning

Within the capability taxonomy of Cladding Technology Shanxi Co., Ltd., ISO 13916 is classified under Category 362: Execution Standards — Temperature Control, with the technical direction designated as "Temperature Measurement Basis" (测温依据). This positioning is significant for several reasons:

• Foundational status: ISO 13916 serves as the overarching methodological standard for temperature control. It does not prescribe specific temperature values — those are determined by material-specific standards such as ASME Section IX, AWS D10.9, or NACE MR0175. Rather, ISO 13916 prescribes the method by which any prescribed temperature is verified.
• Cross-process applicability: Unlike process-specific standards that apply only to welding, ISO 13916's measurement principles extend to all thermal processes within the company's scope, including post-bonding heat treatment in hydraulic explosive bonding and thermal conditioning in explosion welding.
• Qualification backbone: In WPS (Welding Procedure Specification) and PQR (Procedure Qualification Record) development, temperature measurement methodology is audited by third-party certification bodies. Non-conformance with ISO 13916 renders all associated thermal data invalid, potentially voiding procedure qualifications.

3. Technical Purpose and Value

The primary technical purpose of implementing ISO 13916 is to ensure compliance of temperature measurement methods (测温方法合规), which translates into the following measurable business and technical values:

3.1 Metallurgical Assurance

Accurate temperature measurement ensures that thermal cycles remain within the bounds defined by the qualified WPS. For example, in a 309L/316L transition layer weld overlay on a carbon steel substrate, the interpass temperature must typically not exceed 250°C. A measurement error of ±15°C — well within the tolerance of an uncalibrated infrared thermometer — could allow a pass to be deposited at 265°C, promoting grain boundary carbide precipitation and reducing corrosion resistance in the overlay.

3.2 Regulatory and Certification Compliance

ISO 13916 compliance is a prerequisite for:

• ASME Section IX PQR documentation
• API 922/923 personnel and procedure qualification records
• ISO 3834 quality management system audits
• NB/T 47014 procedure qualification records for pressure vessels
• EN 1090 structural welding documentation

3.3 Risk Mitigation

Systematic temperature measurement per ISO 13916 reduces the risk of:

• Hydrogen-induced cold cracking (HIC) in high-strength steels
• Excessive grain growth in overlay deposits
• Residual stress exceedance leading to distortion or fatigue failure
• Disqualification of production batches due to documentation deficiencies

4. Key Process and Implementation Points

4.1 Measurement Location Requirements

ISO 13916 specifies that temperature measurements must be taken at locations that are representative of the thermal condition at the weld zone. The following location rules apply:

Parameter	Required Measurement Location	Minimum Distance from Weld	Maximum Distance from Weld
Preheat Temperature	Surface of base material, adjacent to the weld preparation area	—	Not less than 100 mm from the weld line (for plates ≤ 25 mm thickness)
Interpass Temperature	Surface of the most recently deposited weld metal, at the location of the next pass	—	—
Heat Retention Temperature	Thickest section of the weld assembly, at the weld centerline or nearest accessible point	—	—

For clad plate and pipe assemblies, additional considerations apply:

• In multi-layer overlay builds, the interpass temperature must be measured on the surface of the last completed layer, not on the base metal, as the thermal mass of the overlay stack creates a different cooling profile.
• For pipe cladding with circumferential welds, measurements should be taken at the thickest section of the joint (typically the weld reinforcement area) and at a minimum of two diametrically opposed locations.
• When measuring through insulation or refractory backing, the sensor must be in direct contact with the metal surface; readings through intervening materials are not acceptable per ISO 13916.

4.2 Measurement Methods

ISO 13916 recognizes two primary measurement methods and defines their applicability:

Method	Applicability	Advantages	Limitations	Recommended Use in Cladding
Direct Contact (Thermocouple / RTD)	All welding processes; all temperature ranges up to 1500°C	High accuracy (±1–2°C); continuous recording; traceable calibration	Requires surface preparation; potential for sensor damage at high temperatures; limited to accessible surfaces	Primary method for preheat and interpass monitoring in TIG/MIG weld overlay
Non-Contact (Infrared Pyrometer / Thermal Imaging)	Temperatures above 100°C; inaccessible surfaces	No surface contact required; rapid readings; safe for high-temperature zones	Emissivity dependency (±5–10°C typical error); affected by surface condition (oxide, paint, spatter); not suitable for temperatures below 50°C	Supplementary method for heat retention monitoring; verification of preheat uniformity across large plates

4.3 Instrument Accuracy Requirements

ISO 13916 mandates that temperature measurement instruments must meet minimum accuracy criteria relative to the tolerance specified in the applicable WPS or procedure:

• Thermocouples: Type K (chromel-alumel) is the minimum recommended type for welding temperature measurement, with an accuracy of ±1.5% of reading or ±2°C, whichever is greater. Type J or Type E are generally not acceptable for qualification purposes.
• Calibration interval: Thermocouple assemblies must be calibrated at intervals not exceeding 12 months, or more frequently if used in high-vibration or high-temperature environments.
• Infrared pyrometers: Must have a stated emissivity setting appropriate for the material being measured (typically 0.85–0.95 for oxidized carbon steel surfaces; 0.90–0.95 for stainless steel). The instrument accuracy should be ±2% of reading or ±3°C, whichever is greater.
• Data logging: Where continuous monitoring is required (e.g., during post-weld heat treatment for hydrogen bake-out), data loggers with a resolution of ±0.5°C and a sampling rate of at least 1 reading per minute are required.

4.4 Documentation and Record Requirements

ISO 13916 requires that all temperature measurements be documented in a manner that enables traceability and audit. The minimum record content includes:

1. Instrument identification: Serial number, type, calibration date, and next calibration due date.
2. Measurement location: Precise description or sketch indicating where on the assembly the measurement was taken.
3. Temperature value: Recorded to the nearest 1°C.
4. Time stamp: Date and time of measurement.
5. Operator identification: Name or badge number of the person taking the measurement.
6. Reference to WPS: The procedure specification number and the temperature limit being verified against.
7. Deviation notation: Any reading that falls outside the specified tolerance must be annotated with corrective action taken.

5. Applicable Standards and Acceptance Criteria

5.1 Primary Standard

ISO 13916:2019 — Welding — Guidelines for measurement of preheat temperature, interpass temperature and heat retention temperature. This is the current edition and supersedes ISO 13916:1997.

5.2 Related Standards Referenced by ISO 13916

Standard	Relevance
ISO 9606-1	Qualification testing of welders — welding processes (includes temperature requirements)
ASME Section IX	Welding, Brazing, and Bonding Qualifications — QW-400 through QW-460 cover preheat and interpass temperature rules
AWS D10.9	Qualification of Welding Procedures for Weld Overlay — specifies temperature measurement requirements for overlay applications
GB/T 985.1	Welding procedure specification rules (Chinese national standard incorporating ISO principles)
NB/T 47014	Rules for welding procedure qualification of pressure vessels — references temperature measurement per GB/T 985.1
ISO 3834-2	Quality requirements for fusion-welding of metallic materials — requires documented temperature control per ISO 13916
EN ISO 15614-1	Specification and qualification of welding procedures — includes thermal parameter documentation

5.3 Acceptance Criteria for Temperature Measurement Compliance

The following criteria determine whether temperature measurement practice complies with ISO 13916:

1. All thermocouples used for qualification testing must have a valid calibration certificate traceable to a national metrology institute (NMI).
2. The measurement location must be within the zone defined by the WPS (typically within 25 mm of the weld line for preheat, or on the weld surface for interpass).
3. Temperature readings must be taken at steady state — the thermocouple must have been in contact with the surface for a minimum of 30 seconds before the reading is recorded.
4. For preheat verification, the temperature must be measured after the heating cycle has stabilized, not during the ramp-up phase.
5. Any temperature reading that exceeds the specified interpass limit invalidates the subsequent pass until the assembly has cooled below the limit.
6. Records must be retained for a minimum of 10 years (or as specified by the applicable product standard) to support traceability.

6. Common Risks and Controls

Risk	Description	Control Measure
Thermocouple drift	Long-term exposure to high temperatures causes thermocouple wire degradation, leading to systematic reading errors	Implement a 6-month calibration cycle for thermocouples used in high-temperature applications (>400°C); use reference-grade Type N or Type S thermocouples for critical applications
Incorrect measurement location	Measuring at a point too far from the weld zone, where the temperature is lower than at the actual weld site	Use marked measurement zones on the assembly; train operators on location requirements per ISO 13916; use multiple thermocouples in thick-section welds
Emissivity error in IR measurements	Infrared pyrometer readings are inaccurate if the emissivity setting does not match the actual surface condition	Apply high-emissivity tape (ε = 0.95) to the measurement area before taking IR readings; calibrate IR pyrometers against contact thermocouple readings at regular intervals
Record incompletion	Missing time stamps, operator IDs, or instrument calibration data in temperature logs	Use digital data loggers with automatic time-stamping; implement a two-person verification system for qualification records; conduct internal audits per ISO 3834-2
Interpass temperature exceedance	Welding continues after the interpass temperature has exceeded the WPS limit, potentially degrading overlay microstructure	Install continuous monitoring with audible alarms at 80% of the interpass limit; enforce mandatory cooling intervals; use thermal imaging for real-time monitoring of multi-pass welds
Cold preheat measurement	Preheat temperature is measured before the assembly has reached thermal equilibrium, resulting in a falsely low reading	Allow a minimum of 5 minutes of stabilization time after heating before taking the reading; use a thermocouple with a data logger to confirm the temperature has plateaued

7. Application Scenarios Across Technology Routes

7.1 TIG/MIG Weld Overlay

In TIG (GTAW) and MIG (GMAW) weld overlay operations, ISO 13916 compliance is most critical during the following phases:

• Preheat verification: For overlay of austenitic stainless steel (e.g., 309L, 316L) onto low-alloy or carbon steel substrates, preheat temperatures of 50–150°C are typically required to prevent cracking in the dilution zone. ISO 13916 dictates that the thermocouple be placed on the base metal surface, within 25 mm of the weld preparation, after the heating cycle has stabilized.
• Interpass monitoring in multi-layer builds: Transition layer overlay builds (e.g., 309L → 316L → 625) typically involve 3–5 layers. The interpass temperature between layers must not exceed 250°C for austenitic stainless steels. A Type K thermocouple attached to the surface of the last completed layer, with continuous data logging, is the standard approach.
• Post-weld heat retention: For nickel-alloy overlays (e.g., Hastelloy C-276, Inconel 625) on carbon steel, a post-weld bake-out at 150–250°C for 1–2 hours is required to diffuse residual hydrogen. ISO 13916 requires that the heat retention temperature be measured at the thickest section of the weld, with the reading taken after the assembly has reached the target temperature.

Practical example: For a TIG weld overlay of 309L on a Q345R carbon steel pipe, the WPS specifies a preheat of 100°C ± 20°C and an interpass maximum of 250°C. Per ISO 13916, the preheat temperature is measured using a calibrated Type K thermocouple placed on the pipe surface, 50 mm from the weld line, after 10 minutes of stabilization. The interpass temperature is measured on the surface of the previous pass using the same thermocouple, with readings taken immediately before the next pass is initiated. All readings are logged with instrument ID, time stamp, and operator name.

7.2 Hydraulic Explosive Bonding

In hydraulic explosive bonding (also known as hydraulic explosion cladding), the bonding process itself is a solid-state mechanical process that does not involve welding heat input. However, ISO 13916 temperature measurement principles apply in the following contexts:

• Pre-bonding surface preparation: If the base material requires preheating for surface cleaning (e.g., flame cleaning of oxide scale), the preheat temperature must be measured per ISO 13916 to ensure the base metal is not overheated, which could compromise the bonding interface.
• Post-bonding heat treatment: Some bonded assemblies require stress-relief annealing. The heating and cooling rates, as well as the soak temperature, must be monitored using thermocouples placed per ISO 13916 location requirements. For example, a stress-relief anneal at 600°C for 2 hours requires continuous temperature logging at the thickest section of the assembly.
• NDT thermal methods: Thermal imaging (infrared thermography), which operates on the same principles as IR pyrometry, is used for defect detection in bonded interfaces. The emissivity calibration and measurement protocols follow ISO 13916 non-contact measurement guidelines.

7.3 Explosion Welding

Explosion welding involves the detonation of explosives to accelerate a cladding sheet onto a base plate at high velocity, creating a solid-state bond. ISO 13916 temperature measurement is relevant in the following ways:

• Pre-assembly temperature control: The base plate and cladding sheet must be at controlled temperatures before the explosion event. If the materials are preheated (e.g., to reduce brittleness in cold-weather conditions), the preheat temperature is measured per ISO 13916. Typically, the assembly temperature should be within ±10°C of the specified value to ensure consistent bonding parameters.
• Post-explosion thermal monitoring: The explosion event generates localized temperatures at the bonding interface that can exceed 2000°C momentarily. While these temperatures are not directly measured, the residual heat in the assembly after the event must be monitored to determine when the assembly is safe to handle and when post-explosion stress-relief can begin.
• Stress-relief annealing after explosion: Explosion-welded clad plates typically require stress-relief annealing at 600–750°C for 1–4 hours, depending on the material combination. ISO 13916 governs the placement of thermocouples, the accuracy requirements for temperature control, and the documentation of the thermal cycle. For large plates (>3000 mm × 2000 mm), multiple thermocouples are placed at corners, edges, and center to ensure uniform heating, with all readings logged continuously.

Practical example: For an explosion-welded 316L/C-276 clad plate (2000 mm × 1000 mm × 50 mm), the post-explosion stress-relief anneal requires a soak temperature of 650°C ± 25°C. Per ISO 13916, six Type K thermocouples are embedded at the plate corners and center, with data logged at 1-minute intervals. The heating rate must not exceed 150°C/hour to prevent differential thermal expansion between the cladding and base material. The soak time begins only when all six thermocouples have reached the target temperature, and the assembly is held at temperature for a minimum of 2 hours before controlled cooling at ≤ 100°C/hour.

8. Contribution to Qualification Building, Product Delivery, and Customer Value

8.1 Qualification Building

ISO 13916 compliance is a prerequisite for all welding procedure qualifications (WPS/PQR) developed by Cladding Technology Shanxi Co., Ltd. Specifically:

• ASME Section IX PQRs: Temperature measurement data per ISO 13916 is mandatory for QW-400 through QW-460 documentation. Without compliant temperature records, PQRs cannot be issued, and production welding cannot proceed under the qualified procedure.
• AWS D10.9 overlay qualifications: The standard explicitly requires that preheat and interpass temperatures be measured and recorded in accordance with recognized measurement guidelines. ISO 13916 is the internationally accepted reference.
• ISO 3834 quality system certification: The company's ISO 3834-2 certification audit includes verification of temperature measurement practices. Non-conformance with ISO 13916 would result in a major non-conformance finding, potentially leading to suspension of the certification.
• EN 1090 structural welding: For structural steel cladding applications, EN 1090 requires documented temperature control per ISO 13916 as part of the welder and procedure qualification package.

8.2 Product Delivery

Compliant temperature measurement directly impacts product delivery in the following ways:

• First-pass yield improvement: Accurate temperature control reduces the incidence of welding defects (cracks, porosity, excessive dilution), leading to higher first-pass yield and reduced rework. Industry data suggests that proper temperature control can reduce welding defect rates by 30–50% in overlay applications.
• Reduced schedule delays: When temperature records are complete and compliant, there are no delays in final inspection and documentation review. Incomplete or non-compliant records can delay product release by weeks while the company attempts to retroactively document or requalify procedures.
• Traceability for customer audits: End users in the oil and gas, power generation, and marine industries routinely audit the temperature control records of clad plate and pipe suppliers. ISO 13916-compliant records provide immediate confidence in the manufacturing process and reduce the time and cost of customer audits.

8.3 Customer Value

The implementation of ISO 13916 delivers measurable value to the company's customers:

1. Extended service life: Proper temperature control during overlay welding ensures optimal microstructure in the overlay, resulting in superior corrosion and wear resistance. This translates directly into longer service life and reduced maintenance costs for the end user.
2. Reduced warranty claims: Temperature-related defects (cold cracks, intergranular corrosion, excessive dilution) are among the most common causes of warranty claims in cladding products. ISO 13916 compliance virtually eliminates this failure mode.
3. Regulatory acceptance: For products used in regulated industries (nuclear, pressure vessels, offshore platforms), ISO 13916-compliant temperature records are a regulatory requirement. Customers cannot accept products without this documentation.
4. Competitive differentiation: In a market where many competitors rely on informal or undocumented temperature measurement practices, Cladding Technology Shanxi Co., Ltd.'s rigorous adherence to ISO 13916 serves as a competitive differentiator, particularly in bid evaluations where quality documentation is a scoring criterion.

9. Implementation Recommendations for Cladding Technology Shanxi Co., Ltd.

9.1 Immediate Actions

1. Audit current thermocouple inventory: Verify that all thermocouples in use are Type K or higher, with valid calibration certificates traceable to a national metrology institute. Replace any instruments with expired calibrations or accuracy below ±2°C.
2. Standardize measurement locations: Develop a standardized location chart for each product type (clad plate, clad pipe, overlay repair) showing the exact thermocouple placement points per ISO 13916. Post these charts at each welding station.
3. Implement digital data logging: Transition from manual paper-based temperature records to digital data loggers with automatic time-stamping and instrument ID capture. This eliminates the most common source of documentation non-conformance.

9.2 Medium-Term Actions

1. Develop a temperature measurement SOP: Create a site-specific standard operating procedure that references ISO 13916 and provides step-by-step instructions for operators, including instrument selection, location marking, reading verification, and record completion.
2. Train all welding operators and QC inspectors: Conduct annual training on ISO 13916 measurement requirements, including hands-on practice with thermocouple placement and IR pyrometer calibration. Maintain training records as part of the ISO 3834 quality system.
3. Integrate temperature monitoring into the MES: Connect data loggers to the Manufacturing Execution System to enable real-time monitoring of temperature parameters and automatic alerts when readings approach WPS limits.

9.3 Long-Term Strategic Actions

1. Pursue ISO 13916-based procedure qualification library: Build a comprehensive library of qualified WPS/PQR packages, each with fully documented temperature control per ISO 13916, covering all material combinations and thickness ranges in the company's product portfolio.
2. Develop automated thermal monitoring for explosion welding: Invest in embedded thermocouple systems for explosion-welded assemblies that can monitor the entire thermal cycle from pre-assembly through post-explosion stress relief, providing a complete thermal history for each production batch.
3. Establish a temperature measurement calibration laboratory: Develop in-house calibration capability for thermocouples and IR pyrometers, reducing dependence on external calibration services and ensuring faster turnaround for instrument maintenance.

10. Conclusion

ISO 13916 is not merely a documentation standard — it is the technical foundation upon which the metallurgical integrity of every cladding product manufactured by Cladding Technology Shanxi Co., Ltd. depends. From the first preheat measurement on a carbon steel substrate to the final heat retention reading after a nickel-alloy overlay, the accuracy and compliance of temperature measurement directly determine whether the product will perform as specified throughout its service life.

By rigorously implementing ISO 13916 across all three technology routes — TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding — the company builds a qualification framework that meets the most demanding international standards, delivers products with superior reliability, and provides customers with the traceability and confidence they require in regulated and safety-critical applications.

The investment in ISO 13916 compliance — in instruments, training, documentation systems, and procedural discipline — yields returns in the form of reduced defects, faster qualification cycles, stronger customer relationships, and a competitive position that is difficult for less rigorous competitors to replicate.