Advancing geohazard management through use of direct stress measurement inline inspection

By ROSEN Group

Introduction

Geohazards such as landslides, flooding, erosion, and subsidence pose major threats to pipeline integrity, often introducing loads beyond original design assumptions – especially for aging infrastructure lacking modern welding practices and advanced understanding of geohazards. Climate change has amplified these risks through more frequent extreme weather events, highlighting the need for proactive, data-driven geohazard management. Axial strain, a key loading mechanism from ground movement and operational conditions, can lead to buckling or tensile girth weld failure when strain capacity limits are exceeded. Historically difficult to measure directly, axial strain has relied on indirect methods combining structural analysis and inertial measurement unit (IMU) data. Emerging in-line inspection technologies, such as ROSEN’s micromagnetic hysteresis technology (MHT), enable direct stress measurement and yield strength determination, advancing geohazard monitoring and integrity management. This has the potential to enhance pipeline safety and support informed integrity decisions.

Causes of Axial Loading in Pipelines

Axial loading in pipelines can arise from construction, operational conditions, and external forces. During installation, loads are typically minimal, but methods like horizontal directional drilling (HDD) can induce complex stress regimes involving tensile, bending, and external pressure loads, sometimes in areas of the pipeline that were not predicted by standard approaches [i & ii ]. Conventional excavation may cause bending strains from uneven trenching or horizontal misalignment, while thermal stresses from solar heating or temperature fluctuations can induce further strain. External loads from geohazards, such as landslides, riverbank erosion, seismic activity, subsidence, frost heave, and buoyancy in organic soils, can impose significant axial strain without noticeable deflection detectable by IMU tools (Figure 1).

Figure 1: Axial loading from ground movement parallel to the pipeline with minimal bending.

Anthropogenic activities, including mining subsidence (Figure 2), civil works, and engineered slope failures, can also contribute to axial loading. These mechanisms highlight the complexity of predicting strain and the need for advanced monitoring to manage integrity risks effectively.

Figure 2: Upheaval buckling from mining subsidence

Geohazard Management Plans

Management of geohazards affecting pipelines has long lacked practical guidance, with most standards acknowledging threats but offering few actionable methods. ISO 20074 [iii] marked a major shift by introducing a lifecycle framework for geohazard identification, risk assessment, and mitigation, requiring operators to maintain geohazard management plans throughout a pipeline’s life. Regulatory focus has intensified: CER issued advisories after girth weld failures at strains as low as 0.4% [iv], and API RP 1187 [v] further advances landslide-specific guidance, reflecting a trend toward prescriptive approaches. Despite these developments, direct axial strain measurement remains challenging; IMU data only captures bending strain, leaving axial forces undetected. Current methods include strain gauges for localized measurement and residual stress techniques, or predictive modeling via finite element analysis (FEA) integrating IMU with ground models based on remote sensing and geotechnical data. While structural analysis is widely used, uncertainties persist, underscoring the need for improved direct axial strain measurement to support robust, data-driven geohazard management.

MHT In-line Inspection – Axial Stress & Strain Determination

Recent ILI advancements include axial stress and strain tools, enabling direct measurement of pipeline stress/strain subjected to external loads. Despite being available for over a decade, industry adoption remains limited compared to traditional calculated fitness-for-service methods.

Micromagnetic hysteresis technology (MHT) is a novel ILI tool designed to measure uniform longitudinal stress in pipelines, including geohazard-induced loads, while also determining material properties (Figure 3).

Figure 3 ROSEN’s Micromagnetic Hysteresis Technology ILI Tool

MHT uses a magnetic yoke with excitation and receiving coils to generate hysteresis curves (Figure 4), encoding stress history and mechanical properties.

Figure 4 Schematic of micromagnetic sensor (left) and an example hysteresis loop in the specimen, measured as a sensor response

The MHT sensor is sensitive to stress applied to the pipeline material and the signal response is monotonically dependent on that applied stress, demonstrated by the differing hysteresis curve shapes when a zero-stressed specimen is subjected to tensile loading of up to 8 N/mm2, shown in Figure 4. Elastic stresses can be quantified via the modulus of elasticity of steel, and it has been identified that the sensor has potential to quantify strains that exceed the elastic limit.

Figure 5 Change in hysteresis curve when tensile load applied to ferromagnetic material

Additionally, the MHT sensor can determine yield strength, necessary for a range of fitness for service assessments and a requirement of CFR §192.607 [vi]. The coercivity of a material – defined as the magnitude of the applied magnetic field required to reduce its magnetization to zero following saturation – is one of the most prominent characteristic values derived from the magnetic hysteresis curve and is commonly used for material characterization. Coercivity is influenced by microstructural features such as grain size, inclusion content, and dislocation density, which also govern mechanical properties like strength and hardness. Consequently, empirical correlations between coercivity and specific material properties are observed.

Combination of MHT with Conventional ILI Technologies

Axial forces can cause, and adversely affect, pipeline anomalies. The presence of an anomaly within regions of longitudinal strain can significantly reduce the compressive strain capacity (CSC) and tensile strain capacity (TSC) of a pipeline, increasing susceptibility to failure. Metal loss lowers both CSC and TSC, while circumferential anomalies reduce TSC and axial anomalies reduce CSC. Geometric anomalies – such as dents, wrinkles, and ovalities – can initiate local buckling (Figure 6) and often indicate geohazard loading.

Combining MHT with caliper tools enables detection of subtle deformations within high-strain zones, supporting proactive integrity management.

Integrated with other ILI technologies (MFL, EMAT, UT), MHT data enhances susceptibility models for girth weld defects and circumferential stress corrosion cracking (CSCC). Coupling IMU bending strain with longitudinal stress improves CSCC risk assessment, aiding early identification and failure prevention.

Integration of MHT into Geohazard Management Programs

Integrating MHT into geohazard management enhances threat identification, evaluation, and monitoring. Unlike IMU, MHT detects axial loads that may occur without significant displacement or below typical bending strain thresholds, enabling earlier identification of geohazard threats. For threat evaluation, MHT provides direct stress measurements, eliminating reliance on predictive modeling and reducing uncertainty in integrity assessments. This empirical data establishes accurate baselines for forecasting future loading and informs mitigation strategies. For monitoring, MHT complements existing methods such as strain gauges and IMU by offering continuous, high-resolution stress data, improving characterization of load accumulation over time. Incorporating MHT into geohazard programs aligns with ISO 20074 and API RP 1187 guidance, supporting proactive, data-driven integrity management.

Discussion

Axial strain from geohazards, construction, and operational loads presents complex integrity challenges, amplified by climate-driven extreme events. Conventional methods like IMU and strain gauges provide partial insights but fail to capture total longitudinal strain, leaving uncertainty in fitness for service evaluations. ROSEN’s MHT addresses this gap by directly measuring axial and bending components, and determining yield strength, meeting regulatory requirements and improving assessment accuracy. Combined with conventional ILI tools, MHT enhances threat identification, evaluation, and monitoring, enabling proactive, data-driven geohazard management and advancing the industry toward predictive integrity strategies.

References

i. PRCI. Installation of pipelines by horizontal directional drilling, an engineering design guide. CNST-1-3. Catalog no. PR-277-144507-E01. September 23, 2015. ii. Faghih, A., et al. Stress analysis of steep pipe installation in horizontal directional drilling based on strain monitoring. Tunnelling and Underground Space Technology (105673), Volume 147, May 2024. iii. ISO 20074. Petroleum and natural gas industry - Pipeline transportation systems – Geological hazard risk management for onshore pipelines. Geneva: International Organisation for Standardisation. 2019. iv. Canada Energy Regulator. Safety Advisory SA2020-01 – Girth Weld Area Strain-Induced Failures: Pipeline Design, Construction, and Operation Considerations. 12 February 2020. v. API RP 1187. Pipeline Integrity Management of Landslide Hazards. American Petroleum Institute (API) Recommended Practice, First Edition, Washington, DC, 2024.

Figure 6 Buckling caused by ground movement aligned along pipe axis