This paper addresses automated mapping of the remaining wall thickness of metallic pipelines in the field by means of an inspection robot equipped with nondestructive testing (NDT) sensing. Set in the context of condition assessment of critical infrastructure, the integrity of arbitrary sections in the conduit is derived with a bespoke robot kinematic configuration that allows dense pipe wall thickness discrimination in circumferential and longitudinal direction via NDT sensing with guaranteed sensing lift-off (offset of the sensor from pipe wall) to the pipe wall, an essential barrier to overcome in cement-lined water pipelines. A tailored covariance function for pipeline cylindrical structures within the context of a Gaussian Processes has also been developed to regress missing sensor data incurred by a sampling strategy folllowed in the field to speed up the inspection times, given the slow response of the pulsed eddy current electromagnetic sensor proposed. The data gathered represent not only a visual understanding of the condition of the pipe for asset managers, but also constitute a quantative input to a remaining-life calculation that defines the likelihood of the pipeline for future renewal or repair. Results are presented from deployment of the robotic device on a series of pipeline inspections which demonstrate the feasibility of the device and sensing configuration to provide meaningful 2.5D geometric maps. K E Y W O R D S gaussian process, inspection harsh environments, mapping, NDT, pipeline robot 1 | MOTIVATION-A TAXONOMY OF NDT INSPECTION TECHNIQUES Nondestructive testing (NDT) or evaluation (NDE) is extensively used by the energy and water industry to assess the integrity of their network assets, particularly their larger and most critical conduits (generally refered to as those larger than 350 mm in diameter), in their decision-making process leading their renewal/repair/rehabilitation programs. The key advantage of NDT/NDE is that the structure of the asset is not compromised in estimating its condition. The sensing modality to use is strongly influenced by the material of the asset. Grey Cast Iron (CI) pipelines remain the bulk of the buried critical water infrastructure in the developed world as that was the material of choice for mass production with the advent of the Industrial Revolution in the middle of the 18th century (alongside its less brittle relative of Ductile Iron since 1950s), until carbon steel, asbestos cement, or plastic pipelines (PVC) among other materials made them redundant over the years. The nonhomogeneity of the CI produce means that sensing techniques widely used in the (mild) carbon steel networks in the energy pipeline sector, such as ultrasonics or electromagnetic acoustic transducers, are inadequate for CI, and the underlying techniques of most commercial propositions for CI are instead based on either magnetics (e.g., magnetic flux leakage, pulsed eddy current [PEC], and remote field eddy currents), or the study of the propagation of pressure waves in the pipeline...