neqsim-pipeline-survey-processing

name	neqsim-pipeline-survey-processing
calculation_basis	hybrid
version	0.1.0
description	Educational as-built pipeline survey processing that turns raw survey rows (KP, depth to top of pipe, seabed depth, easting/northing or latitude/longitude) into a cleaned, sign-normalised, resolution-filtered pipeline profile with flagged erroneous points, free-span and cover/burial candidates, a repeat-survey change comparison, a traceable processing log, and an elevation profile a NeqSim pipe model can consume. USE WHEN: a task needs a public, screening-level pipeline profile built from survey or inspection data before detailed DNV-RP-F105 free-span, DNV-RP-F109 on-bottom-stability, DNV-RP-F114 pipe-soil, or NeqSim thermal-hydraulic analysis.
last_verified	2026-08-10
requires	{"python_packages":[],"java_packages":[],"env":[],"network":[]}

Pipeline Survey Processing

A pipeline hydraulic or integrity model needs an elevation profile. The profile almost always starts life as a survey file: thousands of rows of KP, depth to top of pipe, seabed depth and coordinates, produced by a different discipline, in a different datum, with null markers, duplicated stations, sections that belong to a neighbouring line, and a handful of points that are simply wrong.

The step from that file to a usable profile is where the numbers are decided, and it is normally done by hand in a spreadsheet with no record of what was done. This skill makes that step explicit and repeatable: every filter, sign flip, projection and rejection is written into a processing log that travels with the result, so a reviewer can see how the profile in front of them was produced.

It stops at the profile. Free spans and burial intervals are reported as geometric candidates for a qualified assessment - it does not perform modal, VIV, fatigue or stability analysis.

When to Use

• A survey or inspection export must become a pipeline elevation profile for a NeqSim pipe model.
• Erroneous points, null markers or duplicated stations need to be identified before a profile is trusted.
• Only part of a surveyed line is in scope, and the section between two structures must be extracted with the trim recorded.
• Free-span or cover candidates need to be located along KP as input to a DNV-RP-F105 or DNV-RP-F114 assessment.
• Two surveys of the same line, taken years apart, need a like-for-like change comparison.
• The survey lacks outer diameter and a value has to be supplied manually with the override recorded as a data gap.

When Not to Use

• As a free-span assessment. Span candidates here are geometry only; modal response, VIV screening and fatigue belong to DNV-RP-F105 and to a qualified pipeline engineer.
• As a positioning or datum authority. This skill normalises a sign convention and projects coordinates for screening; it does not perform geodetic datum transformation and must not be used to reconcile survey datums.
• To conclude that a pipeline has moved. A change between surveys can be datum, tide, or survey uncertainty as easily as real movement.
• On confidential survey files in a public workspace. Inputs must be public, synthetic, or approved for open-source use.

Inputs

Input	Meaning
records	Survey rows, each a mapping with depth_to_top_m and either kp_m or a coordinate pair
depth_to_top_m	Depth to top of pipe, positive-down or negative-up - the convention is detected and normalised
seabed_depth_m	Optional seabed depth at the same station; required for span and cover screening
easting_m / northing_m	Optional projected coordinates; used to derive KP when it is absent
latitude_deg / longitude_deg	Optional geographic coordinates; swapped column order is detected and corrected, then projected
outer_diameter_m (row or argument)	Pipe outer diameter, from the survey or supplied as a user override
pipeline_id, survey_id	Identifiers carried into the result for traceability
start_kp_m, end_kp_m	Optional section trim, for example between a flowline end and a hot-tap
minimum_kp_spacing_m	Resolution filter; closer stations are dropped
outlier_threshold	Robust sigma multiple above which a point is flagged as erroneous
minimum_residual_m	Physical floor on the flagging residual, so survey noise is never flagged
smoothing_window	Odd rolling-median window used as the smoothing reference
span_gap_threshold_m	Gap above seabed at which a station counts towards a span candidate
change_threshold_m (compare)	Depth change above which a repeat-survey interval is reported

Outputs

Output	Contents
SurveyProfileResult.points	Retained, ordered, sign-normalised survey points
smoothed_depth_m	Rolling-median reference used for outlier detection
flagged_points	Erroneous points with KP, depth, residual and reason
kp_profile_m / elevation_profile_m	The profile itself, elevation being negated depth
route_length_m, max_slope_deg, slope_warning	Section length and slope screening (ok, watch, high)
span_candidates	Free-span candidates with start/end KP, length, max and mean gap
exposed_length_m, longest_span_m	Roll-up of the span candidates
buried_intervals, minimum_cover_m	Cover/burial intervals and the controlling minimum cover
outer_diameter_m, outer_diameter_source	Diameter and whether it came from survey, user_override or is missing
depth_convention	positive-down or negative-up as detected in the input
raw_point_count, retained_point_count, rejected_point_count	Filtering audit counts
processing_log	Every operation performed, in order
data_gaps	Missing evidence that a reviewer must close
SurveyComparisonResult	Common KP grid, per-station depth change, max lowering and lifting, changed intervals
to_neqsim_elevation_profile	Evenly spaced leg_positions_m and elevation_profile_m for a NeqSim pipe model

Engineering Method

Sign convention before anything else. Survey depths appear both as positive metres below sea level and as negative elevations. The convention is inferred from the sign of every depth in the file and normalised to positive-down; mixed signs are refused rather than guessed, because a silent sign error inverts every slope in the profile.

Validity, then order, then resolution. Non-finite values and the common survey null markers (-999, -999.25, -9999, 9999) are removed first. Rows are then sorted on KP and non-increasing stations dropped, so the profile is strictly monotonic. Only then is the resolution filter applied, keeping the first station of every minimum_kp_spacing_m window plus both endpoints - decimating before sorting would delete real stations and keep duplicates.

Erroneous points by robust residual. The depth series is compared against a rolling median, and a point is flagged when its residual exceeds outlier_threshold times a robust sigma derived from the median absolute residual (1.4826 x MAD). A median reference and a MAD scale are used rather than a mean and a standard deviation because a cluster of bad points would inflate both and hide itself. Points within half a smoothing window of each end sit on a truncated window, so their residual carries the local trend rather than an error; they are excluded from assessment instead of being flagged. Flagged points are reported, never silently deleted - a run of flags in one area is usually a survey-quality signal, not noise - but they are excluded from the span and cover geometry, because a depth that has been called wrong must not then be used to measure a gap.

Coordinates. Latitude/longitude columns are checked for swapped order, which is detectable because a latitude cannot exceed 90 degrees, then projected onto a local equirectangular frame about the first point. That is adequate for deriving KP and screening geometry over a flowline and explicitly not adequate for positioning work.

Spans and cover from one signed quantity. With both depths present, cover = depth_to_top - seabed_depth in the positive-down frame. Positive cover means the pipe top sits below the seabed and the station belongs to a burial interval; negative cover is a gap, and consecutive stations whose gap exceeds span_gap_threshold_m are grouped into a span candidate with its length, maximum and mean gap. Grouping consecutive stations, rather than counting points, is what makes the output comparable to a span list.

Repeat surveys on a common grid. Two processed surveys rarely share stations, so both are linearly interpolated onto a common KP grid over their overlap and differenced. Positive change means the pipe top sits deeper in the repeat survey. Intervals exceeding change_threshold_m are grouped and labelled lowering or lifting; the skill deliberately does not call this movement, because datum and tide differences produce the same signature.

Python Usage Pattern

from pipeline_survey_processing import PipelineSurveyProcessor

processor = PipelineSurveyProcessor(
    minimum_kp_spacing_m=5.0,
    outlier_threshold=4.0,
    minimum_residual_m=0.1,
    smoothing_window=11,
    span_gap_threshold_m=0.05,
)

records = [
    {"kp_m": 0.0, "depth_to_top_m": -298.4, "seabed_depth_m": -298.2},
    {"kp_m": 5.0, "depth_to_top_m": -298.2, "seabed_depth_m": -298.0},
    {"kp_m": 10.0, "depth_to_top_m": -999.25},          # null marker, removed
    {"kp_m": 15.0, "depth_to_top_m": -240.0, "seabed_depth_m": -297.7},  # flagged
    {"kp_m": 20.0, "depth_to_top_m": -297.5, "seabed_depth_m": -297.3},
]

result = processor.process(
    records=records,
    pipeline_id="1192-Y-101",
    survey_id="2010-survey",
    start_kp_m=0.0,
    end_kp_m=20.0,
    outer_diameter_m=0.3239,          # survey had no OD; recorded as a data gap
)

print(result.depth_convention)        # negative-up
print(result.rejected_point_count)
print([point.kp_m  point  result.flagged_points])
(result.span_candidates)
 entry  result.processing_log:
    (entry)


handoff = PipelineSurveyProcessor.to_neqsim_elevation_profile(result, section_count=)





older = processor.process(records=records, pipeline_id=, survey_id=)
change = processor.compare(baseline=older, repeat=result, change_threshold_m=)
(change.max_lowering_m, change.max_lifting_m, change.changed_intervals)

Validation Checklist

• The depth convention reported by the result matches the survey report.
• rejected_point_count is explainable: nulls, duplicates and resolution filtering account for it, and no unexpected bulk rejection occurred.
• Flagged points have been inspected rather than deleted, and clusters of flags are explained by a survey-quality note.
• The section trim matches the two structures the study is scoped to, and no neighbouring line is included.
• outer_diameter_source is survey, or the override is traced to a line list or pipe class entry.
• Every entry in data_gaps is closed or carried into the report as an open item.
• Span candidates are handed to a DNV-RP-F105 assessment before being quoted as free spans.
• A repeat-survey change is reconciled against datum, tide and positioning basis before it is described as pipeline movement.
• The processing log is stored with the profile in the task evidence.

Common Mistakes

• Decimating or smoothing before sorting on KP, which keeps duplicates and drops real stations.
• Detecting outliers with a mean and standard deviation, so a cluster of bad points raises the threshold and hides itself.
• Flagging on a robust sigma with no physical floor, so a smooth section reports centimetre-level noise as erroneous.
• Treating flagged points as noise to delete; they are frequently the finding.
• Flagging on a robust sigma with no physical floor, so a very smooth section reports centimetre-level survey noise as erroneous.
• Mixing positive-down depth and negative-up elevation in one file and letting the model average across the sign change.
• Reporting the count of stations above the gap threshold as the number of spans instead of grouping consecutive stations into intervals.
• Letting a point that has been flagged as erroneous set the maximum gap or the minimum cover.
• Using the projected coordinates from this skill for positioning or datum work.
• Comparing two surveys station by station without interpolating onto a common grid, so a KP offset appears as a depth change.
• Quoting a geometric span candidate as an acceptable or unacceptable span.

Limitations

• Screening only; it is not an as-built integrity assessment and it does not establish adequacy or compliance.
• No geodetic datum transformation, tide correction or positioning-uncertainty treatment.
• The smoothing reference is a rolling median, not the vendor spline that a survey processing package applies; residuals will differ in detail.
• Points within half a smoothing window of each end are not assessed for outliers, so an error at the very start or end of a section will not be flagged.
• A gap that spans a single station reports a length of zero, because span length is measured between the first and last gap station.
• Span candidates carry no modal, VIV, fatigue or stability content.
• Embedment is inferred from cover only; no soil model, lay-effect or remoulding is applied.
• The skill performs no file or network access; records are supplied by the caller.

References

• NeqSim: https://github.com/equinor/neqsim
• NeqSim Community Skills: https://github.com/equinor/neqsim-community-skills
• Companion skills: neqsim-pipe-route-profile, neqsim-bathymetry-profile-screening, neqsim-subsea-layout-geometry, neqsim-pressure-drop-screening
• NeqSim Java handoff: neqsim.process.equipment.pipeline.PipeBeggsAndBrills, neqsim.process.equipment.pipeline.TwoFluidPipe.setElevationProfile, neqsim.process.engineering.calculation.DnvRpF105FreeSpanScreeningKernel, neqsim.process.engineering.calculation.DnvRpF109OnBottomStabilityKernel, neqsim.process.engineering.calculation.DnvRpF114PipeSoilInteractionScreeningKernel
• Public standards for the downstream assessment: DNV-RP-F105 (free spanning pipelines), DNV-RP-F109 (on-bottom stability), DNV-RP-F114 (pipe-soil interaction).