Table of Contents
1 Scope
2
2 Purpose
2
3 Safety
2
4 References
2
5 Inspection Guidelines
4
6 Detailed Inspection Guidelines
5
1
Scope
This procedure guidelines for inspecting above ground storage tanks that have been placed in service. 2
Purpose
This procedure to assist the API Inspectors of Tank Inspection Units in their selection by providing Typical Plans and inspection
checklist
all types of existing storage tank, on stream evaluation, and tracking
for of
existing equipment condition. 3
Safety
3.1 Radiographic examination personnel safety should be per general industrial
standard and that of specific industry requisite.
3.2 All pressure testing should be in compliance with guidelines established by the company and that of the concerned industry’s
safety
guide lines.
3.3 Use of personnel protection equipment and safe entry for inspection is the responsibility of the inspector/Inspection Engineer 4
References
The following standards were used in the preparation of these inspection guidelines and should be carefully reviewed by the inspectors/inspection engineers prior to performing inspection. All references should be the latest issued revision or edition. American Society of Mechanical Engineers ASME SEC V Nondestructive Examination ASME SEC VIII Boiler and Pressure Vessel Code
American Petroleum Institute API STD 510 Pressure Vessel Inspection Code
API RP 571 Damage Mechanism Affecting fixed Equipment API RP 580 Risk Based Inspection API RP 578 Material Verification API STD 620 Design and construction of Large, Welded, Low Pressure Storage Tanks API STD 650 Welded Steel Tanks for Storage API STD 653 Tank Inspection, Repair, Alteration and Reconstruction NBIC National Board Inspection Code
5
Inspection Guidelines
These guidelines are intended for inspectors and inspection engineers. Generally, the steps for storage Tank inspection are shown in the Flowchart in Inspection
attachment-A. Equipment shall be inspected per Typical Plan (TIP) and Checklist (detailed check list of API 653 shall
be the guide) shown in attachment B and C respectively.
5.1 Check the tank drawing, construction codes, and material of construction, internal
parts, and dimensions
(diameter,
height
and
thickness).
5.2 Read the tank file and note history of corrosion, repairs and replacement if any.
5.3 Carry out joint inspection (check includes ventilation, blinds, scaffolds and
lighting) and obtain entry permit to ensure the Tank is safe to enter
and inspect. At the time of inspection keep a man watch for your safety.
5.4 Primarily carry out external inspection for external leaks, external damage, insulation or paint damage, external corrosion.
5.5 Ensure the tank is isolated with proper blinds. Obtain entry permit from operation. Prior to internal inspection entry gas test to make sure no toxic
gases are released. While entry to the tank, have a man stand by at the man way for personnel safety and company loss prevention.
5.6 Start preliminary inspection at all man ways (man way inspection) going from
bottom (all around) to the top. Record the observations on a
note pad at
each level. Start entering the tank from the bottom man
way and assess the
conditions
tank shell plates, tank internal
of nozzles, tank bottom plates,
hardware’s
(Columns,
supports / legs, sumps, etc.). Identify each item and
float,
note
the
observations for your inspection evaluation. 6
Detailed Inspection Guidelines
While
performing
erosion/corrosion, mechanical
detailed
inspection
look
for
pitting
corrosion,
channeling, weld erosion/corrosion and cracks,
damages while opening and closing, environmental cracking,
bulging and blistering and the like are some that will be noted with in the tanks. Coating
conditions, if coated. A good cleaning and careful
evaluation will help make a good decision. Sometime Fitness for Service inspection (FFS) assessment will
be
required
and
evaluation will have to be done from design, operation, and history
full of
operation to increase the service life of the tank.
6.1
Actual Thickness Determination of shell and shell penetrations
6.1.1 A general UT thickness survey of a tank shell will typically require a grid system as noted below. (Shell thickness gauging shall preferably be done by remote controlled UT crawler machines.) a, Mark vertical lines from the reference points at the bottom of shell to the top of shell. Number of reference points around circumference is 8,12,16,20 and 24 for tank diameters less than 12 meters, between 12 and 20 meters, between 21 and 27 meters, between 28 and 36 meters, 36 meters and above, respectively.
b, Mark two horizontal grid lines on each shell course, the first one at 300 mm above the lower edge of each course, and the second one at mid-height of each course. Number horizontal grid lines 01, 02, 03 etc. starting with 01 at 300 mm above tank bottom. c, In areas of significant external pitting, the depth should be measured with a pit gauge and subtracted from the shell thickness adjacent to the pit, to obtain the remaining thickness at the bottom of the pit. Visual inspection is to be carried out to locate locally corroded and pitted areas prior to ultrasonic gauging d, Ultrasonic thickness readings shall be taken at the intersection of vertical and horizontal grid lines. e, Ultrasonic thickness measurements of nozzles and man way neck plates should be taken as close as possible to the reinforcing or shell plate at 12, 3, 6 and 9 O’clock positions. 6.1.2 The amount of inspection can be increased further, if appropriate, based on the initial evaluation results. 6.1.4 At any location where readings are less than 90% of original thickness or thinning is equal to or more than 1 mm from the original thickness, the adjacent area shall be UT scanned to determine the extent of corrosion.
6.2
Condition Determination of Tank bottom
6.2.1 During inspection, the entire floor should be visually examined for
holes,
cracked
welds,
and
any
areas
that
were previously
repaired. 6.2.2 Bottom plate UT thickness readings shall be taken at least as detailed below a, MFL shall be made over the entire bottom plates to identify thinned areas b, Carry out hand scan or UT scanning on all inaccessible areas c, Perform UT follow up or back up. 6.2.3 Bottom plates and bottom sump shall be 100% vacuum tested for all weld joints including shell to bottom joints. 6.2.4 UT scanning shall be performed for Tank Sump.
6.2.5 MPI shall be performed at shell to annular plate joints.
6.3
Condition Determination of Tank Roof
6.3.1 Visual checks will locate areas of especially severe corrosion, such as at depressions in the roof surface, areas around roof support sleeves, near roof
drains and vents, and similar locations where water can
accumulate. Badly corroded areas of the roof should be examined for evidence of leaks. The
condition of the paint on the roof will provide
a good indication of any
potential roof corrosion problem. Weathering
of the paint system is more
severe
on
the
exposure to sunlight and the presence of pools of
roof
due
to
its
water.
6.3.2 The underside of the roof should be checked for corrosion. Ultrasonic
thickness measurements should then be made to determine
the rate of corrosion.
The external face of the pontoon in the
region of the liquid level should
be inspected for grooving,
pitting, and corrosion because this area is prone to
corrosion due to the
liquid-vapor interface. 6.3.3 Floating roof UT reading shall be taken as a minimum as detailed below; (the spots required in check list can’t be substituted with the following requirement) Ultrasonic thickness measurements should be performed along the extension of the Vertical grid lines at 200mm from shell, at 2/3 radius and at 1/3 radius. In addition thickness measurement must be taken at locations where significant external and internal corrosion are observed. OR Rectangular plates- 6 readings per plate Sketch Plates-
3 readings per plate
10 additional readings between shell and gauge.
6.4
Determining the Tank Settlement
Shell and bottom settlement must be evaluated as part of the inspection
tank
activity to determine if any corrective action is required.
6.4 After completion of the full inspection, request any other needs for cleaning
or removal and cleaning of internals for detail inspection and
repairs or renewal if any.
6.5 Follow up the recommendations and the related repairs per standards, the
codes, ASME and API. Carry out the final inspection on completion
of the repairs and cleaning as applicable.
6.6 Applicable standards and codes: ASME SEC VIII D1, API STD 650, and
API STD 653.
