Order slotted and plain casing only from the approved well-section schedule. The designer should state screen type, aperture, pattern, open area, material, intervals, transitions, blank lengths, and any filter pack from the bore log and test data; formation labels do not create universal rules.
What does slotted casing do in a borewell?
Slotted casing provides openings specified by the well design; plain casing has no production openings. Their placement and performance depend on the complete screen, formation, annular-work, development, and operating design, so neither name guarantees sediment exclusion or sealing.
Slotted casing is also called perforated casing, screen casing, or simply "slots". The slots are machine-cut openings in the pipe wall that allow groundwater to pass into the borewell while the solid pipe maintains structural strength. Unlike wire-wound screens used in some municipal wells, slotted casing is a single steel pipe with laser-cut or plasma-cut openings. The slot width, length, spacing, and open-area percentage together control how much water enters and what particle size is admitted.
Different screen constructions have different geometry, strength, installation, inspection, cleaning, and rehabilitation considerations. The responsible designer should select and document the construction; this page does not promise a maintenance method or intervention-free service life.
Plan placement from the approved well section. The bore log and test data inform the designer, who must state screen and blank intervals, transitions, seals, sump, centralizers, and annular materials. Procurement should reproduce that schedule without extending or reducing it by a generic overlap rule.
How is slot geometry selected for different aquifer types?
Copy aperture, length, pattern, open area, tolerance, and acceptance method from the approved screen design. Grain-size and hydraulic data may inform that design, but no D50 ratio, formation label, or target yield on this page selects a slot geometry.
Slot geometry has three main parameters: slot width (the narrowest opening dimension), slot length, and open-area percentage (total slot opening area as a fraction of pipe surface). The slot width is selected to exclude the majority of formation particles — too wide and sand enters the pump; too narrow and water entry is restricted, causing turbulence, sand agitation, and reduced yield.
Copy slot width, length, pattern, and open-area from the approved bore design and grain-size data. Do not treat D₅₀, D₈₅, 0.5 mm / 3%, 1.0 mm / 5%, or 2.0 mm / 8% as universal IS 4270 prescriptions. Those figures are only illustrations of how designers talk about slots; the drawing and the invoked edition control the order.
If the approved design names continuous-spiral or bridge-slotted casing, copy that open-area and pattern onto the RFQ. Do not treat 12–18% open area as an IS 4270 manufacturing tolerance or as a CGWB prescription. Confirm the offered slot geometry on the written quotation.
RFQ field | Value to copy | Evidence | Acceptance
Screen construction | As approved | Design drawing and invoked standard | Project inspection plan
Aperture and tolerance | As approved | Screen schedule | Named measurement method
Pattern and open area | As approved | Hydraulic and structural design | Approved calculation and inspection
Intervals and transitions | As approved | Bore log and well section | Site record
Open area interacts with aperture, pattern, structural capacity, screen length, formation, pack, and operating conditions. The designer should document the hydraulic and structural basis; procurement should not increase or reduce open area from a general rule.
When is a gravel pack needed with slotted casing?
Use a filter pack only when the approved well design specifies it. The designer should state material, grading, placement interval, annular dimensions, volume, placement method, and acceptance using project data; this page does not prescribe a 2–8 mm band or formation rule.
A designed filter-pack system coordinates formation data, screen aperture, pack grading, annular geometry, placement, development, and acceptance. Procurement should copy those requirements and should not widen slots or change grading to pursue a generic inflow claim.
Where a filter pack is specified, quote it as a distinct designed item with source, cleanliness, grading, quantity, placement, and inspection requirements. Where it is not specified, return the question to the responsible designer rather than infer that the natural formation will filter adequately.
Gravel-pack size is a well-design decision. Copy the pack grading from the approved construction note. Do not treat a 4–6 times slot-width ratio, or the millimetre bands on this page, as a universal packing rule.
What does IS 4270 require for slotted casing?
Use the invoked IS 4270 edition for its applicable manufacturing requirements, and copy slot geometry, screen interval, transitions, and any overlap from the approved well design. This page does not prescribe screen placement or overlap.
Cite the IS 4270 edition named on the tender or consultant specification. This site also uses the 2001 edition elsewhere, so do not pick a year from a supplier page. Copy slot width, length, pattern, and any tolerance from the approved design and the invoked edition rather than from a ±0.05 mm or ±1.0 mm figure on this page.
Do not derive screen length or overlap directly from a formation label or initial log. Copy the approved interval and any transition allowance onto the RFQ; if it is missing, return the schedule to the responsible designer.
Do not change screen length to meet a cost target without design approval. The responsible designer should evaluate the hydraulic and structural consequences and issue a revised schedule; procurement should not predict sand lock, seasonal behaviour, or a universal full-aquifer-plus-overlap rule.
Where should plain casing be used instead of slotted?
Use plain casing only at the intervals shown on the approved well section. The designer should coordinate surface protection, seals, unstable or non-producing strata, screen transitions, sump, material, joints, and local groundwater requirements.
The approved well section should assign blank casing, screen, conductor or surface protection, seals, sump, and transitions for the project. Procurement should not infer a top, bottom, overlap, formation, or contamination-control interval from a generic borewell description.
Copy the conductor, surface protection, and sanitary-seal details from the approved construction note. Do not use “always plain,” a fixed first-few-metres rule, or a fixed offset below a water level as a substitute for the project design.
The approved design should state any lower blank section, sump, end closure, and transition connection. Confirm the offered components and markings on the written quotation rather than assuming a factory-welded collar or threaded coupling.
How do I specify slotted vs plain casing in an RFQ?
Copy each approved blank and screen interval, aperture, pattern, open area, transition, connection, sump, and filter-pack requirement as separate RFQ fields. Include separate line items without inventing an overlap or placement rule.
A clear RFQ separates plain and screen requirements by function and design interval. Use placeholders such as “screen aperture as drawing,” “open area as approved calculation,” and “metres as well section” until the responsible designer supplies final values.
If grain-size or other design data is missing, return the question to the responsible designer. Do not ask a fabricator to choose aperture from a formation label or insert a default open-area percentage.
State ordered connections, protectors, packing, handling, inspection, and acceptance explicitly. Ask the Kanpur quotation to confirm the exact plain and screen items offered; do not imply a standard packing method, availability, or outcome.