Carbon Steel Slip-On Flanges

Carbon Steel Slip-On Flanges

Specifications

Materials	ASTM A105 (carbon steel)
Standards	ASME B16.5 (1/2 inch to 24 inch), ASME B16.47 Series A and Series B (26 inch to 60 inch)
Size Range	NPS 1/2 inch to 60 inch
Pressure Class	Class 150, Class 300, Class 600 (per ASME B16.5 / B16.47). For higher pressure classes, weld neck flanges are recommended.
Flange Face Type	RF (Raised Face) — standard; FF (Flat Face) — on request for low-pressure cast iron or non-metallic pipe connections
Surface Treatment	Rust preventive oil + VCI film (standard for sea shipping); hot-dip galvanizing per ASTM A153; cold blackening; clear lacquer
Manufacturing Process	Forged
MOQ	Negotiable based on specifications and destination port. Standard items can ship from a single pallet; custom orders typically require full container load.
Lead Time	Standard items ship within 7-15 days; custom orders 20-30 days; shipping time additional depending on destination (typically 30-60 days sea voyage to Middle East ports)
HS Code	7307.91 (carbon steel flanges); GCC Common External Tariff 5% on CIF value for Oman and UAE import
Customization	Non-standard sizes, special bore diameters, modified thicknesses, and unique flange configurations are supported. Technical drawings or detailed specifications required for custom orders.
Documents	EN 10204 Type 3.1 MTC (standard with every shipment); additional test reports (impact, hardness, NDT) on request at quotation stage

Samples, Third-Party Inspection and Test Records

Sample pieces can be produced before the batch runs, so that dimensions, bevel profile and fit-up can be checked on your side first. Sample cost and delivery time are advised with the quotation, based on size and material.

Buyer-nominated inspection is supported. SGS, BV, Intertek or your own inspector can witness dimensional checking, marking, coating and container loading at the production site, and we provide the documents and site access needed for the visit. Where a visit is not practical, the same checks can be followed through a live video walkthrough. Third-party inspection fees are normally carried by the buyer.

Non-destructive testing and hydrostatic test records are available on request and can be shipped with the order, together with the EN 10204 3.1 material certificate, the heat number and marking list, dimensional records, packing list and certificate of origin. Tell us at enquiry stage which records your project requires, and they are included in the quotation.

Slip-On vs Weld Neck

Criterion	Slip-On (SO)	Weld Neck (WN)
Pressure Class Range	Class 150 - Class 600	Class 150 - Class 2500
Temperature Limit	Up to ~200°C (depends on material)	Up to ~600°C+ (depends on material)
Weld Type	Single fillet weld (inside + outside of hub)	Butt weld (full penetration, double-sided)
Weld Strength	Lower (stress concentration at pipe end)	Higher (stress distributed through tapered hub)
Cyclic Service	Not recommended	Recommended
Sour Service (NACE)	Not recommended	Recommended (with proper material selection)
Cost (relative)	60-75% of WN price	100% (baseline)
Installation Time	Faster (simple fillet weld, no RT required)	Slower (butt weld + RT typically required)
Size Range	NPS 1/2" to 60"	NPS 1/2" to 60"
Typical Applications	Water, HVAC, low-pressure utility, chemical plant	Oil & gas, refinery, power plant, high-pressure
non-critical lines	steam, desalination RO

Selection Logic

Buyer FAQ

Q1: Slip-On vs Weld Neck — how to choose? Which is more suitable for water treatment plants?

A1: For water treatment and sewage treatment applications, the choice depends on pressure and service conditions. Low-pressure service (Class 150, ≤ 80°C, non-cyclic) — slip-on flanges are sufficient and more cost-effective. Medium-pressure service (Class 300, with pressure cycling during pump start-up/shut-down) — weld neck flanges are recommended. High-pressure RO systems in desalination plants (Class 600+) — weld neck flanges are mandatory. The selection logic is: SO for non-critical low-pressure lines; WN for any high-pressure, cyclic, or critical service.

Q2: Can slip-on flanges be used in petrochemical pipelines?

A2: Yes, slip-on flanges can be used in petrochemical applications, but only for low-to-medium pressure utility and non-critical process lines (typically Class 150-300, non-cyclic, non-corrosive service). For main process lines, high-pressure service, corrosive media, or cyclic service — weld neck flanges are required. Please specify your exact service conditions (pressure, temperature, fluid type, cyclic vs static) at quotation stage, and we will recommend the appropriate flange type for your application.

Q3: What is the maximum pressure class for slip-on flanges?

A3: Per ASME B16.5, slip-on flanges are standardly rated up to Class 600. For pressure classes above Class 600, weld neck flanges are recommended due to the higher stress concentration at the slip-on fillet weld. If your project requires slip-on flanges above Class 600 for special reasons (e.g., alignment tolerance in field assembly), please contact us — feasibility assessment is provided before quotation.

Q4: What is the maximum service temperature for slip-on flanges?

A4: Carbon steel slip-on flanges (ASTM A105) are typically rated for service temperatures up to ~200°C, depending on the pressure class. For service above this range, an alternative material grade is required — please share your operating temperature and we will confirm the suitable material. For high-temperature service — particularly cyclic thermal service — weld neck flanges are recommended.

Q5: Can slip-on flanges be used in seawater desalination plants?

A5: Yes, but the application area matters. In desalination plants, slip-on flanges are commonly used in the intake, pretreatment, and low-pressure pump station sections (typically Class 150-300). For high-pressure RO systems (Class 600+) and brine rejection sections — weld neck flanges are mandatory due to high pressure and pump-cycling service. Material selection: standard ASTM A105 for low-salinity and intake sections. For high-salinity or chloride-exposed sections, a material upgrade is required — please share your water chemistry and we will confirm the suitable grade.

Q6: Can slip-on flanges be used in HVAC systems?

A6: Yes, slip-on flanges are the standard choice for HVAC chilled water, condenser water, and hot water distribution systems. Typical service conditions (Class 150, ≤ 100°C, low pressure cycling) are well within slip-on flange ratings. For high-temperature steam systems in HVAC (e.g., high-pressure steam humidification), weld neck flanges may be preferred. Material selection: ASTM A105 is standard; hot-dip galvanized coating is commonly applied for corrosion protection in humid environments.

Q7: Can slip-on flanges be used in oil & gas gathering pipelines?

A7: Slip-on flanges are not recommended for oil & gas gathering and transmission pipelines. The combination of high pressure (typically Class 300-900), cyclic service, and safety-critical service conditions requires the higher weld integrity of weld neck flanges. Slip-on flanges may be acceptable only for low-pressure utility lines in oil & gas facilities (e.g., instrument air, utility water at Class 150). For main production lines, weld neck flanges are mandatory.

Q8: Is the weld strength of slip-on flanges sufficient? Are they more prone to leakage than weld neck flanges?

A8: Slip-on flange fillet welds provide adequate strength for low-to-medium pressure non-cyclic service, but they have higher stress concentration at the pipe end compared to the butt weld of weld neck flanges. In cyclic service (pressure or thermal cycling), the slip-on weld is more susceptible to fatigue cracking. For non-cyclic low-pressure service, slip-on flanges perform reliably with proper welding procedures (qualified per ASME Section IX). For cyclic or critical service, weld neck flanges are recommended.

Q9: What is the cost difference between slip-on and weld neck flanges? Is the price difference worth it?

A9: Slip-on flanges typically cost 60-75% of equivalent weld neck flanges (same size, pressure class, material). The price difference reflects the simpler manufacturing (no tapered hub machining) and faster installation (single fillet weld vs butt weld). For non-critical low-pressure service, the cost savings are significant and worth it. For high-pressure, cyclic, or critical service, the additional cost of weld neck flanges is justified by the higher weld integrity and longer service life. We can provide side-by-side quotations for both options at your request.

Q10: What is the HS Code and tariff for carbon steel slip-on flanges imported into Oman and the UAE?

A10: Carbon steel slip-on flanges are classified under HS Code 7307.91 (tube or pipe fittings of iron or steel — flanges of iron or steel, other than stainless). GCC Common External Tariff is 5% on CIF value for goods imported into Oman and the UAE. Standard import documentation includes Commercial Invoice, Packing List, Bill of Lading, Certificate of Origin (Form A or applicable FTA), MTC 3.1, and Fumigation Certificate for wooden packaging. Since 2026, electronic Bayan (e-Bayan) declaration is mandatory for Oman customs clearance; UAE importers file through Dubai Customs or the relevant emirate portal. We can provide full export documentation support per your request.

Q11: What sizes and pressure ratings are available for carbon steel slip-on flanges?

A11: NPS 1/2 inch to 60 inch. Class 150, Class 300 and Class 600 to ASME B16.5 and B16.47. Sizes and ratings outside this range can be reviewed against your drawing. The exact range confirmed for your order is stated in the quotation.

Q12: How is the wall thickness determined for carbon steel slip-on flanges?

A12: Flange dimensions, including hub and thickness, are fixed by the ASME standard for the size and pressure class you specify. They are not chosen separately. The matching pipe schedule is confirmed at quotation stage.

Q13: What is the lead time for carbon steel slip-on flanges?

A13: Standard sizes in regular material normally take 7-15 days. Non-standard sizes, special materials and custom orders take longer. The exact lead time for this product is given in the specification table on this page and is confirmed in writing with your quotation. Sea freight to the Gulf is additional and depends on the destination port. All lead times are subject to the production schedule at the time of order.

Q14: Is there a minimum order quantity for carbon steel slip-on flanges?

A14: There is no fixed minimum. Standard items can ship from a single pallet, and custom production is normally quoted at full container load. Small trial orders and mixed-size orders are accepted. Send your size list and we will confirm what can be combined in one shipment.

Q15: How are carbon steel slip-on flanges packed and marked?

A15: Flanges and fittings are packed in plywood cases or on plywood pallets with anti-rust treatment, strapped and stretch-wrapped for sea freight. Each piece carries the heat number, and the material, size, standard and pressure class or schedule are marked on the item or on the case label. Shipping marks are printed to your specification, and a fumigation certificate is provided where wooden packaging is used.

Q16: Can you produce carbon steel slip-on flanges to our drawing or to non-standard specifications?

A16: Yes. Send the drawing, material, quantity and the applicable standard, and we will confirm feasibility and quote. Non-standard angles, non-standard schedules, special materials and special dimensions are produced against your drawing. The details we need to quote are listed on our custom service page. The details we need to quote are listed on our custom service page.

Engineer's Note

The following technical guidance reflects the perspective of a senior piping engineer with extensive experience in industrial piping system design.

Slip-on flanges are a versatile and economical connection for many piping systems, but their use requires careful evaluation of service conditions. The following factors should drive your selection:

1. Service Pressure

• Class 150 and below: SO is suitable for virtually all non-cyclic service
• Class 300: SO is acceptable for non-cyclic service; WN recommended for cyclic service
• Class 600 and above: WN strongly recommended

2. Service Temperature

• Up to 200°C (carbon steel A105): SO suitable
• 200-400°C: Material upgrade required; SO acceptable for non-cyclic, WN recommended for cyclic
• Above 400°C: WN strongly recommended

3. Service Type (Static vs Cyclic)

• Static (constant pressure, constant temperature): SO is acceptable up to Class 600
• Cyclic (pressure cycling from pump start-up/shut-down, thermal cycling from process): WN recommended regardless of pressure class

4. Fluid Type

• Water, air, low-pressure steam: SO is standard
• Hydrocarbons (oil, gas): WN recommended
• Corrosive media: Material grade must be matched to the specific fluid — please share your media composition for confirmation; SO or WN based on pressure
• Sour service (H2S, per NACE MR0175): WN with NACE-compliant material

5. Inspection Requirements

• SO installations: Visual inspection of fillet weld typically sufficient
• WN installations: Butt weld often requires radiographic testing (RT) per ASME B31.3
• Consider inspection cost and time in your total project budget

6. Common Mistakes to Avoid

• Using SO for high-pressure steam lines: Fatigue failure risk
• Using SO for cyclic thermal service: Weld cracking risk
• Using SO for sour service without NACE compliance: Sulfide stress cracking (SSC) risk
• Using SO above Class 600: Not standard per ASME B16.5

For project-specific engineering support, please share your service conditions (pressure, temperature, fluid, cyclic vs static) and we will review the specification and provide a written recommendation.

Frequently Asked Questions

Slip-On vs Weld Neck — how to choose? Which is more suitable for water treatment plants?

For water treatment and sewage treatment applications, the choice depends on pressure and service conditions. Low-pressure service (Class 150, ≤ 80°C, non-cyclic) — slip-on flanges are sufficient and more cost-effective. Medium-pressure service (Class 300, with pressure cycling during pump start-up/shut-down) — weld neck flanges are recommended. High-pressure RO systems in desalination plants (Class 600+) — weld neck flanges are mandatory. The selection logic is: SO for non-critical low-pressure lines; WN for any high-pressure, cyclic, or critical service.

Can slip-on flanges be used in petrochemical pipelines?

Yes, slip-on flanges can be used in petrochemical applications, but only for low-to-medium pressure utility and non-critical process lines (typically Class 150-300, non-cyclic, non-corrosive service). For main process lines, high-pressure service, corrosive media, or cyclic service — weld neck flanges are required. Please specify your exact service conditions (pressure, temperature, fluid type, cyclic vs static) at quotation stage, and we will recommend the appropriate flange type for your application.

What is the maximum pressure class for slip-on flanges?

Per ASME B16.5, slip-on flanges are standardly rated up to Class 600. For pressure classes above Class 600, weld neck flanges are recommended due to the higher stress concentration at the slip-on fillet weld. If your project requires slip-on flanges above Class 600 for special reasons (e.g., alignment tolerance in field assembly), please contact us — feasibility assessment is provided before quotation.

What is the maximum service temperature for slip-on flanges?

Carbon steel slip-on flanges (ASTM A105) are typically rated for service temperatures up to ~200°C, depending on the pressure class. For service above this range, an alternative material grade is required — please share your operating temperature and we will confirm the suitable material. For high-temperature service — particularly cyclic thermal service — weld neck flanges are recommended.

Can slip-on flanges be used in seawater desalination plants?

Yes, but the application area matters. In desalination plants, slip-on flanges are commonly used in the intake, pretreatment, and low-pressure pump station sections (typically Class 150-300). For high-pressure RO systems (Class 600+) and brine rejection sections — weld neck flanges are mandatory due to high pressure and pump-cycling service. Material selection: standard ASTM A105 for low-salinity and intake sections. For high-salinity or chloride-exposed sections, a material upgrade is required — please share your water chemistry and we will confirm the suitable grade.

Can slip-on flanges be used in HVAC systems?

Yes, slip-on flanges are the standard choice for HVAC chilled water, condenser water, and hot water distribution systems. Typical service conditions (Class 150, ≤ 100°C, low pressure cycling) are well within slip-on flange ratings. For high-temperature steam systems in HVAC (e.g., high-pressure steam humidification), weld neck flanges may be preferred. Material selection: ASTM A105 is standard; hot-dip galvanized coating is commonly applied for corrosion protection in humid environments.

Can slip-on flanges be used in oil & gas gathering pipelines?

Slip-on flanges are not recommended for oil & gas gathering and transmission pipelines. The combination of high pressure (typically Class 300-900), cyclic service, and safety-critical service conditions requires the higher weld integrity of weld neck flanges. Slip-on flanges may be acceptable only for low-pressure utility lines in oil & gas facilities (e.g., instrument air, utility water at Class 150). For main production lines, weld neck flanges are mandatory.

Is the weld strength of slip-on flanges sufficient? Are they more prone to leakage than weld neck flanges?

Slip-on flange fillet welds provide adequate strength for low-to-medium pressure non-cyclic service, but they have higher stress concentration at the pipe end compared to the butt weld of weld neck flanges. In cyclic service (pressure or thermal cycling), the slip-on weld is more susceptible to fatigue cracking. For non-cyclic low-pressure service, slip-on flanges perform reliably with proper welding procedures (qualified per ASME Section IX). For cyclic or critical service, weld neck flanges are recommended.

What is the cost difference between slip-on and weld neck flanges? Is the price difference worth it?

Slip-on flanges typically cost 60-75% of equivalent weld neck flanges (same size, pressure class, material). The price difference reflects the simpler manufacturing (no tapered hub machining) and faster installation (single fillet weld vs butt weld). For non-critical low-pressure service, the cost savings are significant and worth it. For high-pressure, cyclic, or critical service, the additional cost of weld neck flanges is justified by the higher weld integrity and longer service life. We can provide side-by-side quotations for both options at your request.

What is the HS Code and tariff for carbon steel slip-on flanges imported into Oman and the UAE?

Carbon steel slip-on flanges are classified under HS Code 7307.91 (tube or pipe fittings of iron or steel — flanges of iron or steel, other than stainless). GCC Common External Tariff is 5% on CIF value for goods imported into Oman and the UAE. Standard import documentation includes Commercial Invoice, Packing List, Bill of Lading, Certificate of Origin (Form A or applicable FTA), MTC 3.1, and Fumigation Certificate for wooden packaging. Since 2026, electronic Bayan (e-Bayan) declaration is mandatory for Oman customs clearance; UAE importers file through Dubai Customs or the relevant emirate portal. We can provide full export documentation support per your request.

What sizes and pressure ratings are available for carbon steel slip-on flanges?

NPS 1/2 inch to 60 inch. Class 150, Class 300 and Class 600 to ASME B16.5 and B16.47. Sizes and ratings outside this range can be reviewed against your drawing. The exact range confirmed for your order is stated in the quotation.

How is the wall thickness determined for carbon steel slip-on flanges?

Flange dimensions, including hub and thickness, are fixed by the ASME standard for the size and pressure class you specify. They are not chosen separately. The matching pipe schedule is confirmed at quotation stage.

What is the lead time for carbon steel slip-on flanges?

Standard sizes in regular material normally take 7-15 days. Non-standard sizes, special materials and custom orders take longer. The exact lead time for this product is given in the specification table on this page and is confirmed in writing with your quotation. Sea freight to the Gulf is additional and depends on the destination port. All lead times are subject to the production schedule at the time of order.

Is there a minimum order quantity for carbon steel slip-on flanges?

There is no fixed minimum. Standard items can ship from a single pallet, and custom production is normally quoted at full container load. Small trial orders and mixed-size orders are accepted. Send your size list and we will confirm what can be combined in one shipment.

How are carbon steel slip-on flanges packed and marked?

Flanges and fittings are packed in plywood cases or on plywood pallets with anti-rust treatment, strapped and stretch-wrapped for sea freight. Each piece carries the heat number, and the material, size, standard and pressure class or schedule are marked on the item or on the case label. Shipping marks are printed to your specification, and a fumigation certificate is provided where wooden packaging is used.

Can you produce carbon steel slip-on flanges to our drawing or to non-standard specifications?

Yes. Send the drawing, material, quantity and the applicable standard, and we will confirm feasibility and quote. Non-standard angles, non-standard schedules, special materials and special dimensions are produced against your drawing. The details we need to quote are listed on our custom service page.

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• EN 10204 3.1 material certificate

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