Technical knowledge
Flange leak troubleshooting: a checklist that finds the real cause
A structured approach to diagnosing leaking alloy flanges: separating bolting, gasket, facing, alignment and material causes, with the checks to make before you blame the alloy.
The order that saves time
- Confirm the design. Pressure, temperature, fluid, gasket type and class. Many leaks are the result of a substitution made during construction.
- Inspect the gasket. Look for blow out, creep, crushing, chemical attack and whether the correct gasket was fitted.
- Inspect the faces. Look for scoring, corrosion, embedded debris, distortion and the correct finish.
- Check the bolting. Corrosion, elongation, galling, incorrect grade, lack of lubrication, uneven preload.
- Check alignment. Pipe strain, flange rotation, inadequate support, thermal growth.
- Check the material. Verify with positive material identification and the certificate.
Symptoms and their usual causes
| Observation | Likely cause | Corrective action |
|---|---|---|
| Leak starts after a thermal cycle | Bolt relaxation and gasket creep | Re-torque, review gasket and bolting selection |
| Leak at one point around the flange | Uneven bolt load or misalignment | Cross pattern tightening, correct alignment |
| Gasket extruded into the bore | Over compression or wrong gasket | Correct gasket type and compression |
| Corrosion around bolt holes | Galvanic or crevice attack | Isolation, material review |
| Sealing face pitted under the gasket | Crevice corrosion | Higher alloy, gasket and geometry review |
| Leak after a pressure surge | Loss of preload or inadequate support | Review supports, surge protection |
Assembly basics that prevent most leaks
- Clean and inspect both faces before fitting the gasket.
- Use the correct lubricant and apply it to threads and nut faces.
- Tighten in a cross pattern in several stages to the specified torque.
- Do not reuse gaskets or ring joints.
- Plan a re-torque after the first thermal cycle.
- Record the torque values so future comparisons are meaningful.
Questions about this topic
Should I upgrade the alloy after a leak?
Only after the mechanical causes have been ruled out. Bolting, gasket, alignment and assembly problems account for the majority of leaks, and an alloy upgrade will not fix any of them.
How often should alloy joints be re-torqued?
Plan a re-torque after the first thermal cycle and at the first scheduled shutdown. Check the project specification, since some services require defined intervals.
Can a leaking ring type joint be fixed by extra bolt load?
Usually not. If the ring or the groove is damaged, both must be assessed. Rings should never be reused, and a damaged groove needs machining assessment before the joint is remade.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email demi@nickel-alloy.com or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
Talk to an engineer
Share your duty conditions and we will shortlist candidate alloys within one working day.