A pipe flanges package is rarely just a list of discs. On a real project it carries the service environment in every line: seawater on a ship side, hydrotreated sour gas in a refinery hydrocracker, condensate cycling through a power plant, firewater on a process skid. Get the specification right and the bolted joint runs for decades. Get it wrong and the same joint can cost weeks of downtime before the plant even reaches commissioning.

This walkthrough is built around the way we, as a full-cycle industrial piping manufacturer, see flange packages being scoped, ordered and inspected in the field. The intent is practical: help a project buyer move from a one-line "supply flanges" request to a specification that is actually buildable, inspectable and traceable — while keeping the entire pipe flanges package aligned with the connected piping, fittings and gaskets in the same shipment.

1. Start with the service environment, not the standard

A flange specification written as "ASME B16.5, Class 150, RF, A105" is technically complete but practically empty. The first filter should always be the service environment, because that single decision drives material, facing, rating and inspection level all at once.

• Seawater and marine cooling: Copper-nickel flanges (90/10 or 70/30) and ASME B16.5 Class 150/300 raised face are the common pairing. Our copper nickel flanges range is matched to EEMUA 234 and ASTM B466 for shipbuilding and offshore service.
• Refinery and hydrocracker: A182 F11/F22/F304/F316 on Class 300/600/900 raised face, with spiral-wound gaskets and certified stud bolt sets.
• Power plant and boiler: A182 F11/F22 high-temperature flanges, often RTJ facing for higher pressures, paired with alloy heat efficiency tubes on the connected exchanger side.
• Petrochemical process: Stainless or alloy flanges sized to the operating temperature and corrosion allowance, with full MTC traceability.

2. Match the flange material to the connected pipe

Material mismatch is one of the most common causes of field failure we see. The flange material must be metallurgically compatible with the pipe, the fittings and the gasket on both sides. For buyers sourcing everything from one supplier, this is a packaging question, not a metallurgical one. For buyers splitting the scope, it is a coordination question that needs a written record.

3. Specify the bolted joint as one system

A flange is half a joint. The other half is the gasket, the stud bolt and the nut. Too many RFQs list the flange with the right material and rating, but specify the stud bolt as "to suit" — and the wrong stud bolt grade is a frequent cause of through-bolt failures and torque loss in thermal cycling. The three items should be ordered, inspected and shipped together.

A typical Class 150 raised face joint on A105 flanges uses a non-asbestos compressed fiber gasket with ASTM A193 B7 stud bolts and ASTM A194 2H heavy hex nuts. The same joint in a Class 300 sour service needs a spiral-wound gasket with B7M/2HM bolting. The same joint in stainless with low chloride risk can use a flexible graphite gasket with B8/B8M stud bolts. The combination is not optional — it is what keeps the joint tight.

When we package a flange scope for an EPC, we bundle the pipe flanges, pipe fittings, gasket stud bolt nut sets and any industrial valves on the same heat number and dispatch them on a single packing list. That removes the chance of an A105 flange arriving with a B7 bolt from a different mill, and it gives the receiving inspector one traceability chain to check instead of three.

4. Pressure class is not a guess — it is a calculation

The pressure class on the flange drawing should match the maximum allowable working pressure at the design temperature, with a margin agreed with the project piping class. Class 150 at 200°C is a different joint than Class 150 at 400°C. Higher temperatures reduce the allowable pressure on carbon steel flanges faster than buyers expect. If the service temperature is high, the same nominal pressure class in alloy steel is usually a safer and more compact joint than a heavier carbon steel class.

For buyers who do not want to recalculate rating charts for every line, the practical shortcut is to align flange class with the connected piping class. If the line is ASME B31.3 Class 150 at 300°C, the flange is the same class. If the line moves to a higher class for any reason, the flange moves with it.

5. Facing, gasket and finish — three things that travel together

Raised face (RF) is the default for most process piping. Flat face (FF) is used where the connected component is cast iron or a flat-face valve. Ring-type joint (RTJ) is reserved for high-pressure hydrocarbon service where spiral-wound gaskets are not acceptable. Tongue-and-groove and male/female are niche facings that should only be specified if the project really needs them — the cost of getting them reversed on site is far higher than the cost of staying on RF.

The surface finish matters more than many specs admit. ASME B16.5 describes a specific serrated finish (typically 125–250 micro-inches Ra) on the raised face. This finish is what gives the spiral-wound or compressed fiber gasket the friction it needs to bite. A flange that has been machined too smooth will leak even with the correct gasket. A flange that has been machined too rough will not seat the gasket evenly. We hold the serration pattern within the standard range and check it on the mill test report.

6. Documentation that the receiving inspector will actually check

The certificate of inspection is the most inspected document in any piping package. For a flange shipment, the minimum that should accompany every pallet is:

• Mill Test Certificate (MTC) per EN 10204 3.1, with the heat number, chemical composition and mechanical results matching the marking on the flange.
• Dimensional report against the standard cited (ASME B16.5, EN 1092-1, GOST, JIS).
• Pressure test or visual & dimensional report if the project requires 100% inspection rather than sampling.
• Coating and packaging record, including the desiccant, wrapping and crating if the destination is humid or sea-freight.
• Cross-reference with the connected pipe fittings and the gasket stud bolt nut pack on the same shipment.

When the package is consolidated, this is a single document set per pallet. When the package is split across suppliers, it is a coordination job that falls back to the EPC — and that is where the most delays and rejections actually happen.

Common procurement mistakes we see — and how to avoid them

Three patterns come up on almost every project we review. They are not exotic; they are routine, and they are easy to fix once the team sees them.

• Specifying the flange before the line class is final. The first revision of a piping class is rarely the last. Holding flange orders until the line class is frozen avoids significant rework in the flange list — in our experience, the rework load on a flange list is usually much higher than on the pipe or fittings, because flange counts multiply at every branch connection and valve connection in the line.
• Mixing standards across the same joint. A weld neck flange to ASME B16.5 will not match a backing ring to DIN 2642 on the same flange bolt circle. The standard must be one and the same from flange to gasket to bolt.
• Forgetting the valve end connection. The industrial valves in the line must match the flange facing. A raised-face valve needs a raised-face flange. A flat-face valve (common on butterfly or lug valves) needs a flat-face flange. Mixing them forces a spacer ring in the field.

Why a full-cycle supplier matters for the flange package

The reason this guide is written around the entire package — pipe, fittings, flanges, gaskets, bolts and valves — is that a flange never arrives on site alone. It is one line item in a piping class, and that piping class sits inside a piping package, and that package sits inside an EPC or a refinery turnaround.

EZ STEEL INDUSTRIAL was founded in 1994 in Hunan, China, and has been a full-cycle industrial piping manufacturer for more than three decades. The eight product lines — carbon & alloy steel, stainless steel, copper-nickel alloy, heat efficiency tubes, pipe fittings, pipe flanges, gasket-stud-bolt-nut, and industrial valves — are produced in-house, certified to API / EN / ASME standards and shipped from a single dispatch chain. For a buyer, that means one PO, one packing list, one set of MTCs and one contact for any claim.

Annual capacity of 480,000+ units and 500+ staff, combined with API 5L, ASME and ISO 9001 certifications, allows the flange package to be matched against the connected stainless steel pipe or carbon steel pipe on the same heat number, and against the heat efficiency tubes on the connected exchanger, all without leaving the supplier.