What is a pipe flange?

A pipe flange is a mechanical component used to connect pipes, valves, pumps, and other equipment in a piping system. Flanges are bolted together with a gasket in between to create a pressure-tight seal, and they allow for easy assembly, disassembly, and maintenance of piping systems without cutting or welding.

What are the most common types of pipe flanges?

The most common pipe flange types are weld neck, slip-on, blind, socket weld, threaded, and lap joint flanges. Each type has specific advantages and is suited to different pressure, temperature, and installation requirements. Weld neck flanges are preferred for high-pressure applications while slip-on flanges are more economical for lower pressure service.

How do I select the right flange for my application?

Selecting the right flange requires considering several factors including pipe size, operating pressure and temperature, fluid type, applicable industry codes, and installation requirements. Key decisions include flange type, pressure class, material grade, and face type. Texas Flange's team can assist with flange selection for any industrial application.

What is the difference between ANSI and ASME flanges?

ANSI and ASME flanges refer to the same dimensional standards — ASME B16.5 was formerly known as ANSI B16.5. The terms are often used interchangeably in the industry. Both refer to flanges manufactured to the same dimensional and pressure rating standards covering sizes NPS 1/2 through NPS 24.

How are flanges measured and sized?

Flanges are sized by nominal pipe size (NPS), which refers to the approximate inside diameter of the pipe they connect to rather than the actual flange dimensions. A 4-inch flange for example connects to 4-inch nominal pipe. Flange dimensions including outside diameter, bolt circle, and thickness vary by both pipe size and pressure class.

Flange FAQs

Flange FAQs (Frequently Asked Questions)

How Do I Inquire About A Flange?

For clarity and ease of understanding, Texas Flange suggests you describe your part in this order: Quantity, Size (nominal pipe size), Pressure Class (150-2500), Facing (RF, FF, RTJ, ect.), Type (WN, SO, Threaded, Blind, SW, LJ), Bore (if SW or WN), Material.

So for example: 2EA 4” 300# RFWN STD 304

Do You Sell Reducing Flanges?

If so, why can’t I find dimensions for them?

Yes, we sell reducing flanges (WN, SW, SO, Thrd) with the hubs or made from blinds (in the cases of SO or Thrd). B16.5 gives rules for how we do the reductions, but to my knowledge nobody produces the cut sheets. If you consider the various combinations possible it would get quite lengthy.

For reducing flanges with hubs, all dimensions except the Length Thru Hub (or OAL) come straight from the regular flange dimensions.

From the larger size:

OD, Thk, Bolt pattern, RF Dia

From the smaller size:

OD at base of hub

OD at point of weld

IF (dependent on schedule)

Hub height

Using abbreviations found in the catalog, here’s how you can calculate the OAL for a reducing weldneck:

Hub height = L2 – thk [all dims per smaller size]

LTH = Hub height + thk(of larger size) + face height

As an example, for a 4” x 3” 600# RF Red WN XH, one would calculate the LTH as follows: Hub height = 3.25 – 1.25 = 2.00” LTH – 2.00 + 1.50 + 0.25 = 3.75”

How Do I Order A Slip On Flange Above 24”?

That depends entirely on what you are trying to accomplish. If you want a part that is automatically covered under ASME Code, then forget Slip Ons and opt for a Weld Neck from B16.47 Series A or B. If you don’t need to meet code or can run the calculations for your application, then the options open up:

For the Standard 150# drilling we offer the “Class 125/ 150#” series. These are made per B16.1 which is a Cast Iron Spec. We make them most often in Carbon Steel per A105. In addition, we offer them in Stainless 304, 316, and all the other alloys too. Since the spec is for Cast Iron and the applications in industry usually call for another material these are made “per B16.1 Dimensions only.” There is also a much less commonly used Class 250 option available.

There are also 150#, 300#, 400#, 600#, and 900# Slip Ons that were designed by Tube Turns to match the MSS-SP-44 spec (which was almost 100% brought into ANSI B16.47 under Series A.) These were originally designed to meet ASME Code of the time, but quite some time has passed since then and as a result in many cases they do not meet current design criteria. Nevertheless, they are used on a frequent enough basis that we stock the contoured forgings in A105 and do a decent amount of business getting rolled rings to make them in other materials.

We have also been asked to make Slip Ons to match the B16.47 Series B dimensions. For this there is an agreed upon industry standard method that provides no calculations but has garnered wide acceptance. The basic design includes cutting down the weld neck forging and opening the ID.

Still more options remain as Taylor Forge designed many “Boiler Code” flanges that serve to add Slip On options in various classes. These parts are drilled per their design and do not match any other standard. The classes offered are 75, 175, and 350. For the dated information on pressure-temperature allowance see Taylor Forge Catalog 541 or contact us.

Finally, the American Waterworks Association (AWWA) under their spec C207 has designs on a series of plate Slip-on flanges in Class B, D, E, and F. They also have hubbed Slip Ons in Class D and E.

What’s The Difference Between Series A And Series B Flanges?

The short answer is Series A tend to be larger, heavier, have fewer bolt holes, and costs more.

The longer answer is that these were competing specifications that were brought together in B16.47 as is put forth in a note from our catalog: ASME has incorporated most of the MSS-SP44 specification into B16.47 Series A and most of the API 605 Specification into B16.47 series B.

They have also added Blinds to these two specs.

You may note that these specs only include Weld Necks and Blinds. For Slip Ons over 24” you must refer to either Industry Standard (which are not automatically covered by ASME) or Boiler Code Flanges.

If you need help deciding which flange best suits your application, feel free to contact us.

Do You Provide Expedited Service? What Does It Cost?

We have a joke around the office about the fellow who calls up and asks how much a flange costs. “Depends, which one of the 82 million different configurations do you need?”

We do offer expedited service but giving any kind of rule of thumb on cost is hard to do. It really comes down to what material is needed and which processes must be interrupted or ran in overtime.

Suffice to say, we will always try to appreciate and understand our customers’ needs and can usually turn parts out in a much quicker manner than “standard lead time” if you truly need it.

The one caveat to this is if it takes 5 hours to machine the part, then the quickest we will ever be able to quote is 5 hours. With that in mind, please feel free to ask for the impossible and we’ll quote what we can.

Why Doesn’t Your Catalog Show API Dimensions?

What’s The Difference Between Sch40, True 40, And Sch40S In Larger Sizes?

The industry standard is to specify “TRUE 40” to distinguish Sch40 bores from Std bores for 12” NPS and larger when the application calls for the heavier wall.

The industry standard is to specify “TRUE 80” to distinguish Sch80 bores from XH bores for 10” NPS and larger when the application calls for the heavier wall.

Normally, when “Sch80” and “Sch40” are used without any other qualifier such as wall thickness or ID, XH and Std bores (respectively) will be supplied.

When Sch40 or 80 are specified followed by a “S” they are automatically assumed to refer to Std and XH respectively.

What Type Of Carbon Steel Should I Specify For AWWA Flanges?

AWWA C207 specifies parameters for the carbon steel. The criteria given allows for A283, A36, A516-70, A105, and A181-60 to be used.

Limiting your spec to any singular variant of those materials can double or triple your costs.

So for general purposes we recommend leaving the material callout for AWWA carbon steel flanges as “Carbon Steel per AWWA.”

You will get a part that meets the design criteria set forth in AWWA and you won’t pay a premium for a “preferred” material.

What Is A DSA?