In this article, we will learn about the Ring Type Joint (RTJ) Gasket – Basics and Types. To read about Spiral Wound Gaskets click HERE
What is Ring Type Joint (RTJ) gasket?
The Ring Type Joint (RTJ) gasket is a forged ring that fits into the machined groove of an RTJ flange. The ring-type joint gaskets are either octagonal or oval in cross-section. RTJ gaskets are generally used for high pressure and high-temperature applications. It’s widely used in refinery, petrochemical and oil field drilling industries. The Ring type joints are manufactured as per ASME B16.20. They are dimensionally suitable for use with flanges manufactured as per standards ASME B 16.5, ASME B16.47, and API 6A.
Sealing Principle of a Ring Type Joint gasket
The axial compressive load (due to bolt tightening) act on the Ring type joint(RTJ) gasket causing them to deform and flow into irregularities of flange grooves. Due to this, metal-to-metal contact has formed between the gasket and flange that makes a seal.
The ring-type joints have an excellent tightness and tolerance to temperature and pressure changes. While installing a ring-type joint gasket very close attention must be given to their bolting up for uniform load acting on the gasket. Also, make sure the RTJ gasket and groove faces must be free of imperfections and debris.
Type of Ring Type Joints Gasket
There are three types of RTJ gaskets. They are
- R Type
- RX Type
- BX Type
R Type
This is the basic type of RTJ gasket and widely used in petrochemical industries. They are classified as two types base on the cross-section. They are
- Oval
- Octagonal
The original design of the R type gasket is Oval. The octagonal RTJ is a modification to the oval design and provides better sealing. R type rings are used for the flange rating from Class 150 to 2500. The surface finish of the gasket shall not be rougher than 63µ inches.
When compare with oval type gaskets, the octagonal type gaskets are widely used because of high sealing efficiency.
RX Type
RX type gaskets are fit into the same groove sizes of R type gaskets for interchangeability. The RX type gasket is wider than the R type gasket. Hence the flange face-to-face separation will be higher when compared with the R type gasket. RX type gaskets are normally specified up to Class 5000 flanges. The surface finish of the gasket shall not be rougher than 63µ inches. The asymmetric cross-section makes the gasket self-energising.
This type of gasket is widely used for the application were more effective sealing required and also resist vibrations, shock loadings, etc.,
BX Type
BX type gaskets are only suitable for API 6 BX type flanges. These gaskets are used for the Class rating of 2000 to 20000 psi. The BX type gasket has a pressure passage hole for pressure equalization on each sealing face sides. The surface finish of the gasket shall not be rougher than 32µ inches.
Type BX gaskets are not interchangeable with R or RX gaskets. The groove on a flange which accommodates a BX gasket is dimensionally different to that for R and RX gaskets
The pitch diameter of the ring is slightly greater than the pitch diameter of the flange groove. This preloads the gasket and creates a pressure energized seal. It is particularly important to check the flange face-to-face separation which must be uniform around the entire circumference of the flange.
Identification of RTJ Gasket
The outer surface of each RTJ gasket shall carry the manufacturer’s name or identification trademark. The gasket number prefixed by the letters R, RX, or BX followed by the gasket material identification. Refer below table for Material identified as shown in Table.
Example of RTJ Gasket Code
Type: Whether R, RX or BX. If R, state whether octagonal or oval. The type of ring selection based on Pipeline pressure and temperature.
Ring Number: For example, R11 will fit a 1/2 inch NB with the Class rating of 300-600 RTJ flang
Material: A variety of materials is available. MOC of RTJ gasket selected based on the fluid property. Refer below table for the material grade. For example identification code D is for Soft Iron.
Standard: Either ANSI B16.20 or API 6A. These two standards are equivalent and interchangeable.
Identification Table
| GASKET MATERIALS | BRINELL HARDNESS NUMBER (max) | ROCKWELL B SCALE
(max) |
TEMPERATURE LIMIT
oC |
IDENTIFICATION |
| Soft iron | 90 | 56 | -60 to +400 | D |
| Low carbon steel | 120 | 68 | -40 to +500 | S |
| 4-6% Chrome 1/2% molybdenum | 130 | 72 | -125 to +500 | F5 |
| 410 Stainless Steel | 170 | 86 | -20 to +500 | S410 |
| 304 Stainless Steel | 160 | 83 | -250 to +650 | S304 |
| 316 Stainless Steel | 160 | 83 | -196 to +800 | S316 |
| 347 Stainless Steel | 160 | 83 | -250 to +870 | S347 |
Advantages
- Ring Type Joints used for sealing high pressure up to 20,000 psi.
- RTJ Gaskets can be produced from a variety of material to suit the process application and flange grade.
- RTJ’s are an extremely reliable and robust sealing.
Disadvantages
- The ring-type gaskets are unfit for reuse due to the plastic flow of the ring joint in the flange faces to creating the seal.
- It’s very expensive when compared to other types of gaskets.
- For proper installation skilled labours required.