technical report gaskets for polyethylene pe pipe connections

Technical report Gaskets for polyethylene (PE) pipe connections

A technical paper presented by

James Walker Australia Pty Ltd

Abstract: A technical guide for gaskets to suit PE pipe connections

Disclaimer: This information is based on our general experience, but because of factors which are outside our knowledge and control, no warranty is given or is to be implied with respect to such information. If any doubt exists, please seek advice from James Walker.

Gaskets for PE pipe connections

Table of Contents

1.0 REFERENCES AND STANDARDS ................................................................................................ 2

2.0 PURPOSE ....................................................................................................................................... 3

3.0 INTRODUCTION ............................................................................................................................. 3

4.0 SCOPE ............................................................................................................................................ 3

5.0 PE PIPE CLASSIFICATIONS ......................................................................................................... 4

6.0 PE FLANGE CONNECTIONS ......................................................................................................... 4

7.0 METAL BACKING RINGS ............................................................................................................... 5

8.0 GASKET TYPES, STYLES ............................................................................................................. 7

9.0 GASKET MATERIAL SELECTION ................................................................................................. 8

10.0 GASKET DIMENSIONS .................................................................................................................. 9

10.1 Gasket inside diameter ..................................................................................................... 10 10.2 Gasket thickness .............................................................................................................. 11

11.0 BOLT LOAD/TORQUE VALUES ................................................................................................... 11

12.0 HOW TO ORDER GASKETS ........................................................................................................ 13

Index of Figures

Figure 1- PE stub flange to PE stub flange ............................................................................................................. 4

Figure 2- PE stub flange to Metal flange ................................................................................................................. 5

Figure 3-PE stub flange to metal flange (flat or raised face) ................................................................................... 5

Technical report – Gaskets for PE pipe connections v3(Released)

James Walker TR14-08 – v3(Released) Page 2 of 14 Updated: 03-MAR-2015

Document Control

Rev Revision date

Summary of Changes Changes marked

0.1 14-AUG-14 Initial draft

0.2 18-AUG-14 Updated after internal review by JWA

1.0 01-SEP-14 Released following general technical review. References to ePTFE material removed. Material selection for potable water updated

2.0 10-FEB-15 Revised per comments received from PL&PS review team.

3.0 03-MAR-15 Added notes to disadvantages for drop-in gaskets (Fig 5 and Table 6)

Glossary A list of terms, abbreviations and acronyms used within the document.

Abbreviation Definition

ESA European Sealing Association

FSA Fluid Sealing Association

HDPE High density Polyethylene

PE Polyethylene

1.0 References and Standards

The following related documents and standards are referenced in this document.

Reference document Title Issue Date(3)

POP007(1) METAL BACKING FLANGES FOR USE WITH POLYETHYLENE (PE) PIPE FLANGE ADAPTORS

01-MAR-2006

TN-38(2) Bolt Torque For Polyethylene Flanged Joints JULY-2011

AS/NZS 4130 Polyethylene (PE) pipes for pressure applications 2009

AS ISO 9624 Polyethylene (PE) pipe for fluids under pressure – mating dimensions of flange adaptors and loose backing flanges

2008

ASME B16.5 Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard

2013

ASME B16.21 Non-metallic flat gaskets for pipe flanges 2011

ASME PCC-1 Guidelines for Pressure Boundary Bolted Flange Joint Assembly

2013

AS/NZS 2129 Flanges for pipes, valves and fittings 2000

AS/NZS 4331 (ISO 7005)

Metallic flanges – steel flanges 1995

AS/NZS 4087 Metallic flanges for waterworks purposes 2011

AS/NZS 4020 Testing of products in contact with drinking water 2005

AS/NZS 4623 Jointing compounds and materials for use in gas pipe joints

2008

ISO 7483 Dimensions of gaskets for use with flanges to ISO 7005 1991



Notes: 1. Available from Plastic Industry Pipe Association of Australia (PIPA) – www.pipa.com.au 2. Available from Plastic Pipe Institute (PPI) – www.ppi.org 3. Current issue at August 2014

2.0 Purpose

The purpose of this document is to review the various gasket solutions which are now available to suit Polyethylene (PE) pipe connections.

These are not mandatory requirements but are presented as best practice recommendations when designing gasket solutions for PE pipe connections.

3.0 Introduction

PE pipe and associated connections are now rated for use in a variety of demanding services, operating pressures and temperatures; these include water, waste water, potable water, gas and fuel.

It is important to make careful and appropriate gasket decisions to suit the specific requirements for each of these applications for the same reasons which apply when selecting gaskets for metal flange connections.

Whilst gasket-less connections are possible with these connections it is still common-practice to employ gaskets between (1) PE to PE stub flange connections, and (2) PE stub flange to metal flange connections. This document does not discuss gasket-less connections in any detail.

Since these stub flange connections generally employ metallic backing rings which are dimensioned to standard metallic flange dimensions such as ASME B16.5 one would be forgiven for assuming that the selection of the companion gasket standard such as ASME B16.21 would also be logical to apply. Unfortunately there are some key differences in these applications which make these standard gasket dimensions less than optimal in many PE connections.

It may also be shown that the inside diameter of gaskets has to be considered in relation to various gasket materials as well as pipe class in some cases.

4.0 Scope

In this document we consider gaskets to suit the two main connection arrangements in use:

1) PE stub flange to PE stub flange (Fig-1) and, 2) PE stub flange to metal flange (flat or raised face) – Fig-2

Pipe classifications AS4130 Class PE80 and PE100 across the available range of pipe SDR ratings are covered.

Various gasket styles such as ring, full face, and drop-in are also discussed here.

Various elastomeric compounds and compressed non-asbestos fibre (CNAF) material options are reviewed in detail.



5.0 PE Pipe classifications

HDPE piping is available in various pressure categories and wall thickness.

The most common standard in use in Australia is AS/NZS 4130:2009 Polyethylene (PE) pipes for pressure applications. There are two basic categories of pipe in this standard; PE80 and PE100. These are actually different compounds.

The pipe is classified by an SDR rating. This is the Standard Dimension Ratio of pipe DN to pipe wall thickness. The relationship between the dimensions of the pipes, the PE material classification and the working pressure rating are shown in table 1. For simplicity, the dimensions of the pipe have been referred to in terms of the Standard Dimension Ratio (SDR) where: SDR = (Outside Diameter) / (Wall Thickness).

Table 1-Comparison of SDR and Pressure ratings (PN)

SDR 41 33 26 21 17 13.6 11 9 7.4

PE80 PN 3.2 PN 4 - PN 6.3 PN 8 PN 10 PN 12.5 PN 16 PN 20

PE100 PN 4 - PN 6.3 PN 8 PN 10 PN 12.5 PN 16 PN 20 PN 25

6.0 PE Flange connections

There are two common connection methods in use. These are shown in Fig-1 and Fig-2 below and are discussed in more detail.

Figure 1- PE stub flange to PE stub flange

Fig-1 shows a typical PE stub flange to PE stub flange arrangement where the two stub flanges are held together using a pair of metallic backing rings.

Note the relationship of the gasket ID (right) which is scaled as per ASME B16.21.

The gasket with a reduced ID and thus increased stress area is recommended where low stress gasket materials such as elastomeric are used.



Figure 2- PE stub flange to Metal flange

Fig-2 shows a typical PE stub flange to Metal flange arrangement where the stub flange is secured with a metallic backing ring having the same standard dimensions as the metal flange.

Note the difference between the pipe bore of the metal and PE pipe. This needs to be considered when selecting gaskets for this style of connection.

The ASME B16.21 dimensioned gasket and similar would be appropriate when high compressive strength materials such as CNAF are used for gaskets.

Whilst Fig-1 and Fig-2 specifically reference ASME B16.21 for a gasket comparison the same relationship and scale will also apply to other flange standards which may or may not have companion gasket standards.

7.0 Metal backing rings

Metallic backing rings are discussed in detail in POP007. That document provides details of dimensions and requirements for backing rings according to flange standards listed in table 2 below.

Table 2 - Metallic backing ring flange standards covered in POP007

Standard Flange Classification Companion gasket standard

ASME B16.5 Class 150 ASME B16.21

AS/NZS 2129 Table D None

AS/NZS 2129 Table E None

ISO 7005-1 (AS/NZS 4331-1) Table 10 or PN10 ISO 7483

ISO 7005-1 (AS/NZS 4331-1) Table 11 or PN16 ISO 7483

AS/NZS 4087 Fig B7 and PN16 AS/NZS 1646 – material only

AS/NZS 4087 Fig-B8 and PN21 AS/NZS 1646 – material only

In terms of gasket selection the metallic backing ring selection is significant in that the gasket nominal size (DN or NPS) is actually based on this backing ring DN or NPS and NOT on the pipe nominal size (DN) directly.

Table 3 shows the relationship between pipe DN and metallic backing ring as well as metal flange DN or NPS for backing rings covered in POP007.



Table 3- Pipe DN to Backing ring/Flange/gasket DN per POP007

Pipe DN (Nom pipe OD)

Backing ring or flange DN (Gasket DN)

Backing ring/flange NPS (Gasket NPS)

AS

ME

B16

.5

AS

/NS

Z 2

129

ISO

700

5

AS

/NZ

S 4

087

mm mm inch

20 15 ½

25 20 ¾

32 25 1

40 32 1 ¼

50 40 1 ½

63 50 2

75 65 2 ½

90 80 3

110 100 4

125 100

125 125 5

140 125 5

160 150 6

180 150 6

200 200 8

225 200 8

225 225

250 250 10

280 250 10

315 300 12

355 350 14

400 400 16

450 450 18

450 500

500 500 20

560 550

560 600

630 600 24

710 700

800 800



Pipe DN (Nom pipe OD)

Backing ring or flange DN (Gasket DN)

Backing ring/flange NPS (Gasket NPS)

AS

ME

B16

.5

AS

/NS

Z 2

129

ISO

700

5

AS

/NZ

S 4

087

mm mm inch

900 900

1000 1000

8.0 Gasket types, styles

There are three basic styles of gasket to consider for these connections. The following is a discussion of the advantages and disadvantages of each style. The final selection preference is left up to end users.

Other gasket styles may also exist but are generally of proprietary design and are not discussed here.

Fig -3 Ring gasket style

End users should carefully consider if this gasket style will be suitable for their purposes and consider potential difficulty during fitting. Installers must juggle metal backing rings, studbolts as well as the gasket whilst trying to fit it centrally.

There is a high risk of misalignment with ring style gaskets without careful attention during installation.

Table 4 - Ring gasket summary

Advantages Disadvantages

Very economical Risk of misalignment is high

The same gasket may fit multiple connection classes since the OD and bolt holes do not need to be matched.

Fitting process can be more difficult

Fig -4 Full face gasket style

This is the most common gasket style employed and is recommended for all applications.



Table 5-Full face gasket summary


Easy to fit More expensive than ring style

Self-centrering Not interchangeable between different backing ring standards.

Fig -5 Drop-in gasket style

This is not in common use but is available as an alternative to full face gaskets.

Not generally recommended.

Table 6-Drop-in gasket summary


Easy to fit – only need to align two studbolts.

More expensive than ring style

Self-centrering Not interchangeable between different backing ring standards.

Bolt loads may not be evenly distributed.

9.0 Gasket material selection

There is of course a wide variety of gasket materials to choose from. The following guide provides some general information but gasket manufacturers should be consulted for best advice regarding materials for specific applications.

Table 7 provides a summary of commonly used gasket materials and their properties.

When selecting elastomeric gaskets ensure the elastomer is suitable for all intended media and specify good quality elastomers between 60-70 Shore A durometer hardness. Poor quality elastomers have poor compression set characteristics and contain a higher percentage of non-reinforcing fillers. Such elastomers will compromise the gasket performance and may not be able to support the stated pressure limits listed.

There are many other material options and proprietary gasket designs also available. Unfortunately it is not possible to review all materials here.



Table 7 - Gasket material selections

Details Units Elastomers (1) CNAF

Material type Nitrile Neoprene EPDM Sentinel INCA

Max operating pressure (4) bar (MPa)

8 (0.8) 8 (0.8) 8 (0.8) 100 (10) 100 (10)

Max operating temp Deg C 100 110 120 400 350

Minimum gasket operating stress

MPa 2 2 2 15 15

Maximum gasket initial stress MPa 10 10 10 50 50

Suitable for Gas (2)

Suitable for water, waste water

Recommended for Potable water (3)

(3) (3) (3)

1) Applies to reinforced and non‐reinforced good quality elastomeric sheet material but NOT specialised

gaskets with metal inserts or other unique designs. These designs may well be suitable for higher pressures

and different operating stresses.

2) Sentinel has AGA Gas approval to AS/NZS 4623 Class 3 up to 2,000 kPa

3) Potable water applications may require special grades of EPDM and may require approval to AS/NZS 4020

requirements in Australia. Details are available on request. Both Sentinel and INCA also have WRAS UK

approval for hot/cold water up to 85 deg C.

4) Operating pressures for CNAF can vary by thickness. Max values shown for info only and substantially

exceed PE pipe ratings anyway.

Gasket material selection may also affect gasket dimensions, in particular the gasket ID. See further details below regarding gasket ID vs material discussion.

10.0 Gasket dimensions

Unlike metal flange connections where it is quite common to use elastomeric gaskets on flat-face flanges, all PE stub flange connections need to be considered the same as raised face (RF) flange applications. This is because the PE stub flange effectively results in gasket contact areas quite similar to raised face applications. This is so even when a flat face metal flange is used on one side of the connection.

When determining optimum gasket dimensions the following requirements need to be considered:

1) Gasket stress area vs. studbolt stress area ratio 2) Maximum stress requirements for each different gasket material 3) Intrusion into pipe bore in case of PE stub flange to metal flange connections.

Table 8 below provides methods to use when determining gasket dimensions.



Table 8 - How to determine dimensional properties of gaskets

Feature Gasket style Criteria for dimensions Notes

Gasket OD Ring style Calculate Backing ring PCD minus 1 Bolt hole diameter

Full face, drop-in

Use OD of backing ring as per standard of metal backing ring selected

Same as backing ring OD

No of holes Full face, drop-in

Refer to flange standard applicable to backing ring

Same as backing ring

Hole dia. Full face, drop-in

Refer to flange standard applicable to backing ring

Same as backing ring

Gasket ID ALL styles Refer to guidelines shown at para 10.1 and table 9 below

Gasket thickness

ALL styles Refer to guidelines under heading “Gasket thickness”

10.1 Gasket inside diameter

This is a key requirement which needs to be considered along with the material selection.

In general, for elastomeric gasket materials, make the gasket ID closer to the pipe bore to maximise the stress area available. Conversely with high compressive strength materials such as CNAF it is important to ensure the stress area is not too high. Gasket IDs in line with ASME B16.21 are recommended for such materials.

We could attempt to establish a series of complex tables to list every gasket ID after considering each pipe/flange SDR, DN, stub flange OD and various gasket materials etc. Instead, we will present a set of relatively simple rules from which may be derived the suggested gasket ID.

Virtually all existing National and International gasket standards establish the gasket’s ID based on the nominal metal pipe OD. This is indeed the basis for ASME B16.21 etc.

Table 9 provides recommended practices when determining the gasket inside diameter.

Table 9-How to determine correct gasket ID

Gasket material Max operating pressure – bar

(MPa)

PE to PE connection

PE to metal flange connection

Elastomeric (1) 8 (0.8) Use Rule #1 Do not use

CNAF materials 100 (10) (2) Use Rule #2 Use Rule #2

1. As shown in table 7, applies to good quality, standard reinforced or non‐reinforced sheet material only.

2. These values exceed maximum rating of PE pipe and are shown for information only.

3.



10.1.1 Rule #1 definition

Define gasket ID based on mean pipe diameter for stated pipe DN and SDR rating per AS 4130.

Recommended for elastomeric materials. This approach maximises the available gasket stress area so that reasonable bolt loads may be achieved.

Not recommended for high compressive strength materials such as CNAF materials because the available flange bolt loads may be far too low to deliver the required minimum gasket operating stress with resultant joint failure or leakage, especially when factoring in the reduced maximum permissible flange stresses and recommended bolt loads for PE flanges. This is a typical cause of poor joint integrity and is often incorrectly attributed to the gasket.

It may also be possible and practical to define a common gasket ID to suit a range of pipe/flange SDR ratings per pipe DN thus reducing the overall variety of gasket sizes needed to be established. In such cases the calculated ID should consider the worst case pipe bore within the range required.

10.1.2 Rule #2 definition

Define gasket ID based on equivalent metal pipe OD relative to metal backing ring flange standard DN, Class. i.e.) Use ASME B16.21 dimensions or applicable gasket standard.

Recommended for CNAF materials. For these materials ASME B16.21 or applicable companion gasket standard dimensions should be used. Reducing the gasket ID to the mean pipe diameter is NOT best practice for these materials.

Not recommended for elastomeric materials. If gasket IDs equal to those listed for standard metal flanges are used the maximum initial stress of the elastomeric material may be reached at relatively low bolt stress values. See Fig-1 and Fig-2 above for relative scales.

10.2 Gasket thickness

THICKER gaskets DO NOT make better gaskets; this is the common creed of most gasket manufacturers and indeed the FSA and ESA which often goes unheeded. There are numerous valid technical reasons for this but the full discussion of these is outside the scope of this document. The following is a reference to an article covering this topic in detail which was published by FSA (Fluid Sealing Association) in 2005:

What gasket thickness should I use in my pump system?

Sealing Sense Article – Fluid Sealing Association www.fluidsealing.com/sealingsense/Oct05.pdf

The most common gasket thickness used for elastomeric gaskets is 3mm (1/8”). However, these normally only support relatively low operating pressures and this thickness is generally the most common sheet material available in a wide variety of compounds.

When selecting non-elastomeric gasket materials you should consider the thinnest practical gasket material to suit the flange conditions. In general, we suggest 1.5mm thick gaskets for non-elastomeric materials up to DN600. However, it must also be recognised and considered for existing installations the potential for a cumulative error in flange face separation over long pipe runs.

11.0 Bolt load/torque values

PPI document TN-38 discusses bolt load/torque requirements for PE stub flanges in detail. This document is recommended as a guide to determine the bolt load and torque for these applications.

Be aware that TN-38 primarily focuses on gasket-less solutions but also reviews the use of elastomeric gaskets and is still valid in determining the required bolt loads and stresses when gaskets are used.



Where the gasket material, pipe, flange DN or specific application is outside the scope of TN-38 both PE flange and gasket manufacturers should be consulted to determine a suitable bolt load solution.

ASME PCC-1 also provides detailed guidelines applicable to installation and gasket stress calculations if required.

Table 10 shows typical gasket and bolt load/stress values based on using elastomeric gaskets. The loads are based on targeting the maximum initial gasket stress of 10 MPa (table 7). Note the relatively low bolt stress values.

Table 11 shows the same data based on using CNAF materials but targeting a nominal gasket operating stress of 15 MPa – also per table 7.

Table 10- Sample gasket stress vs bolt stress data (Elastomeric materials)

Detail Units Example 1 Example 2

Pipe DN mm 160 160

Pipe Class (per AS4130) PE100 PE100

Pipe SDR 17 17

Operating pressure Bar (MPa)

8 (0.8) 8 (0.8)

Pipe connection type PE to PE PE to PE

Flange/backing ring DN mm 150 150

Backing ring flange standard ASME B16.5 ASME B16.5

Backing ring flange Class Class 150 Class 150

Gasket style Full face Full face

Gasket Rule applied (per table 9)

#1 #2

Gasket ID mm 140.7 168.3

Gasket OD (effective) (1) mm 212 212

Gasket contact stress area mm2 19,751 13,053

No of studbolts ea 8 8

Size of studbolts inch ¾ ¾

PE stub flange OD mm 212 212

Bolt stress area (total) mm2 1745 1745

Bolt stress MPa 112 76

Gasket stress (Initial) MPa 10 10

Gasket stress (Operational) MPa 9.3 8.9

Note:

1) Effective gasket OD is equal to PE stub flange OD for PE-PE connections.



Table 11- Sample gasket stress vs bolt stress data (CNAF materials)

Detail Units Example 3 Example 4

Pipe DN mm 160 160

Pipe Class (per AS4130) PE100 PE100

Pipe SDR 17 17

Operating pressure Bar (MPa)

16 (1.6) 16 (1.6)

Pipe connection type PE to PE PE to PE

Flange/backing ring DN mm 150 150

Backing ring flange standard ASME B16.5 ASME B16.5

Backing ring flange Class Class 150 Class 150

Gasket style Full face Full face

Gasket Rule applied (per table 9)

#1 #2

Gasket ID mm 140.7 168.3

Gasket OD (effective) (1) mm 212 212

Gasket contact stress area mm2 19,751 13,053

No of studbolts ea 8 8

Size of studbolts inch ¾ ¾

PE stub flange OD mm 212 212

Bolt stress area (total) mm2 1745 1745

Bolt stress MPa 184 135

Gasket stress (Initial) MPa 16.3 18

Gasket stress (Operational) MPa 15 15

Note:

1) Effective gasket OD is equal to PE stub flange OD for PE-PE connections.

12.0 How to order gaskets

As may be seen in table 3 above there are multiple examples where the same flange backing ring DN fits different pipe DN sizes. Therefore, in order to select the correct gasket for each application, the following minimum information should be supplied when ordering/specifying gaskets:

Essential data

1. Nominal PE pipe DN 2. Pipe classification from AS 4130 or pipe standard. I.e.) PE80 or PE100 only 3. SDR rating of pipe and PE stub flange (these are the same) 4. Nominal backing ring DN or NPS 5. Backing ring flange standard selected. Eg) ASME B16.5 Class 150, AS 2129 etc

6. Connection type…

a. PE stub flange to PE stub flange (assumed unless stated otherwise) b. PE stub flange to metal flange (raised face or flat face)

7. Required gasket style. I.e.) Full face ++ 8. Required gasket material ++ 9. Required gasket thickness ++



Application data (optional)

++ Instead of these values, if preferred you could supply the gasket manufacturer with the following details, in addition to the information stated above, and they will suggest a suitable gasket for you:

1. Operating media details eg) LNG, Water etc 2. Operating temp (max) 3. Operating pressure (max)

This information is based on our general experience, but because of factors which are outside our knowledge and control, no warranty is given or is to be implied with respect to such information. If any doubt exists, please seek advice from James Walker.

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technical report gaskets for polyethylene pe pipe connections

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