Guideline for Selection of Instrument Tubing And

8/10/2019 Guideline for Selection of Instrument Tubing And

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Statoil advisory document

Guideline for selection of instrument tubing and clamps for offshore

and onshore plantsTechnical and professional description, TD0101, Final Ver. 1, Valid from 2005-04-18Publisher/follow-up: TEK PE D&V, Hans von der Lippe

Classification: Open

Validity area:

UPN/Norway/All value chain/On- and offshore

1 Introduction.......................................................................................................................................2

1.1 Objective.............................................................................................................................................2

1.2 Warrant ...............................................................................................................................................2

2 Requirements.....................................................................................................................................2

2.1 Location and service ...........................................................................................................................2

2.2 Material selection................................................................................................................................2

2.3 Painting and insulation........................................................................................................................3

2.4 Inspection during operation ................................................................................................................3

3 Definitions..........................................................................................................................................4

4 References..........................................................................................................................................4

App A Table 1 Material selection for instrument tubing and other components ...................................5


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Guideline for selection of instrument tubing and clamps for offshore and onshore plants

Technical and professional description TD0101, Final Ver. 1, Valid from 2005-04-18

Validity area: UPN/Norway/All value chain/On- and offshore

Classification: Open Page 2 of 6

1 Introduction

1.1

Objective

The objective with this guideline is to give premises for optimised material selections for instrument

tubing and to avoid corrosion (i.e. crevice corrosion, etc.) between the instrument tubing and clamps

for offshore and onshore installations. It is recommended to use this guideline for new projects and

when performing modification projects onshore and offshore.

1.1.1 Background

This document is produced on the bases of experienced crevice corrosion problems on instrument

tubing at several installations onshore and offshore (i.e. Sleipner, Troll A, Kollsnes gas plant,

Gullfaks), see reference (1).

1.2 Warrant

This document is linked to the following documents:

Operation, maintenance and modifications (AR12) (Statoil group/All locations/On-and offshore)

Norsok M-001 Material Selection (ST061)

Norsok M-501. Surface preparation and protective coating (ST018)

Norsok M-630 Material data sheets for piping (ST071)

Norsok M-650 Qualification of manufacturers of special materials (ST072)

Norsok I-001 Field Instrumentation (ST007)Norsok R-004 Piping and equipment insulation (ST078)

L-SP-200 Piping and valve specification (TR2000)

2 Requirements

2.1 Location and service

Material selection for instrument tubing and other components including instrument clamps for

onshore and offshore installations are listed in table 1 in Appendix. The table consists of two main

groups, i.e. material selection in saliferious marine atmosphere and in non-saliferious atmosphereincluding indoor and dry conditions.

2.2 Material selection

The material selection shown in table 1 is based on Norsok standard M-001 and field experience at

different Statoil installations and should when implemented minimise the risk for corrosion problems

as crevice corrosion, CSCC, etc. The general recommendation is to use type 316 stainless steel tubing

for indoor service and type 6Mo stainless steel or type 25 Cr duplex in external marine and saliferious

environments. All instrument tubing for seawater services shall be in titanium materials.


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The material selection using type 6Mo and type 25 Cr duplex stainless steels should be safe for normal

temperature conditions for instrument tubing, but there may be a small risk for initiation of crevices

under long periods with wet and chloride containing conditions at high temperatures and between very

tight and critical crevices. A more extreme but partly relevant reference is the Avesta Handbook (2)

with crevice corrosion test results for type 316 and 6Mo materials in natural seawater at ambient

temperature as well as at 70oC. After 6 months of submerged testing in ambient seawater there was nocrevice corrosion on type 6Mo samples, but severe crevice corrosion on all type 316 samples. At 70 oC,

one of fifteen samples showed initiation of crevices on type 6Mo samples and all type 316 samples had

crevice corrosion . Based on these test results it is concluded that type 6Mo material should be

acceptable for use in marine atmospheric conditions and will be a much more robust material selection

than the standard type 316 stainless steel.

Type 25 Cr duplex material is considered to have same crevice corrosion resistance in marine

environments as type 6Mo material. See also Norsok standard M-001.

Based on experience in Company different material grades can be used for respectively instrument

tubing and for instance manifolds, valves, etc. As crevice corrosion under clamps has been the main

corrosion problem the up-grading of tubing material should solve this corrosion problem without a

need to up-grade material selection for manifolds, valves, etc. However, temperature restrictions for

selected materials shall apply according to table 1.

For seawater service titanium shall be used. Components shall be in material grade Hastelloy C-276.

Service restrictions for titanium will follow guidelines in Norsok standard M-001. Temperature

restriction for Hastelloy C-276 is recommended as maximum 30 oC in chlorinated seawater.

Temperature and environment restrictions for materials not listed in table 1, see Norsok standard

M-001.

Material selection of instrument tubing in other environments not listed in table 1 and services shall be

evaluated especially.

Manufacturers of type 6Mo stainless steel and type 25 Cr duplex tubing shall be qualified in

accordance with Norsok standard M-650.

Non-metallic clamps shall be used if there is a risk for vibrations of instrument tubing.

2.3 Painting and insulation

Painting shall be applied on instrument tubing to be insulated (i.e. heat traced) and in accordance with

Norsok standard M-501. It is recommended to reinforce the painted surfaces under clamps with a

heavy duty mastic coated tape system. Pre-insulated tubing systems may be selected pending approval

by Company.

Non-metallic clamps are preferred when instrument tubing is painted.

2.4 Inspection during operation

Inspection should be planed for and performed on instrument tubing under clamps within three yearsafter completed commissioning at installations. Based on experience the most critical areas should be


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selected for visual inspection. If no corrosion is observed, the actual inspection area may be deleted

from the inspection program.

3 Definitions

PRE Pitting Resistance Equivalent.

PRE = % Chromium + 3.3 x % Molybdenum + 16 x % Nitrogen

Type 6Mo Austenitic stainless steel alloys with 6% Mo and PRE>40.

Type 316 Austenitic stainless steel alloys with 17% Cr, 12% Ni, 2.5% Mo

22Cr Duplex Ferritic/austenitic stainless steel alloys with 22% Cr

25Cr Duplex Ferritic/austenitic stainless steel alloys with 25% Cr and PRE >40

Ti grade 2 and grade 5 Titanium alloys

Hastelloy C-276 Nickel base alloy with PRE>40

Operating temperature The temperature in the equipment when the plant operates at steady state

condition, subject to normal variation in operating parameters.

Crevice corrosion Form of localised corrosion caused within crevices in a corrosive mediumPitting corrosion Form of localised corrosion causing sharply defined holes on surfaces in a

corrosive medium.

CSCC Chloride Stress Corrosion Cracking

SSC Sulphide Stress Cracking

4 References

C025-S-0000-J-RE-001, Erfaringsrapport: Anbefalinger av instrumenttubing og klammer,

gyldighetsomrde land og hav, datert 15/7-2002.

Corrosion Handbook, Avesta Sheffield AB, 1994


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Guideline for selection of instrument tubing and clamps for offshore and onshore pla

Technical and professional description TD0101, Final Ver. 1, Valid


Classification: Open

App A Table 1 Material selection for instrument tubing and other components

Atmosphere/

fieldenvironment

Service

(Note i)

Material for

instrumenttubing

Material for other

components i.e.fittings/small

valves.

Maximum

temperature tominimise risk of

external CSCC.

Maximum

temperatureto minimise

risk of

internal

crevice

corrosion

(Note iv)Hydrocarbon

& hydraulic

Type 316 Type 316 Max 60oC(Note iii) N/A

Instrumentair

Type 316 Type 316 Max 60oC(Note iii) N/A

Sea water Titanium grade 2 Titanium grade 2 and 5

Hastalloy C-276

N/A

N/A85

oC

30oC

Indoor and

dry

atmosphere

or

External non-saliferious

atmosphereFresh water Type 316 Type 316 Max 60

oC(Note iii) N/A

Hydrocarbon& hydraulic

Type 6 Mo25 Cr duplex

Type 316Type 6Mo

Hastalloy C-276

Max 60oCfor type 316

Max 110oCfor type 25Cr

Max 120oCfor type 6Mo

N/AN/A

N/A

Instrumentair

Type 6 Mo25 Cr duplex

Type 316Type 6MoHastalloy C-276

Max 60oCfor type 316



N/AN/AN/A

Sea water Titanium grade 2 Titanium grade 2 and 5

Hastalloy C-276

N/A

N/A85

oC

30oC

External and

saliferious

marine

atmosphere

Fresh water Type 6 Mo

25 Cr duplex

Type 316

Type 6MoHastalloy C-276

Max 60 oCfor type 316



N/A

N/AN/A


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Notes:

1. See Norsok standard M-001 for sour (H2S /SSC) service restrictions.

2. Optional for use of metal or polymer type clamps.

3.

Maximum operating temperature of 70oC indoor or in sheltered areas for type 316 stainless steel.

Non-insulated systems.

4.

A maximum temperature for risk of initiation of crevice corrosion will apply. Maximum 30oC inchlorinated seawater is recommended.

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Guideline for Selection of Instrument Tubing And