Piping Wastage Allowances

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Piping Inspection

Transcript of Piping Wastage Allowances

CONTENTS

Acceptance criteria and methods for evaluation of corrosion thinning in Carbon Steel Piping.

CONTENTS

31.General

2.Types and causes of corrosion33.Bureau piping corrosion experience44.Industry Codes and standards and other Classification societies6Industry Codes and Standards64.1A short description of these standards is described as follows:64.2ABS Rules for Building and Classing Steel Vessels 200574.3ABS Rules Survey after Construction 200574.4Some additional inspection/assessment methods in the industry are:84.5Feedback from other Class Society85.Overview of acceptance criteria Procedure86.Procedure for pipe corrosion assessment97.Examples of applying pipe corrosion assessments107.1Service: Salt Water Pipe Example 1107.2Service: Salt Water Pipe Example 2107.3Service: Fuel Oil Line On Deck Example 3117.4Service: Fuel Oil Line Passing Thru Fuel Tank Example 4118.Supplementary pipe data29

8. Procedure9

9. Tables

9

9.1 Table Minm. Wall Thickness for Steel Pipes..10

9.2 Table Commercial Pipe Sizes and Wall Thickness.11

9.3 Table Corrosion Allowance for Steel Pipes. 12

10. ASME B 31G Procedure13

11. Flowchart 14

12. Table Values of L for pipe sizes NPS 2 and < NPS 6..15

12. Table Values of L for pipe sizes NPS 50.8 mm and < NPS152.4 mm

16

12. Table Values of L for pipe sizes NPS 6 and < NPS 1017

12. Table Values of L for pipe sizes NPS 152.4 mm and < NPS 254mm

18

12. Table Values of L for pipe sizes NPS 10 and < NPS 16 19

12. Table Values of L for pipe sizes NPS 254 mm and < NPS 406.4 mm20

12. Table Values of L for pipe sizes NPS 16 and < NPS 2022

12. Table Values of L for pipe sizes NPS406.4 mm and < NPS 508mm24

12. Table Values of L for pipe sizes NPS 20 and < NPS 2426

12. Table Values of L for pipe sizes NPS 508mm and < NPS 609.6 mm28

13. Examples30

1. General

This document provides acceptance criteria and methods for evaluation of corrosion thinning in carbon steel piping. The details are to assist the Surveyors in determining the acceptable corrosion limits for piping systems in service.

The ABS Steel Vessel Rules provide requirements for the design approval of new piping systems, whereas details related to acceptance criteria for corrosion of piping in service is not available.

This document is divided into four sections:

1) Types and causes of corrosion

2) Rules and Industry standards available

3) Inspection and Testing methods

4) Recommended approach for Marine piping systems and Marine piping systems of MODU and Floating Production Installations.

The process piping systems for MODU and Floating Production Installations have not been covered in this document because of a separate approach which will be addressed in the future.

2. Types and causes of corrosion

There are many causes of thinning of pipes due to corrosion. Some of the principal causes are:

1) Pitting

2) Erosion and Erosion/Corrosion

3) Electrochemical process

4) Microbiologically Influenced Corrosion (MIC)

Following is a short description of the causes of corrosion in pipes:

1) Pitting:

Pitting is defined as localized regions of metal loss which can be characterized by a pit diameter on the order of the plate thickness or less, and a pit depth that is less than the plate thickness.

The types of pitting experienced are:

Localized or confined within a Local Thin Area (LTA ).

Widespread or a LTA located in a region of widely scattered pitting.

2) Erosion and Erosion /Corrosion:

This is the removal of surface material due to impact of solid or liquid particles and normally occurs in areas of turbulent flow or change in direction of flow. A combination of erosion and corrosion results in significantly greater metal loss than can be expected from corrosion or erosion alone.

3) Electrochemical Process:

This is caused by an electrochemical reaction between two dissimilar metals in an electrically conductive environment.

4) Microbiologically Influenced Corrosion (MIC):

This is caused by the presence of various microbiological agents under specific environmental conditions. This is very common in HVAC systems and produces large pits.

3. Bureau piping corrosion experience

The following data was obtained from O2K reports related to pipe failures. The systems with the most reported failures (as of June 2005) attributed to corrosion were as follows:

SystemNumber of reports

Ballast System22

Sea Water System14

Fire Main System14

Steam System13

Cargo Fuel Oil Pipe3

Fuel Oil1

Air Line1

Bilge System1

Offshore Piping Systems1

From these reports are listed some representative observations concerning the particular system.

Ballast System:

1) Ballast piping in No. 5 center double bottom ballast tank, pitted.

2) 8 inch ballast piping on main deck starboard of Cargo Hatch # 1 was noted to be leaking. The pipe had been fitted with a temporary soft patch

Sea Water System:

1) Seawater crossover main manifold and several smaller lines in engine room bilges found corroded and repaired with doubler.

2) The following seawater piping pieces were found wasted over 25% of original wall thickness, and replaced at the owners discretion:

3) The 20 inch waster piece at the combined overboard located outboard.

4) The 10 inch diameter manifold penetration at the Sprinkler Pump overboard discharge.

5) The low sea chest 30 inch penetration piece and the flanged waster piece adjacent to it.

6) The 24 inch flanged waster piece.

7) The 4 inch waster piece of the Distiller Plant Condenser overboard line.

Fire Main System:

1) The 4 inch diameter fire main piping located starboard side main deck forward of house at Frame No.26 had signs of failure due to wastage and was repaired by cropping approximate two and one-half foot section of the wasted piping, installing new schedule 80 seamless steel pipe and 150# slip-on flanges and welding using approved materials, weld procedure and welders.

2) On lower level of engine room port side inboard of fire and general service pump, corroded pin holes were found in 6" fire main piping.

Steam System:

1) Heating Coils in various Fuel Oil Tanks found leaking.

2) Pinhole leak observed on Boiler blow down Line (Reported in a number of cases).

Cargo Fuel Oil Pipe :

The original fuel oil piping in way of No. 5 centerline double bottom was soft patched due to excessive wastage. The heated fuel oil inside the piping in way of ballast tanks has caused the proliferation of fuel oil piping wastage.

Fuel Oil Pipe:

1) Heating Coils in various Fuel Oil Tanks found leaking.

2) Pinhole leak observed on Boiler blow down Line (Reported in a number of cases).

Service Air System:

Service air pipe on Port side upper deck heavily wasted.

Bilge System:

The bilge system six-inch diameter steel pipe located in the aft engine room bilge, Frame 121-128, was reportedly found with an approximate 20 foot section wasted, thinned and leaking. Upon completion of fabrication the new sections of piping was examined, shop hydro tested at 50 psig and found satisfactory

Offshore Pipe Corrosion failure:

The mud pipeline system mainly on the elbows and T-unions in various locations were found corroded.

4. Industry Codes and standards and other Classification societies

Industry Codes and Standards

There are various industry codes and standards relating to piping systems. Some of the common standards are listed as follows:

ASME B 31G - Manual for Determining Remaining Strength of Corroded Pipelines.

DNV RP-F101 - Recommended practice for Corroded Pipelines.

RSTRENG (Remaining Strength) Technology for use in evaluating the remaining strength of a pipeline when exposed to corrosion.

ASME B31G and RSTRENG are approved technologies by DOT.

4.1 A short description of these standards is described as follows:ASME B 31G

1) Used extensively for evaluation of Structural Integrity of Pipelines with Corrosion caused metal loss

2) Table for Corrosion Limits compares Longitudinal extent and maximum Depth of corroded area.

3) It is Conservative compared to other methods like RSTRENG and DNV RP-F101.

RSTRENG (Remaining Strength)

1) Designed to evaluate remaining strength of externally corroded pipe

2) Provides more accurate assessment of corroded area compared to other methods

3) Less conservative than ASME B 31G

4) PC based Program, therefore difficult to use in the field by Surveyors.

DNV RP F101

1) Uses empirical formula to calculate piping failures.

2) Unsuitable for Surveyors at locations.

4.2 ABS Rules for Building and Classing Steel Vessels 2005

Some of the survey requirements for new pipes in ABS Rules are as follows:

1) For new pipes, the wall thickness is calculated, which includes the corrosion allowance. This was added in ABS Rules in 2000 as per IACS UR.

2) Chemical cargo and Process piping are excluded from the scope.

3) Class 1 & 2 Pipes are Hydro Tested at 1.5 x P, where P is the design pressure.

4.3 ABS Rules Survey after Construction 2005

The Rules for Survey after Con