Investigating a pipeline piercing ??

Very often, when a leak is detected, repairs are performed immediately and pierced pipe sections are cut, cleaned, stored in bad conditions or lost (if not scrapped). It results in a difficult analysis of the corrosion causes. The roles of employees are not always very clear: who does the investigation? What has to be done first? Which samples or data need to be collected? Etc.

The article presents basic rules to collect efficiently the corrosion evidences which help in the analysis of the phenomenon. It requires a basic organization (who does what), a simple set of steps to follow and a list of data and samples necessary to collect.

This article is inspired by the first chapters of Field Guide for Investigating Internal Corrosion of Pipelines, Richard Eckert, NACE Press and it is advised to read it carefully to get a complete overview of corrosion investigations. Richard Eckert has published many books and papers providing practical and scientific approaches to corrosion phenomena. Read them!

We will not explain corrosion mechanisms which are various and complex (we will propose some articles about them shortly).

1. THE CORROSION INVESTIGATION PLAN

The “Corrosion investigation plan” describes how the Operator is organized to manage a pipe leak investigation. This docuemnt covers the responsibilities, the management of the records, the procedures and the material.

?Responsibilities:

?The personnel or department which conducts field investigations, coordinates and manages all investigations and testing, and which reviews the results should be clearly identified.

?Records:

?All data and results should be archived in a way that allows:

• Easy access to the data
• Easy comparison: use standard templates, same units for each investigation.
• Track evolution of corrosion problems in time. If two leaks appear on the same network, having a proper set of data will help you understanding if they have the same cause (or not).

Samples (pieces of pipes, of liquids or gas) should be kept protected and preserved from rust as long as issues have not been completely solved. Once your failed piece of pipe is exposed to the oxygen and moisture from the air, another type of corrosion will occur and may hide the origins of your problem.

?Procedures:

The Operator shall have proper procedures or rules concerning corrosion investigations that shall comply or be coordinated with:

• HSE internal and regulatory rules
• Emergency response program
• Management reporting system

?Primary toolbox:

?The personnel or department in charge of the investigations should have at least the following tools:

·??????pH meter
·??????Camera
·??????Wall thickness meter (ultrasonic thickness gauge)
·??????Steel tape
·??????Small finely divided steel ruler
·??????Personal protective equipment (PPE) and gas detectors.        

2. INVESTIGATION STEPS

?As said by Richard Eckert,

"[the following rules] seem deceptively simple; however they require thought and attentiveness from the investigator who is present to observe and collect as much information as possible."

?When a leak is detected:

1. ?Application of the leak mitigation plan (including HSE measures, choice of a repair solution, production shut-down, …).
2. ?Personnel in charge of the investigation should be sent on site as soon as possible, before the pipe is cut or repaired.
3. ?Personnel which will collect evidences (cut pipe section, pictures, samples, etc) can start activities when safety conditions are met.
4. ?Ensure that all safety and environmental rules are respected during the investigation: appropriate PPE, permanent control of H2S or explosive gas, etc.
5. ?Take pictures of the leak location (pierced pipe in situation) and of the surrounding area.
6. ?Identify whether the leak is due to internal or external corrosion (shape of the hole)
7. ?Protect and collect all evidences. Elements which are wet at the time of sampling should be kept moist and protected from air exposure. See next paragraph for ideal samples to be collected.
8. ?Take pictures (macro and large) of all collected evidences and record the exact place they are coming from. Identify each picture and indicate the flow direction.
9. ?Cold-cut the samples and ensure that the failure point will not be altered by cutting operations or cleaning operations.
10. ?Transport and store the pieces of pipes and other evidences in a way that avoids corrosion progress (ie: don’t store it outside, do not clean with high pressure water jet, etc). Keep them inside with low moisture.
11. ?Collect as much information as possible (see the check lists below).
12. ?Once samples and data have been correctly collected, it is time for the analysis: call an internal or external expert (known or recommended), send samples to laboratory if needed.
13. ?Report all your findings to your management and request appropriate support to get satisfactory results.

3. SAMPLES

Ideally, elements to be collected can be

Pipe samples:

• From corrosion leak or failure site: cut the pipe section which has been pierced (this is not mandatory for external corrosion). Note the geographical location of this section, how the leak has been discovered (ILI, visual inspection, leak observation…) and every detail that can be useful for the investigation (see next section).
• From undisturbed pipe: Obtain a section of the pipe where there is no leak or rupture to understand what happened before leak occurred.
• Sample cleaning: Note every detail before cleaning the pipe for further investigation. Do not forget that cleaning the pipe (water, sandblasting, etc) alter the evidence (rust can be removed, visual aspect can be changed).

Liquids:

• From source: for gas pipelines, identify potential liquid sources (condensates and water) upstream of the corrosion investigation site and collect samples. For liquid pipelines a sample of the flowing liquids should be collected and analyzed.
• From corrosion site: when the pipe is first exposed and cut open, collect liquid sample for analysis.

Gas:

• From source: for gas pipeline, gas sample shall be collected from all potential upstream sources.
• From corrosion site: pipe will be purged in case of leak or failure. If corrosion site is close to a well, it would be useful to collect a gas sample for analysis.

Others: sludge, deposits, Scale, nodules, biofilms, bacteria or biological matter, coating for pipelines that are internally or externally coated.

4. CHECK LISTS

Go to Sanorah's blog to get investigation check lists' samples!

ABOUT SANORAH

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#corrosionprotection #corrosionmonitoring #corrosioncontrol #pipeline #pipelineintegrity #integrity #oilandgas #integritymanagement #leakdetection #coatings #coating