This website section has been prepared to furnish broad overview type guidance to engineers who are charged with the responsibility of performing system-wide corrosion monitoring.  The information provided reflects a portion of Corrosion Resolutions knowledge and experience in this field.

The express purpose of the intended corrosion monitoring program is assumed to be determination of component/system materials adequacy.  Furthermore, we assume that the corrosion monitoring program will be conducted over a considerable period of time.   No information is furnished in this section for conducting non-steady-state, single point-in-time programs, such as those that rely totally upon coupon immersion tests.   Corrosion Resolutions experience clearly indicates that programs of this type provide significantly misleading information.  Therefore, this corrosion monitoring method should be avoided.

Given the foregoing background information, the following Corrosion Resolutions advice is provided:

It is the responsibility of corrosion engineers to produce a matrix of systems, subsystems and line segments versus projected potentially significant corrosion problems. Evaluation of the prospective impact(s) of these corrosion concerns will require the identification and classification of materials type, galvanic combinations present, water chemistry, temperature ranges, flow rate and conditions, layup practice, inhibitor and/or biocidal treatment practice, and operating conditions. As a single example, it is very important to identify whether the component to be monitored, e.g. a pipe segment, is in: a) continuous flow service;  b) intermittent flow service; c) wet standby service, or d) dry standby service.

Once the corrosion impact assessment has been completed, the identified corrosion concerns that will require monitoring should be listed and the preferred monitoring methods/alternatives should be identified. The basis of an effective and practical corrosion monitoring program will invariably be produced by this approach. Note: the table at the end of this section provides a brief summary of some of the various methods available for implementation in a corrosion monitoring program.

The design of a technically effective corrosion monitoring program is dependent upon utilization of an appropriate mix of monitoring methods, so that material performance data corroboration is achieved. In contrast, program cost control is established by limiting the amount of equipment and manpower that is necessary to establish and maintain an effective monitoring program. Invariably, there will be a conflict between the technical goals and economic constraints of any program. Nevertheless, an effective corrosion monitoring program can be devised that satisfies both the technical and economic concerns. This is accomplished by defining, through analysis, what must be evaluated, where in the system it must be evaluated, and by determining what monitoring equipment guidelines and criteria must apply. For example: 

1. Do not simulate, e.g. by use of test loops, unless it is absolutely necessary.   In-situ analysis is essential. This caveat does not apply to parametric studies of significant variables or confirmation of a corrective action concept prior to making a commitment to adopt it.
   
2. Determine the system baseline condition prior to starting the program. Note:  Do not select test methods that rely upon the use of new or reasonably clean spoolpieces to project long term performance of a substantially corroded and encrusted pipe.
   
3. Always use multiple test methods to assure that data corroboration is readily achievable in a non-destructive manner, but limit test method invasiveness.
   
4. Give due consideration to design related variables, e.g. turbulence at tees and elbows, static conditions in dead legs or in segments in static layup for protracted periods, etc.
   
5. Use well defined test methods and practices to the fullest practical extent.  ASTM G series test methods and practices are recommended.
   
6. To limit manpower, use automated instrumentation wherever possible. For the same reasons, use equipment having audible alarm set points for annunciation of significant changes in corrosion rate/corrosion mechanism. This instrumental feature limits the need for data reduction,  analysis time and permits technician level day-to-day operation.
   
7. Make real time analysis a primary program requirement because it:

• Rapidly confirms a steady-state condition, which is the only data that can reasonably be used for projecting remaining life
• Warns of environmental upset conditions that produce, e.g. dramatic changes in corrosion rate and/or corrosion mechanism.
  Real time analysis also occassionally provides an opportunity for program engineers to determine the corrosion cause, e.g. does excessive corrosion only occur when the system is static (MIC?) or does it only occur in response to certain known water chemistry changes?

8. Augment real time analysis with at least two other methods of monitoring so that data corroboration can be achieved.  As examples:

• One can use multiple station linear polarization equipment to establish corrosion rate and another form of potentiodynamic analysis for determination of the prevailing corrosion mechanism. However, the information obtained from these instruments should be verified by analysis of extractable coupons (which are evaluated by weight loss, metallography, etc.) and, e.g. quarterly ultrasonic testing of a previously baselined pipe segment or spoolpiece.

• In situations where either the coolant conductivity is too low to permit linear polarization (or a similar form of analysis) or in a situation where erosion-corrosion, e.g. at elbows, tees, etc., is the primary concern, use the electrical resistance method for analysis.

9. Assure that the program is designed to fully evaluate all significant factors such as:

Material Factors	Other Factors
Parent material chemistry and metallurgical condition	Design factors such as crevices, turbulence at elbows, galvanic incompatibility, etc.
Welds	Water chemistry
Surface Condition	Biocidal treatment
	Flowrate