Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Problems Caused by Obscurity in Coating Specifications

By Mark Davidson, Eng.
Published: August 15, 2019 | Last updated: January 31, 2022
Key Takeaways

Common disputes on coating application projects often originate in the coating specification. When the specification is unclear, it can lead to conflicts about what is required and what is acceptable.

Source: Mark Davidson

I’ve found that unless proper thought is given to the intent and writing of a coating specification or a procedure, it can lead to misinterpretations that can be costly. Clarity and definition is extremely important because without it, the people who are supposed to use the specification are unaware of exactly what the client wants.


This lack of clarity will lead to misunderstandings, possibly incorrect work, delays, disputes and inevitable additional costs. So I am a great believer in clarity and definition in a specification—really, in any project document, but particularly in the specification, as it is the controlling deed in a coatings project.

There are common phrases that occur in certain sections of coating specifications, written by people who are probably just not thinking about what they are writing and not considering the ramifications of what they are writing. Some prime examples are often found in the requirements for surface preparation.


Weld Preparation Quality

In new construction, preparation of welds is done before any surface preparation starts. Any steel object, unless it is a totally bolted structure, will have many meters of welds in it. A ship will have hundreds of kilometers of welds. Therefore, clearly defined statements in a specification about weld quality and finish are extremely important because welds can become an area for early coating breakdown due to localized, reduced coating thickness. (Learn how coating thickness is measured in the article 7 Methods of Coating Thickness Measurement.)

Here is a sample phrase found in the surface preparation section of a coating specification:

“Weld spatter, slivers, inclusions, mill scale, rust, slag, undercuts, laminations, and similar surface defects or irregularities shall be removed.”


This statement implies that all of the above are defects and shall be removed. In an attempt to clarify, the writer states that the AWS D1.1 standard weld profiles shall be acceptable. However, that standard allows tightly adherent spatter.

So should the welding contractor remove all welding defects, or are some defects acceptable? The two statements conflict.


The specification engineer should have simply referenced the AWS D 1.1 standard, or similar ISO 8501-3 for weld profiles instead of describing what was considered to be weld defects and requiring their removal. A lack of clarity and definition regarding weld preparation can be avoided by simply referencing the applicable standard(s) and stating the required standard of finish. (The role of corrosion is discussed in An Overview of Welded Joint Corrosion: Causes and Prevention Practices.)

Abrasives and Surface Cleanliness

Another area commonly affected by a lack of clarity is the quality of abrasives. A typical specification states:

“Abrasives shall be clean, dry, sharp, angular, and free of clay, salt and oil,” and, “Abrasives shall not leave excessive residue on the surface.”

However, a certain quantity of contamination is generally acceptable and the test methods for determining their presence and concentration are included in standards such as the ISO 8502 series, which were referenced in this particular specification.

So, the requirement that all abrasives shall be clean, dry, sharp and angular; free of clay, salt and oil; and shall not leave excessive residue on the surface is contrary. This causes confusion and leads to loss of time, the need clarify and likely additional costs.

Rather than trying to control the abrasive quality, the specification engineer should have concentrated on controlling the effect of the abrasives, which is surface cleanliness.

All he/she needed to state was:

“Surface cleanliness at the time of painting shall meet the specified requirements. It shall be SA 2½, in accordance with ISO 8501-1. The permissible maximum dust level is grade 2 measured in accordance with ISO 8502-3. The residual salt level shall not exceed 20mg/m2 as per ISO 8502-9. Abrasives used in this work shall produce the foregoing surface cleanliness.”

Cleanliness standards can be varied for specific materials and service requirements. This way, all parties understand what is required. The specifying engineer can do away with these unclear statements, which just cause confusion.

Faulty Rule of Thumb: Time Frame to First Coat

The following issue can cause problems for both painting contractors and coating inspectors. I regularly see this industry rule-of-thumb statement in coating specifications and procedures:

“The maximum period between the completion of surface preparation and the application of the first coat, or primer, shall not exceed 4 hours.”

Sometimes this time frame is acceptable and appropriate, but other times it is not.

If the environment and ambient conditions (humidity, temperature) are such that the surface quality does not deteriorate (for example, flash rusting), the surface cleanliness quality could persist for 24 or 48 hours. I’ve seen large offshore platform blocks in coating shops where the environment is humidity and temperature-controlled, and those blocks have retained the required surface cleanliness for up to seven days before the first coating is applied. You can do that in controlled environments.

Similarly, if you have structures in an outdoor area where the relative humidity is low enough, where the atmospheric conditions are such that you can maintain the surface preparation quality, then that is quite acceptable.

So the four-hour limit is a potentially conflicting requirement that can be very limiting for the contractor, and it will cause problems. I’ve known it to cause issues for inspectors, who are expected to enforce a specification with that requirement in it. It’s unrealistic and unhelpful for all parties.

The only way to clearly define this is to say:

“The surface preparation quality shall meet the [cited] standard at the time of coating application,” because that is exactly what is required.

"Good'' and ''Clean''

Subjective terminology commonly used in the industry, terms like “good” and “clean”, leave it open for different interpretations to be made. Therefore, it is important to reference specific standards that give the contractor and the inspector a recognized, measured way to determine the acceptable level of cleanliness. (Surface preparation is discussed in Substrate Surface Preparation for Corrosion Prevention.)

So it’s extremely important to reference the right standards to set parameters. All of the pertinent ISO, NACE, SSPC and other industry standards provide the means to measure many of the characteristics in coating operations, which then allow the specifier to state the acceptable levels for each in a coating specification.

Doing it this way provides the necessary clarity and definition. Those requirements can then be included in the Contractor’s Procedure and the Inspection and Test Plan documents. So when quality control activities are carried out, all parties have a clearly stated parameter that they must inspect for, in order to determine whether the specified quality has been met.

A Case of Climbing Costs

Here is a case where conflicts between the welding specification and the coating specification caused expensive delays by requiring that welding surfaces be reworked. When constructing a new offshore platform, the topsides are made in blocks, which are welded and then sent to a shop for painting. On this particular project, the owner had a conflicting requirement in his specification about the need for a certain weld finish or quality.

It is common in fabrication yards for the subcontractors who do the welding, and grind and prepare the welds for painting, to have a certain standard they work to. They know that they can achieve a particular production rate when working to that standard.

In this case, the yard weld quality standard was less than the client’s coating engineer believed was necessary to achieve the desired coating durability.

The coating engineer looked at a number of blocks before they were due to go to the painting shop and he said, “Now this weld quality is less than we require.” But the contractor said to him, “Well, your welding specification says this and we have complied with it, but your coating specification requires something better.”

The blocks were held back and delayed from going to the coating shop while meetings were held and copious correspondence changed hands. The welding specification and the paint specification were both client documents and finally, the client required that the coating specification should be the controlling document.

The client then had to pay extra money for additional weld grinding and preparation to be done to meet the coating specification requirements.

Not only can you have lack of clarity in one particular specification, you can also have lack of clarity, or conflicts, between two different client specifications on one project. It is important that the different disciplines, such as the structural engineer and the welding engineer, talk to the coating engineer to ensure that all of the requirements for proper coating are clearly written into the welding specification.

Inevitably in this case, there was a that cost the owner had to pay for this additional grinding to be done.


Disputes, delays and additional costs can arise on coating projects due to a lack of clarity and definition in documents. However, if there is focus on these vital ingredients by the writer and reviewers of coating specifications and procedures, most of these issues can be avoided.

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Written by Mark Davidson, Eng.

Mark Davidson, Eng.
Mark has worked more than 35 years in the corrosion protection industry mostly in the Oil and Gas sector. He started out on an operating oilfield and progressed to the engineering services industry specialising in protective coatings for steel structures as well as pipeline and subsea equipment coatings. His work took him to many fabrication yards and pipeline construction spreads where he learned the value in getting your hands dirty as well as the need for clarity and definition in specifications and project documents.

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