A Comprehensive Guide To Wall Wash Test (WWT) On Chemical Tankers

Jan 26, 2024

What is Wall Wash Test (WWT)? All non-chemical tanker folks must be wondering. You may have encountered this term at least once during your exam or sea time, but you’re still unsure about it. Don't worry; even if you’re a beginner or looking to join a chemical tanker for the first time, we’ve got you covered in this article.

The Wall Wash Test (WWT) is performed on chemical tankers after completing the tank cleaning operation of cargo tanks.

Wall Wash Test (WWT) is required to determine the vessel's cleanliness, which means whether the vessel is ready or not to load the next cargo and if further cleaning is required or not.

The Wall Wash Test (WWT) requires ship staff to enter the cargo tanks and collect samples from various locations.

An instrument called a spectrometer (UV Test apparatus) is generally provided on board by the vessel charterers or owners to perform the Wall Wash Test (WWT).

A spectrometer provides result data and UV scan graphs of Hydrocarbon (HC), Chloride (Cl), Permanganate Time Test (PTT), APHA colours, etc., which play a deciding role in determining whether the tanks are suitable for loading the next cargo or not.

Ship staff must familiarise themselves with the use of spectrometers on board to perform the Wall Wash Test (WWT) on board and to ensure compliance with the required cleanliness standards. The charterers may request the result data and UV scan graphs of the Wall Wash Test (WWT) at any time.

Once the vessel reaches the loading port, a cargo surveyor comes on board to take the wall-wash samples. Samples taken by the surveyor will be inspected at a shore-based laboratory. The cargo loading will commence only after the samples taken by the surveyor are passed.

Now for a better understanding of the Wall Wash Test (WWT), we will discuss the following:

Table of Contents

The Cargo Tank Cleanliness Standards for Chemical Tankers are defined in the INTERTANKO publication. These standards were developed to simplify the tank cleanliness verification process and reduce the need for in-tank inspections.

The primary purpose of these cleanliness standards is to provide predictability in terms of cost and time required for tank cleaning. Additionally, they aim to avoid tanks over-cleaning, improve port turnaround, clarify charter-party terms, and reduce the number of in-tank inspections in ports.

Cargo tank cleanliness standards are divided into four standards:

In the Visually Clean Standard, tanks are inspected from the deck level, and no Wall Wash Test (WWT) is required. Tanks must be clean, dry, and visually free of previous cargo residues and foreign matter. There should be no uncharacteristic odour.

In Water White Standard, tanks are inspected internally, and Wall Wall Wash Test (WWT) is carried out. Tanks must be odour-free, clean, dry, and visually free of previous cargo residues and foreign matter. In Water White Standard Wall Wash colour test is carried out with methanol, acetone, and other suitable solvents. The acceptable result of this colour test is 15 or less.

High-Purity Standard is commonly used for the carriage of Methanol cargo. This standard is often called the Methanol Standard. In High-Purity Standard, tanks are also inspected internally, and the Wall Wash Test(WWT) is carried out with methanol, acetone, and other suitable solvents. This standard also requires tanks to be clean, dry,odour-free, and visually free of previous cargo residues and foreign matter. The acceptable result values are mentioned below:

The Ultra-High Purity standard requires a more stringent level of cleanliness than the High-Purity Standard. It is used for the carriage of extremely high-spec cargoes.

In Ultra-High Purity Standard, tanks are also inspected internally, and the Wall Wash Test(WWT) is carried out with methanol, acetone, and other suitable solvents. This standard also requires tanks to be clean, dry,odour-free, and visually free of previous cargo residues and foreign matter. The acceptable result values are mentioned below:

Note: Non-volatile matter and Gas chromatography tests cannot be performed on board. For more details about Cargo Tank Cleanliness Standards for Chemical Tankers, please refer to the INTERTANKO publication.

Hydrocarbon (HC)/Water Miscibility Test

To make a test solution: Add 10 ml of the tank sample and 90 ml of Deionised water (D.I. Water) laboratory grade in a sample/nessler tube.

Note: Adding more methanol to DI water makes the hydrocarbon test progressively stricter. The dilution ratio depends on the company and load ports. Other commonly used ratios include (25:75, 33:67, and 50:50)

Chloride (Cl) Test

6. Now we have both the standard solution and the wall wash sample ready to run into the spectrometer.

Note: Chlorides must be less than 2 ppm.

Note: Permanganate time test(PTT) must be > 50 min.s

In addition to the aforementioned wall wash tests, other important tests are also carried out, such as

Visual Test: This test involves visually inspecting the sample under suitable lighting conditions to detect the presence of any suspended particles or visible impurities.

Odour Test: The odour test is performed to identify any persistent foreign odour that might contaminate the cargo. Filter papers are dipped into both the sample and the standard solution, and immediate smell detection is performed. It is crucial to avoid directly smelling from the tube, particularly if the previous cargo contained toxic substances.

Non-volatile Matter (NVM) Test: The NVM test aims to determine the presence of non-volatile impurities on the tank surface. A specific quantity of the wall wash liquid is evaporated, and the resulting residue (Non-volatile Matter) is weighed. The weight of the residue is then divided by the original sample weight to calculate the non-volatile matter content.

A test method is also available for determining the acid wash colour of various industrial aromatic hydrocarbons, including benzene, toluene, xylenes, refined solvent naphthas, and similar substances. This test provides a standardised procedure for assessing the acid wash colour of these hydrocarbons.

We are almost at the end, and we hope you have understood the concept of the wall wash test.

Now, you might be wondering what exactly is wash water analysis?

Well, in tankers, seafarers have to make multiple entries into enclosed spaces to comply with wall wash criteria before reaching the loading port. However, due to the past fatalities associated with enclosed spaces, the industry is shifting from wall wash to wash water analysis.

Wash water analysis involves analysing the wash water that is pumped out of the tank using a spectrometer to determine if the tank is clean enough for the next cargo.

With wash water analysis, it is possible to monitor the tank cleaning process in real time during the actual cleaning operation.

This approach helps to reduce the actual washing of tanks based on a fixed time or physical inspection, as the cleanliness can be accessed through the measurement of the wash water itself.

You might also like to read-

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used in the article, have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendations on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight.

Bhupinder Marriya is an experienced seafarer currently serving as a Third Mate on chemical tankers. Holding a Second Mate Foreign Going COC (Indian), Bhupinder possesses extensive knowledge of tank cleaning operations, navigation, and cargo work, along with expertise in life-saving appliances and fire-fighting equipment (LSA & FFE). Combining his practical experience at sea with a passion for maritime education, Bhupinder actively contributes as a freelance writer, sharing valuable insights and educating readers about the maritime industry.