Using compressed air as a propelling agent to transport pigs through pipelines is relatively unheard of in Europe. However, Brenntag Oil & Gas Europe has just used such a technique to clean a 140km section of the 60.96cm diameter crude transport line at Total’s refinery in Vlissingen, the Netherlands.

The company also used its own, patented N-SPEC cleaning chemicals. Together with the compressed air, the chemicals removed all hydrocarbons from the pipeline and as such bring the lower explosion level (LEL) down to zeropercent.

"The 140km crude transport line, the lifeline for Total’s refinery, had to be modified at two places, and some of the block valves had to be overhauled in order to safeguard the operation of this line for coming years," said Peter Verkiel, product manager at Brenntag Oil & Gas Europe and manager of the project. "To perform these activities, the transport line had to be emptied and cleaned, and most importantly, the environment in the line had to be safe, meaning no danger of explosion during welding and cutting activities. The maximum allowed LEL in this respect was 10percent or less," he added.

To add to the challenge, the project also had to meet a series of additional Total requirements: it had to be fully executed within five weeks; compressed air had to be used as a propelling agent to transport the pigs through the pipeline; minimum waste disposal; and a host of other safety precautions specified by the company.

Visser & Smit Hanab, a pipeline construction company who was the main contractor for the complete project, called Brenntag in for the cleaning part and to achieve this low LEL within the pipeline by means of its N-SPEC advanced chemical cleaning services.

"Over the years, this product has proven to be a more effective cleaning agent and less hazardous than traditional cleaning agents," noted Verkiel.

A multi-phase project

Prior to the actual execution of the project, Brenntag cooperated with the client to develop a project execution plan, documenting all elements of the project, and a risk inventory and evaluation (RIE) analysis of all possible risks and measures to reduce them to an acceptable level for both Brenntag and the client.

The project had been split into three different phases: phase one, online
pre-cleaning of the pipeline with several pigging runs; phase two, removal of the crude and offline cleaning of the pipeline with N-SPEC50 and N-SPEC120, in one single pigging run, followed by cutting/welding services; phase three, refilling the line with crude.

After both parties agreed on the complete set-up, Brenntag commenced the first phase of the execution (Fig.1).

Pre-cleaning

The first phase involved the pre-cleaning part of the operation. Laboratory tests indicated that N-SPEC50, a special wax and paraffin dispersant, and N-SPEC120, a multi-purpose cleaner, would be most effective for this type of contamination and for the total removal of hydrocarbons. Brenntag carried out the pre-cleaning online to avoid having downtime and production losses.

"The big advantage of N-SPEC50E is that it can be processed by the refinery as a hydrocarbon and as far as experience tells us it does not disturb any of the downstream processes," explained Verkiel.

The second phase of the project involved the removal of the crude and all remaining wax, paraffin and heavy carbons inside the line, totalling a volume of 40000cubicmetres (Fig.2).

fter the line was taken out of service and depressurised, Brenntag established a pig train, comprising four designated pigs interspersed with a column of the required chemicals and water. Compressed air was applied as a propelling agent.

The advantage of compressed air is less waste disposal and time needed. Compared with nitrogen, it has the advantage of no issues with cold temperatures.

At the receiving site in Vlissingen, Brenntag created a steel dump line from the receiver to a temporary knockout vessel connected to containers. After all pigs were received, the line had to be depressurised again.

During depressurisation, the LEL of the out-flowing air was measured by an independent company Marsac at three sites: the launching site, the receiving site and the block valve station S3. According to Brenntag the results turned out to be outstanding: all sites measured zero per cent LEL.

After completing all required reconstruction and necessary maintenance actions, the line had to be filled up again with crude from the MOT in Rotterdam to Total’s refinery in Vlissingen. This was achieved by using two bidi separation pigs interspersed by a column of water, approximately 24cubicmetres. For this filling procedure, the knockout vessel with demister was used again; all out-coming air was blown into the environment without any spray while the LEL of this air remained at zeropercent.

Overall, the project showed that cleaning and emptying a large crude line using compressed air can be done in a safe and economical manner with N-SPEC cleaning chemicals.

The specific properties of N-SPEC chemicals enable the line to become totally hydrocarbon-free, which can result in a zeropercent LEL of the air inside the line.

The correct application of the product and the right safety precautions are crucial for a successful cleaning operation.

Total and Visser & Smit Hanab were both very pleased with the performance of Brenntag and the N-SPEC cleaning products. Based on this success, Brenntag has already been approached by other companies to carry out similar projects.

With over 10000 people working for it in over 50 countries and external sales last year of

FPAL is the oil and gas supply chain database for the UK and the Netherlands and is a division of management data company Achilles Information. It is the key tool used by purchasers in the oil and gas industry to identify and select current and potential suppliers when awarding supply contracts.

To qualify, all suppliers in the database have to go through an extensive process to create a complete company profile, including specific company data, information about products and services, HSE data, and project references.

FPAL currently matches the needs of over 70 purchasing organisations with the capabilities of over 2400 suppliers.

Benefits are achieved on both the purchaser and supplier side, through minimising and in many cases eliminating duplication work in the administrative processes related to sourcing of products and services.

Theo Verleun, business manager Brenntag O&G Europe, expects great exposure and growth in the North Sea area with this registration. "It’s a must-have for suppliers in the oil and gas offshore industry," he said. And the company has already been contacted by several purchasers through this database for tendering purposes. E6.1billion, Brenntag is one of the largest chemical distributors worldwide and provider of innovative pipeline cleaning solutions. In a new development, the company has been officially registered as a supplier in the first point assessment (FPAL) database.