An alcohol flame lance to burn in roll up stove pipes

This post is about using an alcohol flame lance to change the shape memory of roll up stove pipes. It also considers techniques to help improve the shape of the stove pipe.

Note: This is just one little part of a 12 part series on improved stove pipe rolling. You may wish to start at Part 1 as hors d’oeuvres and then taste from the banquet.

Introduction

I have made several roll up flue pipes out of titanium and stainless steel foil. Despite the thinness of the foils they strongly resist the formation of the desired tubular flue pipe shape. The good initial formation of the pipe shape is critical to prevent the formation of ‘crinkles’ (example A. below). These crinkles will be ‘remembered by the metal and spoil the sealing qualities of the pipe joint for the rest of its life.

In the videos below the best job is done carefully at home with help from a coordinated team of people with gloved hands. “Not in the bush by your self with cold hands, on a lumpy snow surface and the snow falling on you.”

A. Solo forming, causing many sharp crinkles that will diminish the quality of the pipe over its long life. How not to roll a flue pipe for the first time

B. Two people rolling the stove pipe, causing fewer crinkles. Better flue pipe rolling for the first time

C. A well-organized team of three people rolling the pipe and causing only a few minor crinkles. Excellent flue pipe rolling

The forming of the stove pipe by the last team is good. However, there are better crinkle-free methods that are the subject of other posts in this series.

Using heat to form a new memory of the flue pipe shape

All this good work at home will be wasted (or at best be simple practice run) if the formed pipe is not heat conditioned in this new shape so that it will be remembered, for its whole life, when you deploy it in the bush. The above videos indicate that using the pipe on the stove will provide this heat memory.

The problem with this approach is that it works well for the bottom end of the pipe that is closest to the stove, but not for the rest. This can be improved a little by additionally running the pipe ‘up-side-down’, but the midsection is still not good, particularly for long pipes.

Heat treating stove pipes inside another insulated pipe

In an attempt to address this issue, I made a set of insulated tubes of stainless steel foil that slipped over the formed flue pipe. These were covered with zirconia felt insulation that was covered with aluminium foil. These tubes were put over the stove pipe for heat treatment, on the stove, using them as a substitute for the normal retaining rings.

The idea was that the heat would be trapped within the pipe and the required temperature for establishing the new memory would move high up, possibly to the midsection of the pipe.

This technique worked to some extent, but the middle of the pipe was underdone. I think this was because of the ‘curse’ of lamina flow that establishes is such pipes and it prevents good heat exchange to the wall of the pipe, through lack of turbulence.

This issue is discussed in my tent stove articles. The temperature of the hot core of gas in the centre of the pipe can be 200 C greater than the metal temperature on the outside. The hotter the flue gas gets the greater this temperature differential gets.

Interestingly, I used similar experimental insulators made mainly out of aluminium foil and zirconia felt. In the turbulent zone (for approximately 300mm up from the stovetop) the titanium pipe got so hot that the aluminium foil melted and permanently bonded to the titanium flue pipe (est 660 C). I am reminded of this every time I use this pipe. Even so, the upper reaches of the pipe did not have an adequately modified shape memory.

To address this residual problem I have for some time contemplated using a gas flame lance (garden weed burner) to quickly produce a full memory effect along the entire flue pipe.  However, the lance stem was not long enough and lamina flow was still my enemy.

The making of a new stainless steel flue pipe for a stove gave me the opportunity to test out some new ideas. I had been tinkering with alcohol stoves with heat risers and watched with delight as the rather pathetic alcohol flame produced a red hot rim (500+C) on the top of the heat riser.

Next, seeing a discarded Berocca tube gave me the idea of making a simple alcohol flame lance. “By the way, I don’t use Berocca, I think they are a waste of time and money if you have a balanced diet, but the tubes and lids are a great tinkering resource.”

Sorry for such a long introduction, but the task of taming a beautiful but feisty rolled strip of metal foil into a compliant self-forming quality flue pipe is not simple. It is made more complex dealing with sharp edges while dancing with flames. This is especially so if you want a quality pipe for the long term without nasty crinkles. You will be relieved to know that the solution to the problem is short and sweet.

Flue pipe burning in with an alcohol flame lance

I put a long wick, made from a rolled-up piece of paper towel, into a Berocca tube of alcohol to form a lance. I drove a banboo pole into the ground and then mounted lance on top of it. After lighting the ~40mm protruding wick I put the end of a newly formed flue pipe over the flame and lowered the tube down over the flame. The characteristic roar of a strong turbulent flame and the heat radiating from the pipe through my thick leather gloves told me that I had success within reach.

This allowed me to safely insert the flame lance into the flue pipe (or more correctly put the pipe over the lance) without blocking the airflow up around the tube.

I think the turbulence of the air squeezing around the Berocca tube was creating a venturi vacuum and turbulence around the wick. This action improved the combustion by better mixing of the air with the alcohol. The turbulence also improves the heat exchange to the adjacent flue pipe wall.

For the first time, I was able to rapidly and safely memory treat any part of a long flue pipe.

Initially, I started to condition the lower end of the pipe and moved my way up to the centre. While this was thermally more efficient. I quickly realised that it was much more practical (and safe) to start in the middle and slowly withdraw the lance (or lift the pipe). This means that the pipe can be grasped by the cool bottom section and then be grasped by the other gloved hand as the lowest part is finally heat treated.

Heat treating of a stove pipe video

Discussion

The alcohol flame lance provides a cheap, quick, gentle and even method of developing a new memory in a virgin rollup stove pipe. It also means that the careful work of forming the desired shape will be preserved indefinitely in the foil for the long term and reduces the risk of crinkle damage.”Just remember that any crinkles will also be preserved!”

When I ‘burn-in’ a virgin flue pipe, by this or any other method, I use many more retaining rings as this creates a more circular shape and more even join line.

All my tent stoves, as far as I know, are very different from others. They are designed to burn very efficiently and cleanly using miserly amounts of damp sticks (~400g/hour). This means that they put most of the heat of combustion into radiant heat for the occupants of the tent (not much to spare for heating the flue pipe).

There are no boastful flames shooting out of my flue pipes as the combustion is largely done inside the high-temperature burner and completed in the front end of the cooktop/heat exchanger labyrinth. Other stoves that are much more powerful may be able to adequately heat a lot more of the flue pipe to the temperature required for setting a new shape memory.

I tried to find a photo of such a boastful flame and could only find my own, so it will suffice to make my point. Where there is such a flame, the temperature inside the flue pipe might be adequate to impart the new shape-memory to a whole flue pipe. However, bear in mind that the flame shown in the photo above is from a burner with no heat exchanger and is on top of a pipe that is only about 500mm long. It also required a rather unusual saturation burn with hydrocarbons to achieve this effect. 

The downside of this new memory

The downside of this new strong memory of an even tighter curvature is that it makes the metal more feisty and difficult to roll up for backpacking. Luckily, my telescopic stove pipe screwing and open sloppy spiral deployment methods solve this problem. The rolled up pipe becomes a safe, easy and compact roll without crinkle damage with the holding rings in place.

Tim

Addendum

Since preparing this post I have made a better and stronger gas-flame lance and an even stronger charcoal-fired lance.