Operating steel boilers

[maninshed]

Hi.
Wonder if someone can give me some help, I am thinking of building a 4" scale traction engine. The published design has a steel boiler, If I went ahead with the project I would buy a boiler from an established suplier no problem here. But what happens after that:-
a) I understand they have to be tested every two years, by an independant tester which is around £200, most clubs do not have people in place to test steel boilers. I understand ultrasonic testing is part of the test.
b) How long do steel boilers last?
c) What water treatments can be used to reduce corrosion.
d) Would joining the 'Model Road Vehicle Society' or some similar group be of benifit as far as testing goes.

regards Martyn

[alanstepney]

a) some clubs will test them. Worth checking those in your area.
b) a long time, with reasonable luck, 20+ years.
c) there is / was something called DM, which was excellent. An alternative is to talk to your local railway preservation society.
d) yes.

[spug103]

just thought id back up alans statements, and also mention, we have just had a 6" burrell te in the workshop for some replacement rivets on the bottom half of the firehole door, the only repair needed to the boiler after 22 years!!
it goes to show youve just got to look after them properly,
regards
ben

[gilesengineer]

Hi Martyn,

All of our locos have steel boilers (they're 10 1/4" Gauge), and it's not a problem.
We are part of the Southern Fed, and to date, our nominated club inspector gives them an annual inspection, followed by a cold water pressure (1 1/2 times) test followed by a steam test (all free......) Ultrasonic is NOT part of this - although I do have my own ultrasonic thickness tester.
A decent steel boiler, looked after, we would expect to get 40 years or so out of .... at least..... (would need re-tubing within that time in all likelihood)

Although we are railway orientated, several of our members have traction engines, and they get inspected and passed in the same way- and usually on the same day!

As Alan says, go to your local Preservation Society. The water's the same, the steel's the same, the chemical's the same (assuming you ARE local - the water DOES vary place-to-place, so the chemical you need varies.....) Magazines like Old Glory and Steam Railway also have good adverts for this kind of thing.

[taskerman]

Hi Martyn,
Might I suggest you use copper tubes, they are far more durable. I have them in my 6" tasker A1 with no problems. However they are not suitable for working pressures above 120 P.S.I.

[maninshed]

Taskerman, I did wonder about the option of copper tubes, thought they might be easier to change when the situation arrose, thanks for the advice.

Martyn.

[ewal]

Taskerman, who told you copper tubes wont stand more than 120lbs per sq inch?

ewal

[taskerman]

Ewal
Apparently it's all about the temperature of the steam at higher pressures and the modulus of elasticity.

[ewal]

I suppose it depends on the wall thickness. My boiler tubes have all been 3/4" diam x 1/16" wall & I have steamed them at 120 & pumped them to 600 with no problems. It certainly shows all the leaks.
ewal

[steam4ian]

G'day Ewal et al

The maximum allowable design tensile stress for copper (Sd) falls markedly with temperature.
Under 50 deg.C Sd = 41 MPa
Between 175-200 deg.C Sd = 21 MPa
Note saturated steam at 100 psi (700 kPa) has a temperature of about 170 deg.C
At 200 psi the strength of copper will be even less.

In Oz the Code for standard copper pipe does not appear to cover temperatures above 200 deg.C

Others may comment, but it would seem wise to me not to do a hydrotest on a hot boiler, certainly not over 50 deg.C.

Regards
ian

[kneedeepinswarf]

As my knowledge of boilers is rather limited, I hesitate to question the statement that copper tubes are unsuitable for pressures above 120 psi, but if so, how were the full-size railway companies able to run copper fireboxes at well beyond this pressure?

Lionel

[waggy]

Lionel,
Copper inner fireboxes are tied to the outer wrapper, backhead and throatplate by stays, which in effect make the inner and outer firebox one piece. The copper used in full size varies in thickness but averages around 5/8" thick, somewhat thicker than the tube wall. On our sizes we use plate that gives us somewhere in the region of an eight times safety factor, 3mm plate is common.
The tubes themselves aren't stayed to any other tube or plate, only supported at their ends.
Hope this answers your question.

Waggy.

[alanstepney]

Lots of stays...

[kneedeepinswarf]

Waggy and Alan,
Thank you for your very clear explanations. I can see that the inner firebox being stayed to the steel outer shell by so many stays would derive some strength from this arrangement. I suppose that copper tubes could be used for higher pressures but the wall thickness would become impractical, especially as the tubes also appear to act as stays for the upper part of the tube plate.

Lionel