Please help me settle an argument.

[lifechooser]

I have an MX-5 which has been turbocharged. The manifold is described as;

-1.50" Tubing for maximum flow
-Thick Gauge 1010 Heat Treated Mild Steel
-Fully machined flanges (1/2" machined, so somewhat thinner)
-Fully TIG welded

At it's recent MOT, it failed as the manifold had cracked. The garage took the manifold out and rewelded it. I've looked at their work and it looks good, however - on the MX5 forum someone has posted this;

Welding a turbo manifold is a specialist job.

You need to heat it up before welding etc.

A std garage whizzing over it with a Mig will last 2 minutes.

I can't see why it won't work, but to put my mind at rest I thought I would ask some experts.

What do you think? Is it ok, or should I get something else done to it? If so, what? I don't know what sort of welding was done, but as it's a local garage I'm assuming MIG.

Richard

 

[zardoz]

Well you would need to heat it before welding if it was alluminium or cast iron. however im not sure about heat treated steel. Maybe if its really thick stuff, but generally i'd say no. Im sure more experienced members will come along and point you straight, but unless you are sure which welding method was used it might all be academic.

 

[Arsonista]

If I remember, 1010 extrudes well, that's why it's used for tube work. It may also dissipate heat well too. Posh manifolds would be a problem if they are made from titanium or inconel, but 1010 is a commercial grade mild steel. I think. (Standby to be corrected).

 

[snowcat]

ermm its complected, I'm no expert on manifolds, however I have been around a bit, if its cracked its likely to continue cracking if its caused by a stress riser, or a fatigue crack this is to do with the cycling of the material, welding can make it more brittle if its not done properly( or in actual fact will always affect material propertys), pre heat can help as it helps to make a more ductile structure in the material it increases the grain size.......however its not always necessary

It depends on the position of the crack, the process used and the competence of the welder, which I hate to say at most garages is shocking.....

A couple of pictures may be of use.....

 

[lifechooser]

I can't easily take a photo right now. It sounds as though nothing is immediately coming to anyones mind. I'll keep an eye on it.

 

[Pete.]

It's likely to crack again, but you won't know if you don't try. Can't do a lot of harm anyway unless the turbo actually falls off. Just check it regularly.

 

[hotrodder]

Heat treated mild steel Suppose it could've been stress relieved after fabrication... maybe i've had too many cynical pills today but i smell marketing BS

If the garage just snotted over the crack then it'll be back (gross generalisation but MOT standard welding is designed to only last 10-11 months isn't it? ). The crack needs to be completely eliminated to stand a chance of long term survivial, with heavy wall pipe that means it'd need veeing out prior to welding. If the repair weld doesn't introduce a bunch of fresh stress risers (read: is reasonably smooth and tidy) then it may last a long time but as said thermal cycling and vibration can result in tiny flaws becoming cracks over time

 

[GeorgeKelley]

Plus, drill a small hole at either end of the crack before welding to kill the stress fracture, commonplace in cast iron applications to halt a crack