What are folks using as a porous plug material for your flexible stays per CFR 230.41 part b?

230.41 Flexible staybolts with caps.

(a) General. Flexible staybolts with caps shall have their caps removed during every 5th annual inspection for the purpose of inspecting the bolts for breakage, except as provided in paragraph (b) of this section.

(b) Drilled flexible staybolts. For flexible staybolts that have telltale holes between 3⁄16 inch and 7⁄32 inch in diameter, and which extend the entire length of the bolt and into the head not less than one third of the diameter of the head, the steam locomotive owner and/or operator need not remove the staybolt caps if it can be established, by an electrical or other suitable method, that the telltale holes are open their entire length. Any leakage from these telltale holes during the hydrostatic test indicates that the bolt is broken and must be replaced. Before the steam locomotive is placed in service, the inner ends of all telltale holes shall be closed with a fireproof porous material that will keep the telltale holes free of foreign matter and permit steam or water to exit the telltale hole when the bolt is broken or fractured.

Mike,
Yes 230.41b states "porous material". Don't use brick mortar, sairset. This is made to vitrify (turn to a glassy state). Sairset also has binders, sodium, silica and sodium silicate which makes it bind to metal and brick. This is not by definition a porous plug.

Flannery made plugs which was just a cone shaped chalk plug which was pushed into the hole and then the proud end snapped off. Chalk is basically calcium carbonate with some clay as a binder. Calcium does not go into a melt at the firebox temperature that we see.

Manufacturing chalk plugs probably is not cost effective so then the next best thing is a product that is like chalk. Drywall joint compound is made with limestone which is a different form of calcium and some organic binders. Just load the joint compound into a caulk gun, the type that is made to be loaded with your material, and then squeeze a small amount into the telltale hole. The firebox should be clean of soot first as the soot makes the application a little harder. We have been using joint compound for some years now. The compound does not vitrify and is easily hydrated. That is if water hits it then it turns back to mud and washes away. removing the plugs is very easy and just powders away with a 3/16 masonry bit. We use ready mixed compound and do not add water.

We did a test using sairset (brick mortar) and joint compound. In our test fixture we had holes plugged with sairset, fired to firebox temperature and then also had a like fixture with joint compound fired to the same temperature. We did push tests to remove the plugs and found that the mortar did not come loose until it was many times over MWP. The joint compound came loose at a pressure lower than MWP. We used 230PSI as our standard. I have been told that a broken bolt will have a shock effect as water enters the telltale. Then how about a cracked bolt that lets water enter at a reduced rate? Someone will have to show me that one. We are sticking with joint compound. For all the reasons, it works and satisfies 230.41