SMT HAS ICE BUILDUP; UNABLE TO MAINTAIN ALT. REQUESTS HIGHER.

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I WAS BEING VECTORED FOR APCH TO 2G4 VIA GRV. WAS CLRED FROM 8000 FT TO 5000 FT MSL. AT 7000 FT STARTED PICKING UP LIGHT ICE. AT 5000 FT ICING WAS SEVERE -- 2 INCHES OF AIRFRAME ICE IN 4 MINS. ADVISED ATC I NEEDED HIGHER DUE TO ICE AND WAS ADVISED TO HOLD 5000 FT FOR A MIN. AFTER 1 MIN I CALLED CLBING OUT OF 5000 FT DUE TO ICE AND WAS THEN CLRED TO 8000 FT. COULD ONLY CLB TO 7600 FT. WAS VECTORED TO MORGANTOWN AND GIVEN LOWER AS ATC WAS ABLE; COULD NOT HOLD SOME ASSIGNED ALTS DUE TO ICE. IN THE AREA OF MORGANTOWN; WAS CLRED TO 2200 FT MSL. AT THIS ALT; ICE BEGAN MELTING. I DECLINED ILS APCH IN FAVOR OF FLYING A BOX PATTERN AT THIS ALT. THIS DECISION WAS MADE DUE TO 120 KT STALL SPD AND UNKNOWN LNDG CHARACTERISTICS WITH THIS AMOUNT OF ICE. AFTER 2 PATTERNS; ICE MELTED AND A 'NORMAL' ILS APCH WAS MADE. AT THE WORST POINT; AIR FRAME ICE WAS 2 INCHES AND LEADING EDGE ICE WAS 6 INCHES. BOOTS WOULD NOT BREAK IT OFF. BOOTS WERE CYCLED WHEN 5/8 - 3/4 INCH OF LEADING EDGE ICE HAD BUILT UP; BUT COULDN'T BREAK IT. IT WAS A COMBINATION OF CLR AND RIME ICE. PLT FEELS NO VIOLATIONS WERE COMMITTED AS ICE FORECASTS WERE FOR LIGHT TO MODERATE IN THIS AREA. PIREPS WERE MADE FOR SEVERE ICING. THE ATC FACILITY (CLARKSBURG APCH) DID A GREAT JOB OF COOPERATING. THIS COMBINED WITH PREVIOUS ICE RELATED EXPERIENCE OF PLT WERE AVOIDED. PLT FEELS CLR; CONCISE; AND FREQUENT COMS ON BOTH SIDES AVOIDED ANY MISHAP. TO SUM IT UP: COM AND COOPERATION AND CONSIDERATION PREVENTED A LOT OF AFTER-THE-FACT PAPERWORK.